Effects of COVID-19 lockdown on heart rate variability

Nicolas Bourdillon; Sasan Yazdani; Laurent Schmitt; Grégoire P Millet

doi:10.1371/journal.pone.0242303

. 2020 Nov 12;15(11):e0242303. doi: 10.1371/journal.pone.0242303

Effects of COVID-19 lockdown on heart rate variability

Nicolas Bourdillon ^1,^2,^*, Sasan Yazdani ², Laurent Schmitt ³, Grégoire P Millet ¹

Editor: Daniel Boullosa⁴

PMCID: PMC7660489 PMID: 33180839

Abstract

Introduction

Strict lockdown rules were imposed to the French population from 17 March to 11 May 2020, which may result in limited possibilities of physical activity, modified psychological and health states. This report is focused on HRV parameters kinetics before, during and after this lockdown period.

Methods

95 participants were included in this study (27 women, 68 men, 37 ± 11 years, 176 ± 8 cm, 71 ± 12 kg), who underwent regular orthostatic tests (a 5-minute supine followed by a 5-minute standing recording of heart rate (HR)) on a regular basis before (BSL), during (CFN) and after (RCV) the lockdown. HR, power in low- and high-frequency bands (LF, HF, respectively) and root mean square of the successive differences (RMSSD) were computed for each orthostatic test, and for each position. Subjective well-being was assessed on a 0–10 visual analogic scale (VAS). The participants were split in two groups, those who reported an improved well-being (WB+, increase >2 in VAS score) and those who did not (WB-) during CFN.

Results

Out of the 95 participants, 19 were classified WB+ and 76 WB-. There was an increase in HR and a decrease in RMSSD when measured supine in CFN and RCV, compared to BSL in WB-, whilst opposite results were found in WB+ (i.e. decrease in HR and increase in RMSSD in CFN and RCV; increase in LF and HF in RCV). When pooling data of the three phases, there were significant correlations between VAS and HR, RMSSD, HF, respectively, in the supine position; the higher the VAS score (i.e., subjective well-being), the higher the RMSSD and HF and the lower the HR. In standing position, HRV parameters were not modified during CFN but RMSSD was correlated to VAS.

Conclusion

Our results suggest that the strict COVID-19 lockdown likely had opposite effects on French population as 20% of participants improved parasympathetic activation (RMSSD, HF) and rated positively this period, whilst 80% showed altered responses and deteriorated well-being. The changes in HRV parameters during and after the lockdown period were in line with subjective well-being responses. The observed recordings may reflect a large variety of responses (anxiety, anticipatory stress, change on physical activity…) beyond the scope of the present study. However, these results confirmed the usefulness of HRV as a non-invasive means for monitoring well-being and health in this population.

Introduction

The COVID-19 pandemic in 2020 resulted in strict confinement rules in France for 8 weeks, from 17 March to 11 May, period known as the lockdown. Its aim was to slow down the spread rate of COVID-19, therefore saving lives and decreasing the workload in hospitals, which capacity to treat new patients was exceeded. Restrictions during the lockdown included closed gyms and sports centers, plus limitations on the duration spent outdoors, maximum walking distance from home which, associated with the lack of space and appropriate devices in homes for physical exercise, and lack of technical knowledge of the population on appropriate training routines, may have resulted in decreased physical activity. A survey by the French public health national institute “Santé Publique France” [1] published on 17^th June 2020 confirmed that 47.4% of the population declared a decrease in physical activity, especially (58.9%) in walking time, during the lockdown period. Contradictory, a minority (17.9%) used this period for increasing their physical activity. In addition, 33.4% of the population declared spending more than 7h seated. The average daily seated time was 6h19. Beyond these self-declared data, the impact of the lockdown period remains unclear, strong psychological impacts have been reported in a review [2] and specifically to the COVID-19-related lockdown [3], as well as metabolic and body composition outcomes [4], but one may hypothesize that it may have led to changes in cardiovascular fitness and psychological states.

Exercise plays a fundamental role in cardiovascular health [5] but also in mitigating some of the possible psychological impacts of lockdown [6]. In those cases, aerobic exercises such as walking or endurance running appears to be more beneficial than sprint running or force/power exercises [6, 7]. Heart rate variability (HRV) is a commonly used method for cardiovascular follow-up in athletes [8], healthy people [9] cardiovascular patients [10], and is related to self-regulations at the cognitive, emotional, social and health levels [11, 12]. Specifically, HRV analysis allows to evaluate the modulation of the sympathetic and parasympathetic branches of the autonomic nervous system. The low-frequency (LF) band reflects a mix of sympathetic and parasympathetic modulations on the heart [13] and has been proposed as an index of the sympathovagal balance [14]. The migration of the respiratory sinus arrhythmia in the low-frequency band is a subject of debate [15], and it is not the only issue regarding the physiological meaning of LF [16], which leaves the physiological implications of this frequency band unclear [17]. Respiratory sinus arrhythmia is the main phenomenon provoking changes in the HF band and RMSSD which therefore mainly reflects parasympathetic influences on the heart [18, 19]. Physical exercise increases the parasympathetic tone [20]. Hypotonia is a sign of cardiovascular deconditioning [21]. Finally, HRV-based methods may be used to assess autonomic imbalances, diseases [10], stress and well-being [12].

To the best of our knowledge, HRV parameters before, during and after the lockdown period have not been reported in the literature. Therefore, the aim of the present study was to report HRV parameters to demonstrate the effects of lockdown and to investigate whether changes in HRV were related to some changes in psychological states during and after this period. We hypothesized that alteration in parasympathetic-related markers (i.e., decreases in RMSSD and HF, increase resting HR) would reflect a negative feeling over the period, whilst a minority of the population would report an improved subjective feeling with consequences on HRV, potentially in line with the report by Santé Publique France [1].

Methods

Experimental design

Strict lockdown (further denoted CFN) rules were applied in France over 8 weeks, from 17 March to 11 May 2020. The lockdown was unexpected, therefore there was no previous intention to study its effects on HRV. Nevertheless, data collection was performed for the purpose of this study, using recording devices distributed to the participants before the lockdown. The equipment consisted of a RR-interval-measuring chest strap and a dedicated mobile application that recorded both RR intervals from the strap and a declared visual analogic scale (VAS). When accepting to use the mobile app, the participants accepted the participation in the study. Three periods were compared: From 1 January to 16 March (baseline, BSL); from 17 March to 11 May (CFN), and from 12 to 31 May (recovery, RCV). The local ethical committee approved the study (agreement 2016–00308; Commission Cantonale d’Ethique de la Recherche sur l’être humain, CCER-VD; Lausanne, Switzerland) as part of a set of studies on a broader scale. All experimental procedures conformed to the standards set by the Declaration of Helsinki.

Participants

Inclusion criteria were, age between 18 and 60 years old. All subjects self-declared being physically active, healthy, non-smokers, with no known diseases and no pregnancy or lactation for women as well as living in France. The initially planned study involved physical exercises with a maximum age for inclusion criteria of 60 years-old to limit the cardiovascular risks. Out of the database (n = 112), participants with at least forty orthostatic tests between 1 January and 31 May 2020 and at least 10 tests in each period of three periods (BSL, CFN and RCV) were extracted (n = 95). More specifically, from January 1^st to May 11^th (end of lockdown) there were 20 weeks. With 2 tests per week in average per participant, 40 tests were performed.

Heart rate variability

The participants performed an orthostatic test (5 minutes supine followed by 5 minutes in the standing position) on a regular basis between the 1^st of January 2020 and the 31^st of May 2020 [22]. This orthostatic test had to be performed, in the morning, upon wake-up, with an empty bladder, and before breakfast. The inter-beat interval (RR interval) measuring device (sensor H7 + chest belt, Polar, Kempele, Finland or cardiosport TP5+, Cardiosport, Waterlooville, UK) was connected to the participants’ smartphones via Bluetooth (mobile application: inCORPUS^® v2.1.3, be.care SA, Renens, Switzerland). The H7 is the most used RR-recording device, the TP5+ uses the exact same technology [23]. The smartphone application is a Bluetooth receiver, using the standard BLE protocol, which does not interfere in any ways with the recording.

The participants were walked through the test by the dedicated mobile application, they started the recording from the application, in the supine position. After five minutes the smartphone beeped, at which point the participants immediately stood and pressed a button on the application to start the recording of the standing phase. After five minutes in the standing phase the smartphone beeped again to inform that the test was over. At that point, the participants were asked to fill-up the VAS by sliding the cursor according to their sensation of the moment. The transition phase between the supine and the standing positions last 3 to 8 s on average. The HRV analysis does not take into account the first minute of recording in each position. Data were immediately and automatically transferred to our servers for analysis. Therefore, meetings between participants and researchers were avoided, in the respect of the strict lockdown rules applying. Becare S.A. employees controlled that the participants properly used the mobile application and chest belt and responded quickly to any question from the participants using dedicated chat bots, emails or telephone.

Out of each of the 5-minute periods, the first minute was used as a stabilization period and was excluded from the analysis whilst the last four minutes were analyzed for HRV.

The RR intervals from the orthostatic tests were first analyzed to remove ectopic beats from the recordings, the algorithms used are currently not available to the public. Ectopic beats were then compensated for by means of interpolation to calculate normal-to-normal (NN) intervals. From the NN intervals, the following heart rate variability (HRV) parameters were extracted: mean HR; the root mean square of the successive differences (RMSSD); the spectral power in the low-frequency (LF, 0.04–0.15 Hz) and high-frequency bands (HF, 0.15–0.40 Hz) in ms²; and the values (expressed in normalized units) for LF and HF, labelled nLF and nHF, respectively [8, 24]. The spectral power was estimated using a fast Fourier transform on the resampled NN intervals (4 Hz) using a window length of 250 data points and an overlap of 50%. All computations were performed separately for the supine (SU) and standing (ST) positions using. All analyses were performed using MATLAB^® (R2019a, MathWorks, Natick, MA, USA).

Visual analogic scale (VAS)

On the mobile application, for each test, the participants were required to rate their well-being “how do you feel today?” using a visual analogic scale (VAS) graduated from 0 to 10.

Statistics

All results are given as mean ± SD. For display purposes SEM is plotted on all figures. HR and HRV units were normalized with respect to BSL. The Kolmogorov-Smirnov test was used to ensure normality of the data. Measurements were evaluated with a two-way ANOVA analysis for time effect (BSL, CFN and RCV) and group effect (WB- vs. WB+). Regarding the group effect division adopted (WB- vs WB+), the criteria was a change in VAS >2, that corresponded to 20% change in the scale. Such a large change aimed to lower the intra-individual variability. The statistical power of the performed tests was set at p = 0.05 for significance and p = 0.10 for tendency. The Tukey-Kramer post-hoc was used when appropriate. Statistical power SP is reported for each ANOVA performed, the computations take into account the F-statistic values (expected and observed) and the degrees of freedom [25, 26]. ANOVA analyses were carried out on unitary values (i.e. no average per period or otherwise). Correlations were computed for LF, HF, HR and RMSSD against VAS, in the supine and the standing positions, regardless of the time points (BSL, CFN and RCV), which means that all data points were pooled when computing the correlations. Correlations were made using MATLAB^® (R2019a, MathWorks, Natick, MA, USA). Statistical analyses were performed using MATLAB^®.

Results

Ninety-five participants (27 women, 68 men) were included in this report (age 37 ± 11 years, height 176 ± 8 cm, weight 71 ± 12 kg). Out of these participants, 20% (WB+, n = 19; 5 women, 14 men; age 36 ± 13 years, height 178 ± 10 cm, weight 74 ± 13 kg) showed an improved well-being, estimated by the positive change (>2) in the 0–10 VAS score between BSL and CFN. Contradictory, most of the participants (WB-, n = 76; 22 women, 54 men; age 38 ± 11 years, height 175 ± 7 cm, weight 69 ± 12 kg) did not improve or deteriorated this VAS score during the CFN period.

Fig 1 shows the negative impact of CFN in the WB- group, with a general alteration in parasympathetic activity in the supine position, as shown by the increased supine HR and decreased RMSSD in CFN and RCV compared to BSL (SP = 0.76). There was a tendency for a decrease in RMSSD between CFN and RCV (SP = 0.99). There was also a decrease in HF in RCV compared with BSL (SP = 0.48). In the standing position, there was a significant increase in HR in CFN compared to BSL (SP = 0.64), but there was no change on the other parameters. All these changes are reported in normalized units.

Fig 2 shows the positive impact of CFN in the WB+ group with a decrease in supine HR in CFN and RCV compared to BSL (SP = 0.85), an increase in supine RMSSD in CFN and RCV compared to BSL and an increase in RCV compared to CFN (SP = 0.99). There was also an increase in LF (SP = 0.36) and HF (SP = 0.98 and therefore total power) in RCV compared to BSL, and an increase in HF in RCV compared to CFN. There was no change in the standing position. All these changes are reported in normalized units.

There was an interaction time x group for HR, RMSSD and HF (p < 0.001, SP = 0.69; p < 0.001, SP = 0.90; and p <0.01, SP = 0.65; respectively) in the supine position. There was a significant interaction for HR only (p<0.05, SP = 0.42) in the standing position. In the supine position, HR was significantly higher in the WB- group compared to the WB+ group in CFN and RCV. RMSSD was significantly lower in the WB- group compared to the WB+ group in CFN and RCV. HF was significantly lower in the WB- group compared to the WB+ group in RCV. In the standing position HR was significantly higher in the WB- group compared to the WB+ group in CFN.

There were significant correlations (p < 0.001 for all) between VAS and HR ((R = -0.24), RMSSD (R = 0.14) and HF (R = 0.19) on the whole population in the supine position. The higher the VAS score (i.e., subjective well-being), the higher the RMSSD and HF and the lower the HR. Moreover, RMSSD in standing position was correlated to VAS. All Pearson’s correlation data are listed in Table 1. All correlations were computed on absolute values.

Table 1. Pearson’s correlation coefficient (R), p value, and 95% confidence interval (CI) in the supine and standing positions for HR and HRV parameters against VAS.

	R	p	CI
	supine
LF (ms²)	0.07	0.08	-0.01 0.15
HF (ms²)	0.14	< 0.001	0.06 0.22
HR (bpm)	-0.24	< 0.001	-0.3–0.18
RMSSD (ms)	0.19	< 0.001	0.11 0.27
	standing
LF (ms²)	-0.01	0.89	-0.12 0.10
HF (ms²)	0.08	0.15	-0.03 0.19
HR (bpm)	-0.02	0.52	-0.09 0.04
RMSSD (ms)	0.10	0.01	0.03 0.17

Open in a new tab

When dividing the CFN period in two sub-periods of 4 weeks, there were no differences in any of the parameter between CFN1 and CFN2, suggesting a relative stability across CFN (S1 Data).

Discussion

The present study aimed to investigate the HRV responses of participants exposed to the strict lockdown that occurred in France. We found that HRV changes from BSL to CFN and RCV were contradictory between two groups who did vs. did not deteriorate their subjective well-being over these periods. In 80% of the participants, parasympathetic-related HRV parameters (i.e., RMSSD, HF) measured in the supine position were decreased concomitantly to a psychological alteration. Contradictory, in 20% of the participants, both supine HRV and well-being were improved. Standing HRV was not modified during CFN.

The sudden lockdown that occurred implied drastic changes in the lifestyle of the participants, which is generally a stressor factor. Moreover, the psychological impact of lockdown included negative psychological effects, such as frustration, boredom, loss of social contacts, [2] inadequate supplies, inadequate information, financial loss, infection fears, confusion, and anger [27, 28]. The participants in the present study lived in France, where a survey of the French national public health institute (Santé Publique France) demonstrated a drastic decrease in physical activity and increased time spent in the seated position [1]. In the present study, physical activity was not measured, but only subjective feeling of well-being, measured by a VAS with a smartphone. This resulted in 20% of the participants who rated positively the lockdown period, since VAS score improved by at least 2 on the 0–10 scale. Interestingly, this is in line with data from the French national public health institute, who reported that 18% of the French population declared an increase in physical activity. Obviously, well-being can be determined by many causes and physical activity is only one of them. In this increasing well-being, the fact that increased RMSSD, LF and HF (associated to decreased HR) were also observed post lockdown, may be a marker of an effective and lasting improvement in cardiovascular health. The best responses occur when both the sympathetic and parasympathetic influences on the heart are high [29, 30] hence increased LF and HF, associated to decreased resting HR.

Beyond this speculative influence of physical activity, there are many stressors during lockdown [2]: subjective (i.e., poor information on the duration of the lockdown, the fears of infection, frustration and boredom, sense of isolation, anger, guilt, helplessness, loneliness, nervousness, sadness) or objective (i.e., inadequate supplies, financial concerns, altered usual day-to-day activities etc.) sources of stress have an impact on psychological outcomes and indirectly on HRV.

There were significant correlations between VAS and HRV, which was positive for HF and RMSSD and negative for HR. Therefore, the better the participants felt, the higher the parasympathetic influences and the lower the HR, and vice-versa the lower the HF and RMSSD, the lower the feeling of well-being. Most of these correlations were found when HRV was measured in supine position, except for RMSSD in standing position. This later result emphasizes the value of RMSSD as a key parameter of HRV analysis. Moreover, these results emphasize the usefulness of HRV as a global index of heath in the general population. In line with previous literature and data from the national French public health institute, the more active people during the lockdown may have felt better [1, 2].

Limitations

The lockdown was applied suddenly, and it was therefore impossible to recruit participants a priori during the baseline period. By chance we had enough participants with sufficient HRV tests to conduct this study. Overall, it is a unique opportunity to describe the HRV behavior in 95 healthy people, extracted from a database of 7098 orthostatic tests. The main limitation is that we did not have any data on physical activity of these participants. We can only speculate that the HRV changes during CFN reflect at least partly the decrease or increase in physical activity. Another important limitation of the present study is that our sample did not allow any other group divisions, evidently justifiable by literature, as by age clusters or gender that may be predictors of negative psychological impacts of lockdown. Moreover, Hnatkova et al. [31] showed that heart rate responses to postural changes may be different for sex. Finally, the VAS allowed to only rate a “general well-being” but not any specific mood components as vigor, anxiety, anger etc. Therefore, it remains vague and incorporates probably different psychological states among participants.

Through questionnaire in the application and for each test, the participants declared their potential lack of sleep, alcohol consumption (as limited as possible), digestive problems and other potential confounding factors that may have modified the HRV parameters reported in this study. Those factors are known as key in HRV and well-being alterations and may partly explain the cardiovascular deconditioning observed. However, in the present study, we did not find any factor that may have explained the differences between the two groups.

The separation criterion between the WB+ and WB- groups was arbitrary

Conclusion

The lockdown in France was sudden and severe, inducing an increase in many subjective and objective stressors as well as drastically limiting the possibilities for physical activities. This likely resulted in a stressful situation that may lead to negative psychological outcomes and/or cardiovascular health (i.e., decreased RMSSD and HF and increased resting heart rate in supine position) in most of the population. However, in 20% of the participants the lockdown was positively rated, as shown by an improved well-being and parasympathetic activity. Altogether, the present study confirms the usefulness of regular HRV testing in this population for monitoring health status, as previously shown in elite athletes.

Supporting information

S1 Data

(TXT)

Click here for additional data file.^{(65B, txt)}

Data Availability

Data underlying the study is available on Zenodo (http://doi.org/10.5281/zenodo.4058116).

Funding Statement

NB and SY are employees of becare SA. GPM and LS have no conflict of interests. becare SA did not play a role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript and only provided financial support in the form of NB and SY salaries. The funder provided support in the form of salaries for authors NB and SY, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.

References

1.Lemoine V, Delibéros M, Bessarion C, Champion S. Confinement: un impact certain sur l’activité physique, le temps passé assis et le temps passé devant un écran. Press Release. 2020. https://www.santepubliquefrance.fr/presse/2020/confinement-un-impact-certain-sur-l-activite-physique-le-temps-passe-assis-et-le-temps-passe-devant-un-ecran [Google Scholar]
2.Brooks SK, Webster RK, Smith LE, Woodland L, Wessely S, Greenberg N, et al. The psychological impact of quarantine and how to reduce it: rapid review of the evidence. Lancet Lond Engl. 2020;395: 912–920. 10.1016/S0140-6736(20)30460-8 [DOI] [PMC free article] [PubMed] [Google Scholar]
3.Wang C, Pan R, Wan X, Tan Y, Xu L, Ho CS, et al. Immediate Psychological Responses and Associated Factors during the Initial Stage of the 2019 Coronavirus Disease (COVID-19) Epidemic among the General Population in China. Int J Environ Res Public Health. 2020;17 10.3390/ijerph17051729 [DOI] [PMC free article] [PubMed] [Google Scholar]
4.Martinez-Ferran M, de la Guía-Galipienso F, Sanchis-Gomar F, Pareja-Galeano H. Metabolic Impacts of Confinement during the COVID-19 Pandemic Due to Modified Diet and Physical Activity Habits. Nutrients. 2020;12 10.3390/nu12061549 [DOI] [PMC free article] [PubMed] [Google Scholar]
5.Lavie CJ, Arena R, Swift DL, Johannsen NM, Sui X, Lee D-C, et al. Exercise and the cardiovascular system: clinical science and cardiovascular outcomes. Circ Res. 2015;117: 207–219. 10.1161/CIRCRESAHA.117.305205 [DOI] [PMC free article] [PubMed] [Google Scholar]
6.Pareja-Galeano H, Sanchis-Gomar F, Lucia A. Physical activity and depression: type of exercise matters. JAMA Pediatr. 2015;169: 288–289. 10.1001/jamapediatrics.2014.3501 [DOI] [PubMed] [Google Scholar]
7.Brown HE, Pearson N, Braithwaite RE, Brown WJ, Biddle SJH. Physical activity interventions and depression in children and adolescents: a systematic review and meta-analysis. Sports Med Auckl NZ. 2013;43: 195–206. 10.1007/s40279-012-0015-8 [DOI] [PubMed] [Google Scholar]
8.Schmitt L, Regnard J, Parmentier AL, Mauny F, Mourot L, Coulmy N, et al. Typology of “Fatigue” by Heart Rate Variability Analysis in Elite Nordic-skiers. Int J Sports Med. 2015;36: 999–1007. 10.1055/s-0035-1548885 [DOI] [PubMed] [Google Scholar]
9.Hynynen E, Konttinen N, Kinnunen U, Kyröläinen H, Rusko H. The incidence of stress symptoms and heart rate variability during sleep and orthostatic test. Eur J Appl Physiol. 2011;111: 733–741. 10.1007/s00421-010-1698-x [DOI] [PubMed] [Google Scholar]
10.Thayer JF, Yamamoto SS, Brosschot JF. The relationship of autonomic imbalance, heart rate variability and cardiovascular disease risk factors. Int J Cardiol. 2010;141: 122–131. 10.1016/j.ijcard.2009.09.543 [DOI] [PubMed] [Google Scholar]
11.Laborde S, Mosley E, Thayer JF. Heart Rate Variability and Cardiac Vagal Tone in Psychophysiological Research—Recommendations for Experiment Planning, Data Analysis, and Data Reporting. Front Psychol. 2017;8: 213 10.3389/fpsyg.2017.00213 [DOI] [PMC free article] [PubMed] [Google Scholar]
12.Kim H-G, Cheon E-J, Bai D-S, Lee YH, Koo B-H. Stress and Heart Rate Variability: A Meta-Analysis and Review of the Literature. Psychiatry Investig. 2018;15: 235–245. 10.30773/pi.2017.08.17 [DOI] [PMC free article] [PubMed] [Google Scholar]
13.Holzman JB, Bridgett DJ. Heart Rate Variability Indices as Bio-Markers of Top-Down Self-Regulatory Mechanisms: A Meta-Analytic Review. Neurosci Biobehav Rev. 2017. 10.1016/j.neubiorev.2016.12.032 [DOI] [PubMed] [Google Scholar]
14.Goldberger JJ. Sympathovagal balance: how should we measure it? Am J Physiol. 1999;276: H1273–1280. 10.1152/ajpheart.1999.276.4.H1273 [DOI] [PubMed] [Google Scholar]
15.Wang Y-P, Kuo TBJ, Li J-Y, Lai C-T, Yang CCH. The relationships between heart rate deceleration capacity and spectral indices of heart rate variability during different breathing frequencies. Eur J Appl Physiol. 2016;116: 1281–1287. 10.1007/s00421-016-3332-z [DOI] [PubMed] [Google Scholar]
16.Medeiros AR, Michael S, Boullosa DA. Make it easier! Evaluation of the “vagal-sympathetic effect” in different conditions with R-R intervals monitoring. Eur J Appl Physiol. 2018;118: 1287–1288. 10.1007/s00421-018-3855-6 [DOI] [PubMed] [Google Scholar]
17.Hayano J, Yuda E. Pitfalls of assessment of autonomic function by heart rate variability. J Physiol Anthropol. 2019;38: 3 10.1186/s40101-019-0193-2 [DOI] [PMC free article] [PubMed] [Google Scholar]
18.Pomeranz B, Macaulay RJ, Caudill MA, Kutz I, Adam D, Gordon D, et al. Assessment of autonomic function in humans by heart rate spectral analysis. Am J Physiol. 1985;248: H151–153. 10.1152/ajpheart.1985.248.1.H151 [DOI] [PubMed] [Google Scholar]
19.Force Task. Heart rate variability. Standards of measurement, physiological interpretation, and clinical use. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Eur Heart J. 1996;17: 354–381. [PubMed] [Google Scholar]
20.Dixon EM, Kamath MV, McCartney N, Fallen EL. Neural regulation of heart rate variability in endurance athletes and sedentary controls. Cardiovasc Res. 1992;26: 713–719. 10.1093/cvr/26.7.713 [DOI] [PubMed] [Google Scholar]
21.Buchheit M. Monitoring training status with HR measures: do all roads lead to Rome? Front Physiol. 2014;5: 73 10.3389/fphys.2014.00073 [DOI] [PMC free article] [PubMed] [Google Scholar]
22.Bourdillon N, Schmitt L, Yazdani S, Vesin J, Millet GP. Minimal Window Duration for Accurate HRV Recording in Athletes. Front Neurosci. 2017;11: 456 10.3389/fnins.2017.00456 [DOI] [PMC free article] [PubMed] [Google Scholar]
23.Plews DJ, Scott B, Altini M, Wood M, Kilding AE, Laursen PB. Comparison of Heart-Rate-Variability Recording With Smartphone Photoplethysmography, Polar H7 Chest Strap, and Electrocardiography. Int J Sports Physiol Perform. 2017;12: 1324–1328. 10.1123/ijspp.2016-0668 [DOI] [PubMed] [Google Scholar]
24.Thorpe RT, Strudwick AJ, Buchheit M, Atkinson G, Drust B, Gregson W. Tracking Morning Fatigue Status Across In-Season Training Weeks in Elite Soccer Players. Int J Sports Physiol Perform. 2016;11: 947–952. 10.1123/ijspp.2015-0490 [DOI] [PubMed] [Google Scholar]
25.Zar JH. Biostatistical Analysis (2nd ed.). Prentice-Hall,. Prentice-Hall,. NJ: Englewood Cliffs; 1999. pp. 195–196. [Google Scholar]
26.Scheffé H. The Analysis of Variance. The Analysis of Variance. New-York: John-Wiley; 1959. p. 227. [Google Scholar]
27.Matias T, Dominski FH, Marks DF. Human needs in COVID-19 isolation. J Health Psychol. 2020;25: 871–882. 10.1177/1359105320925149 [DOI] [PubMed] [Google Scholar]
28.Jiménez-Pavón D, Carbonell-Baeza A, Lavie CJ. Physical exercise as therapy to fight against the mental and physical consequences of COVID-19 quarantine: Special focus in older people. Prog Cardiovasc Dis. 2020. 10.1016/j.pcad.2020.03.009 [DOI] [PMC free article] [PubMed] [Google Scholar]
29.Parouty J, Al Haddad H, Quod M, Leprêtre PM, Ahmaidi S, Buchheit M. Effect of cold water immersion on 100-m sprint performance in well-trained swimmers. Eur J Appl Physiol. 2010;109: 483–490. 10.1007/s00421-010-1381-2 [DOI] [PubMed] [Google Scholar]
30.Hug B, Heyer L, Naef N, Buchheit M, Wehrlin JP, Millet GP. Tapering for marathon and cardiac autonomic function. Int J Sports Med. 2014;35: 676–683. 10.1055/s-0033-1361184 [DOI] [PubMed] [Google Scholar]
31.Hnatkova K, Šišáková M, Smetana P, Toman O, Huster KM, Novotný T, et al. Sex differences in heart rate responses to postural provocations. Int J Cardiol. 2019;297: 126–134. 10.1016/j.ijcard.2019.09.044 [DOI] [PMC free article] [PubMed] [Google Scholar]

PLoS One. doi: 10.1371/journal.pone.0242303.r001

Decision Letter 0

Daniel Boullosa

1 Sep 2020

PONE-D-20-22573

Effects of COVID-19 lockdown on heart rate variability

PLOS ONE

Dear Dr. Bourdillon,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript by Oct 16 2020 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.
A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.
An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols

We look forward to receiving your revised manuscript.

Kind regards,

Daniel Boullosa

Academic Editor

PLOS ONE

Journal Requirements:

When submitting your revision, we need you to address these additional requirements.

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and

https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

2. Please note that PLOS does not allow reference to data not shown (stated at the end of the results section). Thus, before we proceed, we kindly ask you provide the relevant data within the manuscript, the Supporting Information files, or in a public repository. If the data are not a core part of the research study being presented, please remove any references to these data.

3. During our internal evaluation we noted that participants provided verbal consent, did the ethics committees/IRBs approve this consent procedure? Please explain: i) Why was written consent not obtained? ii) How did you record/document participant consent? Please provide these consent details in the ethics statement in the both the Methods section of the manuscript and in the online submission information.

4. Thank you for including your competing interests statement; "I have read the journal's policy and the authors of this manuscript have the following competing interests: Nicolas Bourdillon and Sasan Yazdani are employees of becare S.A."

5. Please upload a copy of Figure 3, to which you refer in your text on page 5. If the figure is no longer to be included as part of the submission please remove all reference to it within the text.

6. We note that you have included the phrase “data not shown” in your manuscript. Unfortunately, this does not meet our data sharing requirements. PLOS does not permit references to inaccessible data. We require that authors provide all relevant data within the paper, Supporting Information files, or in an acceptable, public repository. Please add a citation to support this phrase or upload the data that corresponds with these findings to a stable repository (such as Figshare or Dryad) and provide and URLs, DOIs, or accession numbers that may be used to access these data. Or, if the data are not a core part of the research being presented in your study, we ask that you remove the phrase that refers to these data.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Partly

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: No

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: No

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: In this paper, the authors investigated changes in heart rate variability before, during and after the lockdown which took place for about two months in France.

Data was collected according to standard procedure (morning test), and all typical metrics are ported, in the time (rMSSD) and frequency (LF HF) domains, for a decent sample of 95 individuals

Most importantly, subjective data was collected together with objective physiological data, which I find paramount in this case considering that despite what much of the literature reports, physiology needs to be contextualised with other variables, as exemplified by the fact that HRV could go either way (assuming a similar response for all individuals would be naive), and indeed this change does relate with the objective measurement of physiological stress derived via HRV analysis

The sample gets a bit small when stratified (e.g. only 5 women in the WB+ group), however as the changes are analysed relatively to their own historical data (baseline), I would consider this issue less problematic than in the case of comparing groups

My speculation for the lack of change in the standing position might be linked to the protocol, often the orthostatic measurement creates more issues than it tries to resolve, with individuals getting anxious or too worked up by the quick change of posture, which might result in the test itself just capturing that transitory readjustment, which has little to do with baseline physiological stress - which is what the test aims at capturing. It could be helpful in this case simply to do two separate tests, maybe separated by a few minutes, but this procedure is of course less practical. Unfortunately in the paper it is not clear if the protocol required a short period between the two phases (e.g. less than 30 seconds) or not, and therefore if this speculation makes sense. Please revise the paper including more information about the exact protocol, and also discuss this aspect if applicable at that point.

Interesting to see also how the change in ANS activity was rather stable during CFN

I understand that this is not the focus of the paper, but it would be relevant for practitioners and users of these technologies if the authors could speculate on what is behind the differences, why a smaller group felt better (which was reflected in their ANS) and why a larger group had more issues, any how this second group could potentially make changes in case another lockdown happens, to favore a more positive response

Given that the data was collected as part of other studies, I wonder if any other potential correlates were collected (physical activity apparently not), but anything else that could shed some light on factors behind these differences would be relevant)

In this context I find the discussion section quite limited by the focus on physical activity. In my experience, large changes in heart rate and rMSSD baseline are hardly associated to changes in physical activity alone, especially over rather short time periods and in healthy individuals, while psychological stressors might have a much larger impact. Given that the lockdown is clearly a huge psychological stressor, I would expect more discussion points around this aspect.

Note also how your own data seems to highlight how the psychological aspect is key (how are you feeling is the question, which does not seem to be tuned to physical activity), more than the physical activity aspect. Of course lack of physical activity as per se a strong psychological effect especially in previously active people, but then the conversation is not about de-training, it's again about psychological wellbeing when unable to perform physical activity. Hopefully this makes sense to the authors and the discussion can be extended to better cover these aspects, which of course are all speculative since no data has been collected on other covariates

Reviewer #2: The manuscript presents recordings of heart rate variability (HRV) and subjective well-being in a sample of French healthy adults before, during and after a period of strict confinement, imposed by the progression of the COVID-19 pandemic.

Using a subjective well-being metric as an independent variable, the psychophysiological response (measured by HRV indices recorded in different postures) was compared for groups and moments. Association between subjective well-being and HRV were also investigated.

The data recorded by the authors may present valuable and novel information regarding well-being and autonomic modulation of heart rate responses to a critical condition as the strict confinement experienced by the subjects of the sample. However, some analysis lacks justification (a priori) while other methodological issues deserve some attention. Also, the discussion and conclusions sound somewhat speculative or shallow.

In general, the study may present valuable contributions to the field, but some major adjustments are proposed hoping to contribute to the production of an even better manuscript.

Abstract

Considering the suggestions made in the methods and results sections that can significantly change the content of the manuscript body, it may not be worthwhile to address the abstract section in detail now. However, here are some suggestions:

I think that the readability could be improved if the acronyms (“BSL”, “CFN” and “RCV”) were placed next to the related terms. Since it is a personal impression, please, feel free to adopt or not that adjustment.

A brief sample characterization could be appreciable in this section, also a succinct presentation of the analysis made may help the reader to orient himself in relation to the reported results.

The acronyms “WB+” and “WB-” appear in the results without properly previous presentation. Please, provide a brief explanation for what they mean.

Its not clear in the abstract (as also in the manuscript body) of which moment (BSL, CFN, or RCV) the correlations refer to. Please, clarify that aspect.

Regarding the abstract conclusions, I suggest that the authors stick only to what the results allow to conclude. To assume that 20% of the subjects had an improvement in the autonomic status goes somewhat beyond the possibilities that the results of the manuscript allow. The changes in the average values of RMSSD and HR of the two groups in the three periods in which the recordings were made can reflect a number of things, including the return to a normal status, considering an anticipatory stress effect that would already be present in some individuals of the sample, in view of the progression of the COVID-19 disease in the world (which starts in December 2019). Also, the group division, without previous justification, anchored in a metric, apparently without prior validation, raises some concerns. In addition, the arbitrary determination of a value "> 2" as a cutoff point raises another concern. The conclusion is based mainly on the results that come as consequences of these decisions that were at first not justified, and this greatly weakens the assertiveness and weight of the sentences.

At the end of the adjustments resulting from this review, I suggest that the authors rethink the abstract and, if possible, adopt a more cautious language taking into account what can actually be concluded in view of the methodological characteristics and results presented by the study.

Introduction

PARAGRAPH 1:

The first part of the first paragraph develops well. When it states: “resulted in decreased physical activity”, I suggest adopting a more measured language. Although we agree that confinement may have resulted in a reduction in physical activity, the reference cited does not supports the statement as it is made. In the next sentence, data from the national institute “Santé Publique France” are presented, I suggest including this source properly in the references and then citing it. At the end of the first paragraph the authors mention that the period of confinement may have caused changes in “cardiovascular fitness and psychological states”, I suggest complementing this sentence with other references such as: Brooks et al., 2020 (https: //pubmed.ncbi.nlm. nih.gov/32112714/), and Wang et al., 2020 (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7084952/); as also mentioning the impact on metabolism and body composition (fat mass and free fat mass) among the possible consequences of confinement, as noted in Martinez-Ferran et al., 2020 (https://pubmed.ncbi.nlm.nih.gov / 32466598 /).

PARAGRAPH 2:

The first sentence of the second paragraph could be improved if the references cited were complemented, especially with regard to the exercise's ability to mitigate the psychological effects of confinement, since Pareja-Galeano (2015 - https: //pubmed.ncbi.nlm.nih. gov / 25730691 /) addresses in his letter to the editor the interaction between types of exercises and their possible effects specifically on the symptoms of depression in response to a study that investigates the relationship between PA and symptoms of depression in adolescents.

I also suggest to complement the second sentence of the same paragraph addressing applications of HRV in contexts and populations more related to the theme of the present study as in Thayer et al., 2010 (https://pubmed.ncbi.nlm.nih.gov/19910061/), Hynynen et al., 2011 (https://pubmed.ncbi.nlm.nih.gov/20972879/), Laborde et al., 2017 (https://pubmed.ncbi.nlm.nih.gov/28265249/), and Kim et al., 2018 (https://pubmed.ncbi.nlm.nih.gov/29486547/) in addition to athletes, as in the references already adopted.

Still on this paragraph, I suggest to rethink some sentences referring to the LF HRV index, in the light of the references suggested above, as well as those that follow: Goldberger 1999 (https://pubmed.ncbi.nlm.nih.gov/10199852/), Medeiros et al., 2018 (https://pubmed.ncbi.nlm.nih.gov/29619594/), and Hayano & Yuda 2019 (https://pubmed.ncbi.nlm.nih.gov/30867063/). Focusing the paragraph on the most reliable indexes and that present better physiological description such as RR, RMSSD and HF may provide a safer way to discuss the results. In addition, the part that refer to the use of HRV for performance related ends do not seems to have a direct connection with the theme of the study, please, better elucidate this connection or suppress that part.

Finally, the paragraph ends with a statement that cannot be supported by the cited reference, which presents only associations between HRV (adopted a priori as an indicator of stress) and measures of PA, Cardiorespiratory Fitness, and body composition. It is a cross-sectional study with a sample of men only, which is not a validation study and that does not involve investigating the reliability of HRV. This sentence must be rewritten, and other references can be adopted for this purpose (Thayer et al., 2010 https://pubmed.ncbi.nlm.nih.gov/19910061/; Kim et al., 2018 https: // pubmed. ncbi.nlm.nih.gov/29486547/).

PARAGRAPH 3:

I’m afraid that there is no evidence for expecting that part of the sample of the investigated population would “appreciate the confinement period”, it is difficult to conceive that this hypothesis could be postulated a priori. Please, provide a rationale for that, otherwise adjust that part.

Method

Please verify the first line of the study design subsection, it’s possible that the word “were” has been suppressed between the words “rules” and “applied”, verify if that sentence is correctly worded.

Experimental design:

I’m afraid that some information regarding the study design are missing in that subsection, while some are placed in other subsections and may better apply to the current. I would suggest the authors to offer a broader and clearer description of the study. Please, in addition to the information regarding the HRV recording periods state the other metrics adopted (VAS) and a concise declaration of the analyses made with those metrics (e.g. that the moments were compared and associations were tested) to better guide readers through the manuscript section.

Participants:

Have the authors a good reason to not include subjects with more than 60 years of age? It would be interesting provide a rationale to that age range inclusion criteria adoption. Also, regarding the inclusion criteria, please explain how the data was collected, clarify which criteria were just declared by the participants and which were really measured. Please, justify or clarify why at least forty orthostatic tests were adopted as inclusion criteria during the period of the study, if a total of just thirty where necessary, as you used 10 tests in each period for comparisons.

Heart rate variability:

Since the inter-beat intervals (IBI) were self-recorded, please, state explicitly what instructions were given to participants and if any prior training has been offered for the subjects to properly perform the IBI recordings. Please, include the validation studies regarding the IBI recording devices and for the smartphone app adopted for the IBI recording. Otherwise, mention that in the study limitations.

Regarding the artifact corrections, please, declare if any error percentage were adopted as exclusion criteria for IBI recordings and which error percentage it was. Otherwise, provide a rationale for it, since some error percentages may profoundly affect the reliability of the IBI recording and resulting HRV values (Peltola, 2012 https://pubmed.ncbi.nlm.nih.gov/22654764/). Please, also declare the recording time window adopted in each position for the HRV indices calculation and, if some stabilization period was adopted, include that information too.

Finally, please, state how did you handled with the following aspects that could acutely interfere in the HRV recordings: alcohol consumption, quality and duration of sleep, effects of vigorous exercises and other known factors. If those issues were not properly addressed, please, declare in the study limitations.

Visual analogic scale:

Please, provide the validation study that support the adopted well-being metric. Otherwise, mention that in the study limitations. Also, clarify what means the graduation values 0 to 10 that the VAS referred to, and declare if the subjects received any prior training to use that mobile application.

Statistical Section

Importantly: Regarding the group effect division adopted here (“WB+” and “WB-”), no rationale or justification was presented a priori for that division. So, the authors must explain in the manuscript why that division was adopted, which criteria were adopted for the group division and justify them, preferably based on the subject literature. I would like to add that some other group divisions, more evidently justifiable by literature, as by age clusters or by sex could be made instead of the adopted by the authors, since Brooks et al., 2020 (cited in the present manuscript references) highlighted that gender and age may be predictors of negative psychological impacts of quarantine and Hnatkova et al., 2019 (https://pubmed.ncbi.nlm.nih.gov/31611089/) showed that heart rate responses to postural changes may be different for sex.

Please, present the statistical power achieved with that sample for the analysis used.

The authors must declare if unitary or averaged values of the individuals HRV recordings were adopted in the different moments (BSL, CFN and RCV) for the comparisons made in the two-way ANOVA analysis. Also, regarding both metrics (HRV and VAS), clarify which values (unitary or averages) and of which moments (BSL, CFN and RCV) were adopted for the calculation of Pearson’s correlation coefficient. Please, provide information in a more detailed way in this topic, if possible.

Results

If some data is placed in tables it could improve that section.

Please, present the HR and HRV indices means in each period (BSL, CFN and RCV) per condition (SU and ST). Please, present the correct units in the figures 1 and 2. Also, in figure legends state of which recording positions they refer to.

Figure 3 is missing. Regarding the correlations, please clarify the points above mentioned in methods section. If correlations were traced in each one of the moments (BSL, CFN and RCV), please, present all Pearson’s correlation coefficients and respective confidence intervals, if possible. I would also suggest a regression analysis combining FC and HRV indices, since there are some interactions between those variables that can highlight or suppress the observable psychophysiological effects of interest (De Geus et al., 2018 https://pubmed.ncbi.nlm.nih.gov/30357862/)

Discussion

Most parts of discussion refer to the unjustified group division made by the authors and to a survey relating to behavioral aspects during lockdown as Physical Activity (PA) and exercise, that were not measured or controlled in the present investigation, while the interesting association between VAS and HRV indices was barely discussed. I would like to suggest to the authors a deeper and less speculative discussion, preferably based on the literature pointed out in the introduction and along of the reviewer suggestions.

Limitations

In addition to the limitations pointed out in other sessions, it would be prudent to comment that factors that may be associated with HRV or modulate their interactions with different stressors have not been controlled, such as: Body composition (Esco et al., 2011 https: //pubmed.ncbi.nlm .nih.gov / 21691230 /; Yi et al., 2013 https://pubmed.ncbi.nlm.nih.gov/23225799/), Cardiorespiratory Fitness (Buchheit & Gindre, 2006 https: //pubmed.ncbi.nlm. nih.gov/16501030/; Kiviniemi et al., 2017 https://pubmed.ncbi.nlm.nih.gov/29135784/) and others.

Conclusion

Some parts of the conclusion sound speculative or walk beyond the possibilities of the study results. Please, considering the reviewer suggestions in the sections above, rethink that section too.

References

Please adjust reference number two accordingly.

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

PLoS One. 2020 Nov 12;15(11):e0242303. doi: 10.1371/journal.pone.0242303.r002

Author response to Decision Letter 0

29 Sep 2020

Reviewer #1: In this paper, the authors investigated changes in heart rate variability before, during and after the lockdown which took place for about two months in France.

We thank you for reviewing our manuscript and for providing comments and suggestions that have helped us to improve it. We have considered your remarks and made amendments when necessary in the revised manuscript. We appreciate your further perusal of the revised manuscript.

We have provided our responses to your comments that are in bold. Amended sentences are in italic with the additional wordings in red.

Data was collected according to standard procedure (morning test), and all typical metrics are ported, in the time (rMSSD) and frequency (LF HF) domains, for a decent sample of 95 individuals

Thank your for this comment, indeed we designed the analysis so that each individual is his own baseline which minimizes the potential bias when the groups have unbalanced number.

My speculation for the lack of change in the standing position might be linked to the protocol, often the orthostatic measurement creates more issues than it tries to resolve, with individuals getting anxious or too worked up by the quick change of posture, which might result in the test itself just capturing that transitory readjustment, which has little to do with baseline physiological stress - which is what the test aims at capturing. It could be helpful in this case simply to do two separate tests, maybe separated by a few minutes, but this procedure is of course less practical. Unfortunately, in the paper it is not clear if the protocol required a short period between the two phases (e.g. less than 30 seconds) or not, and therefore if this speculation makes sense. Please revise the paper including more information about the exact protocol, and also discuss this aspect if applicable at that point.

Thank you for this comment. The transition between the supine and standing phases was a few seconds (typically between 3 and 8 seconds). We agree that the standing phase induces a lot more issues than the supine one, but in our view (and before the pandemic crisis broke out) the supine phase is designed to assess the baseline physiological stress while the standing phase is designed to check for lack of activation of the sympathetic system or lack of withdrawal of the parasympathetic system. It is not designed to assess baseline physiological stress. For clarity, we added the following sentences in the Methods section in the manuscript:

Interesting to see also how the change in ANS activity was rather stable during CFN

Thank you for this suggestion. The factors influencing a positive or negative response to lockdown are numerous, complex, and often interact between each other. In addition, most factors are out of hands of the practitioners. We can only speculate that encouraging physical activity (but still respecting the lockdown rules) even simply walking and reassuring the population with regards to the numerous stressors (financial loss, fear of infection, lo of social activities etc.) may be the most effective ways to counteract the deleterious effects of lockdown.

Thank you for this excellent suggestion, but unfortunately, we do not have anything substantial that could shed light on the factors explaining the differences between the groups. The strict lockdown made impossible any visit to the laboratory so that no complementary measures were recorded.

We added the following paragraph in the discussion section:

Beyond this speculative influence of physical activity, there are many stressors during lockdown [2]: subjective (i.e., poor information on the duration of the lockdown, the fears of infection, frustration and boredom, sense of isolation, anger , guilt, helplessness, loneliness, nervousness, sadness) or objective (i.e., inadequate supplies, financial concerns, altered usual day-to-day activities etc.) sources of stress have an impact on psychological outcomes and indirectly on HRV.

We entirely agree with these suggestions, we have added the following in the discussion section

In general, the study may present valuable contributions to the field, but some major adjustments are proposed hoping to contribute to the production of an even better manuscript.

We have provided our responses to your comments that are in bold. Amended sentences are in italic with the additional wordings in red.

Abstract

Thank you for this suggestion the abstract now reads:

…on a regular basis before (BSL), during (CFN) and after (RCV) the lockdown.

A brief sample characterization could be appreciable in this section, also a succinct presentation of the analysis made may help the reader to orient himself in relation to the reported results.

95 participants were included in this study (27 women, 68 men, 37 ± 11 years, 176 ± 8 cm, 71 ± 12 kg),

The acronyms “WB+” and “WB-” appear in the results without properly previous presentation. Please, provide a brief explanation for what they mean.

the methods section of the abstract now reads

The participants were split in two groups, those who reported an improved well-being (WB+, increase >2 in VAS score) and those who did not (WB-) during CFN.

Its not clear in the abstract (as also in the manuscript body) of which moment (BSL, CFN, or RCV) the correlations refer to. Please, clarify that aspect.

You are right. We modified the abstract as follows:

When pooling data of the three phases, there was a moderate significant correlation

New paragraph was also added in the manuscript body:

Correlations

Correlations were computed for LF, HF, HR and RMSSD against VAS, in the supine and the standing positions, regardless of the time points (BSL, CFN and RCV), which means that all data points were pooled when computing the correlations. Correlations were made using MATLAB® (R2019a, MathWorks, Natick, MA, USA)

We entirely agree with this suggestion and we have turned down the tone of the discussion and conclusion accordingly.

Also, the group division, without previous justification, anchored in a metric, apparently without prior validation, raises some concerns. In addition, the arbitrary determination of a value "> 2" as a cutoff point raises another concern. The conclusion is based mainly on the results that come as consequences of these decisions that were at first not justified, and this greatly weakens the assertiveness and weight of the sentences.

You are right. We toned down our conclusion.

As recommended, we modified the conclusion of the abstract, as follows:

The observed recordings may reflect a large variety of responses (anxiety, anticipatory stress, change on physical activity…) beyond the scope of the present study. However, these results confirmed the usefulness of HRV as a non-invasive means for monitoring well-being and health in the general population

Introduction

PARAGRAPH 1:

Thank you for those very relevant suggestions, first paragraph now reads

, may have resulted in decreased physical activity.

[…]

. Beyond these self-declared data, the impact of the lockdown period remains unclear, strong psychological impacts have been reported in a review [2] and specifically to the COVID-19-related lockdown [3], as well as metabolic and body composition outcomes [4], but one may hypothesize that it may have led to changes in cardiovascular fitness and psychological states.

PARAGRAPH 2:

The beginning of paragraph 2 now reads:

Exercise plays a fundamental role in cardiovascular health [5] but also in mitigating the psychological impacts of lockdown [6]. Aerobic exercises such as walking or endurance running appears to be more beneficial than sprint running or force/power exercises [6,7].

The sentence now reads:

Heart rate variability (HRV) is a commonly used method for cardiovascular follow-up in athletes [8], healthy people [9] cardiovascular patients [10], and is related to self-regulations at the cognitive, emotional, social and health levels [11,12].

We agree and have modified the paragraph as follows:

Specifically, HRV analysis allows to evaluate the modulation of the sympathetic and parasympathetic branches of the autonomic nervous system. The low-frequency (LF) band reflects a mix of sympathetic and parasympathetic modulations on the heart [13] and has been proposed as an index of the sympathovagal balance [14]. The migration of the respiratory sinus arrhythmia in the low-frequency band is a subject of debate [15], which leaves the physiological implications of this frequency band unclear [16,17]. Respiratory sinus arrhythmia is the main phenomenon provoking changes in the HF band and RMSSD which therefore mainly reflects parasympathetic influences on the heart [18].

In addition, the part that refer to the use of HRV for performance related ends do not seems to have a direct connection with the theme of the study, please, better elucidate this connection or suppress that part.

The sentences and references linked to performance have been removed

Finally, HRV-based methods may be used to assess autonomic imbalances, diseases [10], stress and well-being [12].

PARAGRAPH 3:

Please provide an adequate justification for the present study. Adopt also a more cautious language regarding the objectives since the methods and other characteristics of the study do not allow some of the author's purpose objectives. I’m afraid that there is no evidence for expecting that part of the sample of the investigated population would “appreciate the confinement period”, it is difficult to conceive that this hypothesis could be postulated a priori. Please, provide a rationale for that, otherwise adjust that part.

We followed your recommendations modified the hypotheses.

We hypothesized that alteration in parasympathetic-related markers (i.e., decreases in RMSSD and HF, increase resting HR) would reflect a negative feeling over the period, whilst a minority of the population would report an improved subjective feeling with consequences on HRV, potentially in line with the report by Santé Publique France [1].

Method

Strict lockdown (further denoted CFN) rules were applied in France over 8 weeks, from 17 March to 11 May 2020.

Experimental design:

For clarity, we added detailed information in the ‘methods’ section

Nevertheless, data collection was performed for the purpose of this study, using recording devices distributed to the participants before the lockdown. The equipment consisted of a RR-interval-measuring chest strap and a dedicated mobile application that recorded both RR intervals from the strap and a declared visual analogic scale (VAS).

Participants:

Have the authors a good reason to not include subjects with more than 60 years of age? It would be interesting provide a rationale to that age range inclusion criteria adoption.

As stated in the manuscript, the lockdown was unexpected, the participants were equipped with the devices for other purposes than this study in the first place. The initially planned studies involved physical exercises with a maximum age for inclusion criteria of 60 years-old to limit the cardiovascular risks. We agree that it is a limitation regarding the effect of COVID-lockdown.

Also, regarding the inclusion criteria, please explain how the data was collected, clarify which criteria were just declared by the participants and which were really measured.

Please, justify or clarify why at least forty orthostatic tests were adopted as inclusion criteria during the period of the study, if a total of just thirty where necessary, as you used 10 tests in each period for comparisons.

From January 1st to May 11th (end of lockdown) there were 20 weeks. At 2 tests per week in average makes 40 tests to have a reasonable follow-up. In addition, if all the tests were performed in one of the three periods (baseline for example) there was no point comparing the periods, hence our additional criteria for at least 10 tests in each period, again to have a reasonable follow-up.

Heart rate variability:

The H7 is the most used RR-recording device, the TP5+ uses the exact same technology:

Comparison of Heart-Rate-Variability Recording With Smartphone Photoplethysmography, Polar H7 Chest Strap, and Electrocardiography. Daniel J Plews, Ben Scott, Marco Altini, Matt Wood, Andrew E Kilding, Paul B Laursen. Int J Sports Physiol Perform. 2017 Nov 1;12(10):1324-1328. doi: 10.1123/ijspp.2016-0668. DOI: 10.1123/ijspp.2016-0668

The smartphone application is just a Bluetooth receiver, using the standard BLE protocol, which does not interfere in any ways with the recording. It is just a wireless system. The results would have been exactly the same if the RR intervals had been stored on the smartphone memory and downloaded to a computer using a wire. https://web.archive.org/web/20170130085524/https://www.bluetooth.com/specifications/bluetooth-core-specification

Our quality check goes beyond just having the number/percentage of artifacts, it uses other measures such as closeness of the artifacts, etc. In any case the quality of the signals was checked to ensure that artifacts did not drastically affect the extracted HRV parameters. Those are in-house algorithms under patenting process; therefore, we cannot disclose in detail how they work.

Out of each of the 5-minute periods, the first minute was used as a stabilization period and was excluded from the analysis whilst the last four minutes were analyzed for HRV.

Through questionnaire in the application and for each test, participants declared their potential lack of sleep, alcohol consumption (as limited as possible), digestive problems and other potential confounding factors that may have modified the HRV parameters reported in this study. Those factors are known as key in HRV and well-being alterations and may partly explain the cardiovascular deconditioning observed. However, in the present study, we did not find any factor that may have explained the differences between the two groups.

Visual analogic scale:

VAS is a widely used tool electronically

Visual analogue scales (VAS): Measuring instruments for the documentation of symptoms and therapy monitoring in cases of allergic rhinitis in everyday health care

Position Paper of the German Society of Allergology (AeDA) and the German Society of Allergy and Clinical Immunology (DGAKI), ENT Section, in collaboration with the working group on Clinical Immunology, Allergology and Environmental Medicine of the German Society of Otorhinolaryngology, Head and Neck Surgery (DGHNOKHC). Allergo J Int. 2017; 26(1): 16–24. doi: 10.1007/s40629-016-0006-7

Becare S.A. employees controlled that the participants properly used the mobile application and chest belt and responded quickly to any question from the participants using dedicated chat bots, emails or telephone.

Statistical Section

We adopted the criteria of change in VAS >2, that corresponded to 20% change in the scale. We expected with such a large change to lower the intra-individual variability. As explained in ‘methods’, the analysis is based on a large number of records.

Another important limitation of the present study is that our sample did not allow any other group divisions, evidently justifiable by literature, as by age clusters or gender that may be predictors of negative psychological impacts of lockdown. Moreover, Hnatkova et al. [27] showed that heart rate responses to postural changes may be different for sex.

I would like to add that some other group divisions, more evidently justifiable by literature, as by age clusters or by sex could be made instead of the adopted by the authors, since Brooks et al., 2020 (cited in the present manuscript references) highlighted that gender and age may be predictors of negative psychological impacts of quarantine and Hnatkova et al., 2019 (https://pubmed.ncbi.nlm.nih.gov/31611089/) showed that heart rate responses to postural changes may be different for sex.

We would have liked to be able to conduct such studies grouping age, gender and postural changes. But that required to have a priori groups matched for those parameters which obviously we did not have as the lockdown was unexpected. As stated in the limitations section, despite we had no prior intention to study the lockdown and failed to have such evenly constituted groups, we feel like we have a dataset that still shows some interesting results which should be brought to the readers. We added the following sentences in ‘limitations’ section

Another important limitation of the present study is that our sample did not allow any other group divisions, evidently justifiable by literature, as by age clusters or gender that may be predictors of negative psychological impacts of quarantine. Moreover, Hnatkova et al. (2019) showed that heart rate responses to postural changes may be different for sex.

Please, present the statistical power achieved with that sample for the analysis used.

Statistical power was added in the result section.

ANOVA analyses were carried out on unitary values (i.e. no average per period or otherwise). Pearson’s correlation coefficients analyses were carried out on unitary values (i.e. no average per period or otherwise).

Results

If some data is placed in tables, it could improve that section.

Figures 1 and 2 have been updated to also show the standing position. Units of the figures are normalized with respect to baseline as stated in the statistics section.

HR and HRV units were normalized with respect to BSL.

Figures legends have been updated to indicate the position.

Apologies, Figure 3 never existed. Table 1 has been added with all Pearson’s coefficient values.

I would also suggest a regression analysis combining FC and HRV indices, since there are some interactions between those variables that can highlight or suppress the observable psychophysiological effects of interest (De Geus et al., 2018 https://pubmed.ncbi.nlm.nih.gov/30357862/)

Here are the Pearson’s correlation data of HRV vs. HR data

R p CI

LF SU -0.22 <0.01 -0.35 -0.08

HF SU -0.31 <0.01 -0.49 -0.10

RMSSD SU -0.52 < 0.001 -0.61 -0.41

LF ST 0.12 0.10 -0.02 0.25

HF ST 0.03 0.70 -0.11 0.17

RMSSD ST -0.28 < 0.001 -0.40 -0.15

We believe that there is no need to show this table in the manuscript. However, if the reviewer asked for its inclusion, we would do it

Discussion

We fully agree and acknowledge your relevant suggestions that help to improve the manuscript.

We toned down the influence of physical activity. We deleted the following sentences:

These lifestyles and behaviors included a given level of physical exercise to maintain an adequate health status [23], and guarantee an active aging by reducing the risk associated diseases in older people [24].

In the present study, 80% of the participants reported an increased HR associated to decreased RMSSD and increased LF: these changes could be the consequences of a cardiovascular detraining, with decreased parasympathetic influences on the heart. The loss of outdoor activities as walking is likely of clinical importance since lockdown accelerates vicious circles between isolation, lack of physical activity, psychological stress/anxiety and impaired immunity [27]. Meanwhile, the participants had more time to exercise, but they had to do it by themselves, based on their personal knowledge and material possibilities, with extremely limited external advises and totally absent group motivation.

We also added the following paragraph on the psychological outcomes

Beyond this speculative influence of physical activity, there are many stressors during quarantine [2] : subjective (i.e., poor information on the duration of the quarantine, the fears of infection, frustration and boredom, sense of isolation, anger , guilt, helplessness, loneliness, nervousness, sadness) or objective (i.e., inadequate supplies, financial concerns, altered usual day-to-day activities..) sources of stress have an impact on psychological outcomes and indirectly on HRV.

Limitations

We have modified the ‘limitations’ section as follows:

Another important limitation of the present study is that our sample did not allow any other group divisions, evidently justifiable by literature, as by age clusters or gender that may be predictors of negative psychological impacts of quarantine. Moreover, Hnatkova et al. (2019) showed that heart rate responses to postural changes may be different for sex.

Conclusion

Some parts of the conclusion sound speculative or walk beyond the possibilities of the study results. Please, considering the reviewer suggestions in the sections above, rethink that section too.

We modified the conclusion as follows:

References

Please adjust reference number two accordingly.

Reference adjusted (now reference #1)

Further to the email sent to you from the academic editor, please accept our sincere apologies but request number 4 was incomplete. It should have read;

Thank you for including your competing interests statement; "I have read the journal's policy and the authors of this manuscript have the following competing interests: Nicolas Bourdillon and Sasan Yazdani are employees of becare S.A."

We note that one or more of the authors are employed by a commercial company: becare S.A.

1. Please provide an amended Funding Statement declaring this commercial affiliation, as well as a statement regarding the Role of Funders in your study. If the funding organization did not play a role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript and only provided financial support in the form of authors' salaries and/or research materials, please review your statements relating to the author contributions, and ensure you have specifically and accurately indicated the role(s) that these authors had in your study. You can update author roles in the Author Contributions section of the online submission form.

Please also include the following statement within your amended Funding Statement.

“The funder provided support in the form of salaries for authors [insert relevant initials], but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.”

If your commercial affiliation did play a role in your study, please state and explain this role within your updated Funding Statement.

2. Please also provide an updated Competing Interests Statement declaring this commercial affiliation along with any other relevant declarations relating to employment, consultancy, patents, products in development, or marketed products, etc.

Within your Competing Interests Statement, please confirm that this commercial affiliation does not alter your adherence to all PLOS ONE policies on sharing data and materials by including the following statement: "This does not alter our adherence to PLOS ONE policies on sharing data and materials.” (as detailed online in our guide for authors http://journals.plos.org/plosone/s/competing-interests) . If this adherence statement is not accurate and there are restrictions on sharing of data and/or materials, please state these. Please note that we cannot proceed with consideration of your article until this information has been declared.

Please include both an updated Funding Statement and Competing Interests Statement in your cover letter. We will change the online submission form on your behalf.

Please know it is PLOS ONE policy for corresponding authors to declare, on behalf of all authors, all potential competing interests for the purposes of transparency. PLOS defines a competing interest as anything that interferes with, or could reasonably be perceived as interfering with, the full and objective presentation, peer review, editorial decision-making, or publication of research or non-research articles submitted to one of the journals. Competing interests can be financial or non-financial, professional, or personal. Competing interests can arise in relationship to an organization or another person. Please follow this link to our website for more details on competing interests: http://journals.plos.org/plosone/s/competing-interests

We apologise for any confusionn this has caused and look forward to receiving your revised manuscript,

Attachment

Submitted filename: Reviewer comments.docx

Click here for additional data file.^{(63.8KB, docx)}

PLoS One. doi: 10.1371/journal.pone.0242303.r003

Decision Letter 1

Daniel Boullosa

26 Oct 2020

PONE-D-20-22573R1

Effects of COVID-19 lockdown on heart rate variability

PLOS ONE

Dear Dr. Bourdillon,

Please submit your revised manuscript by Dec 10 2020 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.
A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.
An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

We look forward to receiving your revised manuscript.

Kind regards,

Daniel Boullosa

Academic Editor

PLOS ONE

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: (No Response)

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: Yes

Reviewer #2: Partly

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

Reviewer #1: Yes

Reviewer #2: No

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

Reviewer #1: Yes

Reviewer #2: Yes

**********

6. Review Comments to the Author

Reviewer #1: All my concerns have been addressed in the updated version of the manuscript, I do not have any further comments

Reviewer #2: Firstly, I would like to congratulate the authors by their effort in providing clarifications and incorporating adjustments throughout the manuscript.

Most of the issues previously pointed were solved, although some of them were not fully clarified. Considering that, I tried to be more specific in some requests and reinforced the importance of them for the higher quality possible of this manuscript.

Some minor aspects not highlighted in the previous review were pointed now, but mostly as suggestions for a better readability of the manuscript.

Methods section still brings me some concern, but I hope that with authors adjustments and clarifications we will turn that section even better.

Dear author,

Find below my review of your revised manuscript, divided by section:

Abstract

The adjustments made in the abstract were well done, congratulations.

However, I added some points that still needs attention, that follows:

I suppose that adjusting the following sentence to the plural would be appropriate:

“there was a moderate significant correlation between VAS and HR, RMSSD, HF, respectively, in the supine position”

Also, I noted that is a significant correlation between standing RMSSD and VAS present in table 1. Comments about that result are missing in the abstract and throughout the manuscript. Finally, I also suggest you to suppress the term “moderate” of the above affirmation or provide, for the readers (in the manuscript body), the parameters you adopted for that qualitative interpretation of the Pearson’s correlation coefficient.

Regarding the abstract’s conclusion I would suggest you rethink the ending of the final sentence, especially considering that, although broad, your sample may not represent the general population. In my opinion, simply changing “in the general population” to “in this population” may solve this issue.

Introduction

PARAGRAPH 1:

The adjustments made in the first paragraph are well done.

PARAGRAPH 2:

Regarding the second paragraph, the quotations on the first sentence (references 6 and 7) remains not supporting the affirmations as they are. However, you may solve that issue simply, including “some of the possible” after: “…but also in mitigating”; and adding “ In those cases” before: “Aerobic exercises such as walking or endurance…”. Or another way, feel free.

The second paragraph part referring to HRV indexes was really improved.

But the sentences referring to the LF HRV index still needs a little adjustment. Since band migration of the RSA is not the only issue regarding the physiological meaning of LF, I would suggest you complement the text alerting the readers about that. Also, please complement the quotation of the sentence that refers to HF and RMSSD, Reference 18 only supports the HF index physiological meaning, but not RMSSD index meaning.

Also, please, better clarify for the readers what are you trying to say with “of one or the other” in the following sentence: “Hypotonia of one or the other is a sign of cardiovascular deconditioning”. Or you may suppress “of one or another”, as the sentence “Hypotonia is a sign of cardiovascular deconditioning” sustain the idea of the previous sentence and reads better, in my opinion.

PARAGRAPH 3:

In the third paragraph the hypothesis adjustment was all right. However, the study still lacks an explicit justification, and the second aim is a little over tuned. But I think that there is no need to jeopardize the publication by focusing on this points more related to my perception. So, I will let those observations for your reflexion.

Method

Most of the adjustments made in Methods section are all right. However, some aspects still brings me concern.

Participants:

Thank you for the explanation about the age range of your sample.

To explicitly declare some information like that, in this section of the manuscript, can improve the comprehension of methodological processes that may not be obvious for the reader. So, please, consider to include something like the sentence that you wrote in the response letter: “… The initially planned studies involved physical exercises with a maximum age for inclusion criteria of 60 years-old to limit the cardiovascular risks”; or another similar statement. That would be fine.

Still regarding inclusion criteria, a request was not fully clarified. So, I will try to be more specific: You state that “physically active, healthy, non-smokers, with no known diseases and no pregnancy or lactation for women” subjects composed the sample. If all those data were self-declared, please, make a statement on the manuscript clarifying it. Or, if, for example, physical activity or health were measured by accelerometry or (previous to the pandemic state) physical examination, respectively, you may report which data was declared and which was measured, and how it was done.

Thank you for the explanation regarding the adoption of forty tests instead of thirty. Please, consider incorporating on the manuscript body part of the explanation provided in the response letter. Explicitly declaring some methodological decisions like those could reinforce the quality of your work, for the readers.

Heart rate variability:

Thank you for the information about the HRV measurement devices.

Please, make a quoted statement on the manuscript body about the validity of the adopted HRV measurement devices. You may simply adjust part of the following explanation provided in the response letter and concisely incorporate it to the manuscript:

“The H7 is the most used RR-recording device, the TP5+ uses the exact same technology:

Comparison of Heart-Rate-Variability Recording With Smartphone

Photoplethysmography, Polar H7 Chest Strap, and Electrocardiography. Daniel J

Plews, Ben Scott, Marco Altini, Matt Wood, Andrew E Kilding, Paul B Laursen. Int J

Sports Physiol Perform. 2017 Nov 1;12(10):1324-1328. doi: 10.1123/ijspp.2016-

0668. DOI: 10.1123/ijspp.2016-0668

The smartphone application is just a Bluetooth receiver, using the standard BLE

protocol, which does not interfere in any ways with the recording. It is just a wireless

system. The results would have been exactly the same if the RR intervals had been

stored on the smartphone memory and downloaded to a computer using a wire.

https://web.archive.org/web/20170130085524/https://www.bluetooth.com/specificatio

ns/bluetooth-core-specification”

Regarding the artifact corrections, please, state in the manuscript body that your app uses filtering algorithms not available to the public that were applied in that process, since that information may impact the replicability of your data.

Visual analogue scale:

Thank you for the complement to the manuscript about the remote support provided to the subjects. I also agree that VAS is a widely used tool. However, the way that your VAS was presented in the manuscript lacks some important information. I’m afraid that “their sensation of the moment”, as you state in some point, is a poor description and may have several meanings beyond the intended in the present study.

An adequate presentation of that psychometric instrument needs a more detailed description in the methods to ensure an adequate replicability of your study. So, I would like to suggest you report in this subsection of the methods some aspects as the anchor question, and the values on the horizontal line extremes, that are missing. Please, provide and incorporate to the manuscript a more detailed description of that psychometric instrument (VAS) that you adopted, since as states the article provided by the authors in the response letter: “The most important aspect of any VAS however is the question that is combined to it and not the line. The line remains the same, but the question may change.”.

Correlations:

Thank you for the inclusion of the information in this subtopic. That subtopic should be part of the Statistics subtopic, on my opinion. Also, please, clarify if you tested LF and HF in absolute units or normalized units, or both. If both were tested, you need to include the results of both in table 1.

Statistics Section

Thank you for the explanation regarding the choice of a change in VAS>2 as a criterion adopted for the group division. Concisely reporting that information in the manuscript body may improve the presentation of your method section for the reader.

Adjustments made in the manuscript regarding the other possible group divisions are well done.

Regarding the statistical power, in addition to presenting values you must declare in the statistical section which way you took to find those values. Please, clarify for the reader how those statistical power values were calculated.

I would like to add that the requests regarding statistical power, in that and in the previous review, were made to add robustness to your method, since the amount of data collected seems to ensure a high statistical power. So, adequately presenting that information in the methods (for both tests: ANOVA and Pearson’s correlation) could highlight a valuable aspect of your manuscript.

Results

Although partially complete, the previous requests regarding results section were well done.

Please, present in the manuscript the HR and HRV mean values (and SD) of the sample, in each recording position per period (BLS, CFN, and RCV) and per group in each period.

I also noted that a significant correlation between RMSSD and VAS was present in standing position (table 1), but the manuscript only mentions and discuss the associations observed in supine position. Please, adjust that throughout the text.

Thank you for your consideration about the interactions between HR and HRV. In my opinion, just reporting the mean values of HR and HRV in each position and per period could provide sufficient information for the reader.

Please, clarify which of the reported results of LF and HF are referent to absolute units, and which are referent to normalized units, as you mention that both were calculated in the methods section. In case of using only one of those, I suggest you present in methods section only what was analyzed and reported in results section.

Discussion

Thank you for considering the previous suggestions and for incorporate them in your discussion. However, I would now suggest you some minor and more specific adjustments in your discussion since I have made just a shallow approach to that part of the manuscript in my previous review:

At the ending of the second paragraph of the discussion I suggest you to be cautious with some affirmations. With that in mind, please, adjust the following sentence: “In this increasing well-being, the fact that increased RMSSD, LF and HF (associated to decreased HR) were also observed post lockdown, is a marker of an effective and lasting improvement in cardiovascular fitness.” I suggest you change “is” to “may be” before “a marker” and to change “cardiovascular fitness” to “cardiovascular health”. Also, in the subsequent sentence, I suggest you adopt other expression instead of “performance”, it may sound out of context, since the paragraph is not talking about entrainment or performance specifically, but in part about physical activity, that is a broader concept.

In the beginning of the fourth paragraph, I suggest you adjust the sentence to the plural and suppress the term “moderate”, in case you don’t have provided any parameter for that qualitative interpretation of the Pearson’s correlation coefficient previously in the manuscript. Also, please, discuss the significant correlation between VAS and RMSSD observed in standing position.

Limitations:

This section was really improved. Congratulations.

Please, change “is” to “was” in the following sentence of the limitations: “The separation criterion between the WB+ and WB- groups is arbitrary”.

Conclusion

The adjustments made in conclusion were nice. Congratulations.

In my opinion, changing: ”general cardiovascular detraining” to “cardiovascular health” may provide to the reader a more assertive sentence. Feel free to incorporate or not that suggestion.

Regarding the last sentence of the conclusion, please rethink the term “general population”, especially considering that, although broad, your sample may not represent the general population. In my opinion, simply changing “in the general population” to “in this population” may solve this issue.

Table 1:

Please report the measurement units of HR and HRV indexes in the first column of table 1.

Figures 1 and 2:

Figure legends describe the following symbols: “* p < 0.05 for difference with

BSL. # p < 0.05 for difference with CFN.”. However, in the figures 1 and 2 the symbols are one or two asterisks “*” or “(**)”. Please, clarify what the two asterisks symbol means.

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

PLoS One. 2020 Nov 12;15(11):e0242303. doi: 10.1371/journal.pone.0242303.r004

Author response to Decision Letter 1

28 Oct 2020

Reviewer #2: Firstly, I would like to congratulate the authors by their effort in providing clarifications and incorporating adjustments throughout the manuscript.

Some minor aspects not highlighted in the previous review were pointed now, but mostly as suggestions for a better readability of the manuscript.

Methods section still brings me some concern, but I hope that with authors adjustments and clarifications we will turn that section even better.

We have provided our responses to your comments that are in bold. Amended sentences are in italic with the additional wordings in red.

Dear author,

Find below my review of your revised manuscript, divided by section:

Abstract

The adjustments made in the abstract were well done, congratulations.

However, I added some points that still needs attention, that follows:

I suppose that adjusting the following sentence to the plural would be appropriate:

“there was a moderate significant correlation between VAS and HR, RMSSD, HF, respectively, in the supine position”.

Done

Also, I noted that is a significant correlation between standing RMSSD and VAS present in table 1. Comments about that result are missing in the abstract and throughout the manuscript.

Thank you for this relevant comment. We modified the sentence as follows:

In standing position, HRV parameters were not modified during CFN but RMSSD was correlated to VAS.

Finally, I also suggest you to suppress the term “moderate” of the above affirmation or provide, for the readers (in the manuscript body), the parameters you adopted for that qualitative interpretation of the Pearson’s correlation coefficient.

Done

Introduction

PARAGRAPH 1:

The adjustments made in the first paragraph are well done.

Thank you!

PARAGRAPH 2:

We followed your relevant suggestions. The sentences are now:

The second paragraph part referring to HRV indexes was really improved.

The migration of the respiratory sinus arrhythmia in the low-frequency band is a subject of debate [15], and it is not the only issue regarding the physiological meaning of LF [16], which leaves the physiological implications of this frequency band unclear [17].

Also, please complement the quotation of the sentence that refers to HF and RMSSD, Reference 18 only supports the HF index physiological meaning, but not RMSSD index meaning.

We have added the reference to the task force (1996) to help the readers to understand the physiological meaning of RMSSD.

We modified the sentence as suggested.

PARAGRAPH 3:

You are right. We toned down the sentence as follows:

..and to investigate whether changes in HRV were related to some changes in psychological states during and after this period.

Method

Most of the adjustments made in Methods section are all right. However, some aspects still brings me concern.

Participants:

Thank you for the explanation about the age range of your sample.

Thank you again for this excellent suggestion. We added this sentence in the manuscript.

The initially planned study involved physical exercises with a maximum age for inclusion criteria of 60 years-old to limit the cardiovascular risks.

We modified the sentence as follows:

All subjects self-declared being physically active, healthy, non-smokers, with no known diseases and no pregnancy or lactation for women as well as living in France.

You are right. It would improve the quality of this work. The following sentences were added:

More specifically, from January 1st to May 11th (end of lockdown) there were 20 weeks. With 2 tests per week in average per participant, 40 tests were performed.

Heart rate variability:

Thank you for the information about the HRV measurement devices.

“The H7 is the most used RR-recording device, the TP5+ uses the exact same technology:

Comparison of Heart-Rate-Variability Recording With Smartphone

Photoplethysmography, Polar H7 Chest Strap, and Electrocardiography. Daniel J

Plews, Ben Scott, Marco Altini, Matt Wood, Andrew E Kilding, Paul B Laursen. Int J

Sports Physiol Perform. 2017 Nov 1;12(10):1324-1328. doi: 10.1123/ijspp.2016-

0668. DOI: 10.1123/ijspp.2016-0668.

The smartphone application is just a Bluetooth receiver, using the standard BLE

protocol, which does not interfere in any ways with the recording. It is just a wireless

system. The results would have been exactly the same if the RR intervals had been

stored on the smartphone memory and downloaded to a computer using a wire.

https://web.archive.org/web/20170130085524/https://www.bluetooth.com/specificatio

ns/bluetooth-core-specification”

We followed your recommendation and have incorporated this information in the manuscript as follows:

The H7 is the most used RR-recording device, the TP5+ uses the exact same technology [23]. The smartphone application is a Bluetooth receiver, using the standard BLE protocol, which does not interfere in any ways with the recording.

We added this information as follows:

The RR intervals from the orthostatic tests were first analyzed to remove ectopic beats from the recordings, the algorithms used are currently not available to the public.

Visual analogue scale:

We understand your concern but the question was on purpose very vague as we aimed to obtain a general feeling of the subject. We did not focus on a special component of the mood as vigor, anxiety or anger. Here we display a screenshot (in French) of the VAS to clarify this point.

Since it is a limitation of the present study, we added the following sentence in the manuscript:

Finally, the VAS allowed to only rate a “general well-being” but not any specific mood components as vigor, anxiety, anger etc. Therefore, it remains vague and incorporates probably different psychological states among participants.

Correlations:

As suggested, we moved this part to the “statistics” chapter.

We tested LF and HF only in absolute units. Since LF and HF are labelled nLF and nHF, we don’t believe that we should clarify in the manuscript.

Statistics Section

Again, your relevant comment helps us to improve the manuscript. The following sentence was added:

Regarding the group effect division adopted (WB- vs WB+), the criteria was a change in VAS >2, that corresponded to 20% change in the scale. Such a large change aimed to lower the intra-individual variability.

Adjustments made in the manuscript regarding the other possible group divisions are well done.

The statistical powers were calculated using the F-statistic values and the degrees of freedom, according to Scheffé, H. (1959), The Analysis of Variance. New York: John-Wiley. p. 227 ; and Zar, J.H. (1999), Biostatistical Analysis (2nd ed.). NJ: Prentice-Hall, Englewood Cliffs. pp. 195-196. Those references were added in the manuscript as well as a short explanation about the computations.

Statistical power SP is reported for each ANOVA performed, the computations take into account the F-statistic values (expected and observed) and the degrees of freedom [25,26].

Results

Although partially complete, the previous requests regarding results section were well done.

Please, present in the manuscript the HR and HRV mean values (and SD) of the sample, in each recording position per period (BLS, CFN, and RCV) and per group in each period.

For not being redundant with the figures 1 and 2, where the means (and SEM) are displayed, we politely disagree to report once more the values.

We added this information in the abstract and in the manuscript, as follows:

Moreover, RMSSD in standing position was correlated to VAS.

Please see our reply above re. the redundancy to report these values in figures and in manuscript.

The changes in parameters were analyzed using normalized values while the correlations were computed using absolute values. Sentences have been added in the Result section

All these changes are reported in normalized units.

All correlations were computed on absolute values.

Discussion

Thank you. Done.

Also, in the subsequent sentence, I suggest you adopt other expression instead of “performance”, it may sound out of context, since the paragraph is not talking about entrainment or performance specifically, but in part about physical activity, that is a broader concept.

You are right. We modified “performance” for “responses”.

Table 1 reports Pearson’s correlation coefficient (R), p value, and 95% confidence interval (CI) in the supine and standing positions for HR and HRV parameters against VAS.

Also, please, discuss the significant correlation between VAS and RMSSD observed in standing position.

As requested, we added the following sentence:

Most of these correlations were found when HRV was measured in supine position, except for RMSSD in standing position. This later result emphasizes the value of RMSSD as a key parameter of HRV analysis.

Limitations:

This section was really improved. Congratulations.

Thank you! We have added one more limitation on VAS

Please, change “is” to “was” in the following sentence of the limitations: “The separation criterion between the WB+ and WB- groups is arbitrary”.

Done

Conclusion

The adjustments made in conclusion were nice. Congratulations.

In my opinion, changing: ”general cardiovascular detraining” to “cardiovascular health” may provide to the reader a more assertive sentence. Feel free to incorporate or not that suggestion.

We agree and modified as suggested.

Done. Thank you!

Table 1:

Please report the measurement units of HR and HRV indexes in the first column of table 1.

Done.

Figures 1 and 2:

Figure legends describe the following symbols: “* p < 0.05 for difference with

BSL. # p < 0.05 for difference with CFN.”. However, in the figures 1 and 2 the symbols are one or two asterisks “*” or “(**)”. Please, clarify what the two asterisks symbol means.

We added the missing information.

* p < 0.05, ** p < 0.01 for difference with BSL

Attachment

Submitted filename: REV PLoS - 3.docx

Click here for additional data file.^{(38KB, docx)}

PLoS One. doi: 10.1371/journal.pone.0242303.r005

Decision Letter 2

Daniel Boullosa

2 Nov 2020

Effects of COVID-19 lockdown on heart rate variability

PONE-D-20-22573R2

Dear Dr. Bourdillon,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Daniel Boullosa

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

PLoS One. doi: 10.1371/journal.pone.0242303.r006

Acceptance letter

Daniel Boullosa

4 Nov 2020

PONE-D-20-22573R2

Effects of COVID-19 lockdown on heart rate variability

Dear Dr. Bourdillon:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

If we can help with anything else, please email us at plosone@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Daniel Boullosa

Academic Editor

PLOS ONE

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

S1 Data

(TXT)

Click here for additional data file.^{(65B, txt)}

Attachment

Submitted filename: Reviewer comments.docx

Click here for additional data file.^{(63.8KB, docx)}

Attachment

Submitted filename: REV PLoS - 3.docx

Click here for additional data file.^{(38KB, docx)}

Data Availability Statement

Data underlying the study is available on Zenodo (http://doi.org/10.5281/zenodo.4058116).

[pone.0242303.ref001] 1.Lemoine V, Delibéros M, Bessarion C, Champion S. Confinement: un impact certain sur l’activité physique, le temps passé assis et le temps passé devant un écran. Press Release. 2020. https://www.santepubliquefrance.fr/presse/2020/confinement-un-impact-certain-sur-l-activite-physique-le-temps-passe-assis-et-le-temps-passe-devant-un-ecran [Google Scholar]

[pone.0242303.ref002] 2.Brooks SK, Webster RK, Smith LE, Woodland L, Wessely S, Greenberg N, et al. The psychological impact of quarantine and how to reduce it: rapid review of the evidence. Lancet Lond Engl. 2020;395: 912–920. 10.1016/S0140-6736(20)30460-8 [DOI] [PMC free article] [PubMed] [Google Scholar]

[pone.0242303.ref003] 3.Wang C, Pan R, Wan X, Tan Y, Xu L, Ho CS, et al. Immediate Psychological Responses and Associated Factors during the Initial Stage of the 2019 Coronavirus Disease (COVID-19) Epidemic among the General Population in China. Int J Environ Res Public Health. 2020;17 10.3390/ijerph17051729 [DOI] [PMC free article] [PubMed] [Google Scholar]

[pone.0242303.ref004] 4.Martinez-Ferran M, de la Guía-Galipienso F, Sanchis-Gomar F, Pareja-Galeano H. Metabolic Impacts of Confinement during the COVID-19 Pandemic Due to Modified Diet and Physical Activity Habits. Nutrients. 2020;12 10.3390/nu12061549 [DOI] [PMC free article] [PubMed] [Google Scholar]

[pone.0242303.ref005] 5.Lavie CJ, Arena R, Swift DL, Johannsen NM, Sui X, Lee D-C, et al. Exercise and the cardiovascular system: clinical science and cardiovascular outcomes. Circ Res. 2015;117: 207–219. 10.1161/CIRCRESAHA.117.305205 [DOI] [PMC free article] [PubMed] [Google Scholar]

[pone.0242303.ref006] 6.Pareja-Galeano H, Sanchis-Gomar F, Lucia A. Physical activity and depression: type of exercise matters. JAMA Pediatr. 2015;169: 288–289. 10.1001/jamapediatrics.2014.3501 [DOI] [PubMed] [Google Scholar]

[pone.0242303.ref007] 7.Brown HE, Pearson N, Braithwaite RE, Brown WJ, Biddle SJH. Physical activity interventions and depression in children and adolescents: a systematic review and meta-analysis. Sports Med Auckl NZ. 2013;43: 195–206. 10.1007/s40279-012-0015-8 [DOI] [PubMed] [Google Scholar]

[pone.0242303.ref008] 8.Schmitt L, Regnard J, Parmentier AL, Mauny F, Mourot L, Coulmy N, et al. Typology of “Fatigue” by Heart Rate Variability Analysis in Elite Nordic-skiers. Int J Sports Med. 2015;36: 999–1007. 10.1055/s-0035-1548885 [DOI] [PubMed] [Google Scholar]

[pone.0242303.ref009] 9.Hynynen E, Konttinen N, Kinnunen U, Kyröläinen H, Rusko H. The incidence of stress symptoms and heart rate variability during sleep and orthostatic test. Eur J Appl Physiol. 2011;111: 733–741. 10.1007/s00421-010-1698-x [DOI] [PubMed] [Google Scholar]

[pone.0242303.ref010] 10.Thayer JF, Yamamoto SS, Brosschot JF. The relationship of autonomic imbalance, heart rate variability and cardiovascular disease risk factors. Int J Cardiol. 2010;141: 122–131. 10.1016/j.ijcard.2009.09.543 [DOI] [PubMed] [Google Scholar]

[pone.0242303.ref011] 11.Laborde S, Mosley E, Thayer JF. Heart Rate Variability and Cardiac Vagal Tone in Psychophysiological Research—Recommendations for Experiment Planning, Data Analysis, and Data Reporting. Front Psychol. 2017;8: 213 10.3389/fpsyg.2017.00213 [DOI] [PMC free article] [PubMed] [Google Scholar]

[pone.0242303.ref012] 12.Kim H-G, Cheon E-J, Bai D-S, Lee YH, Koo B-H. Stress and Heart Rate Variability: A Meta-Analysis and Review of the Literature. Psychiatry Investig. 2018;15: 235–245. 10.30773/pi.2017.08.17 [DOI] [PMC free article] [PubMed] [Google Scholar]

[pone.0242303.ref013] 13.Holzman JB, Bridgett DJ. Heart Rate Variability Indices as Bio-Markers of Top-Down Self-Regulatory Mechanisms: A Meta-Analytic Review. Neurosci Biobehav Rev. 2017. 10.1016/j.neubiorev.2016.12.032 [DOI] [PubMed] [Google Scholar]

[pone.0242303.ref014] 14.Goldberger JJ. Sympathovagal balance: how should we measure it? Am J Physiol. 1999;276: H1273–1280. 10.1152/ajpheart.1999.276.4.H1273 [DOI] [PubMed] [Google Scholar]

[pone.0242303.ref015] 15.Wang Y-P, Kuo TBJ, Li J-Y, Lai C-T, Yang CCH. The relationships between heart rate deceleration capacity and spectral indices of heart rate variability during different breathing frequencies. Eur J Appl Physiol. 2016;116: 1281–1287. 10.1007/s00421-016-3332-z [DOI] [PubMed] [Google Scholar]

[pone.0242303.ref016] 16.Medeiros AR, Michael S, Boullosa DA. Make it easier! Evaluation of the “vagal-sympathetic effect” in different conditions with R-R intervals monitoring. Eur J Appl Physiol. 2018;118: 1287–1288. 10.1007/s00421-018-3855-6 [DOI] [PubMed] [Google Scholar]

[pone.0242303.ref017] 17.Hayano J, Yuda E. Pitfalls of assessment of autonomic function by heart rate variability. J Physiol Anthropol. 2019;38: 3 10.1186/s40101-019-0193-2 [DOI] [PMC free article] [PubMed] [Google Scholar]

[pone.0242303.ref018] 18.Pomeranz B, Macaulay RJ, Caudill MA, Kutz I, Adam D, Gordon D, et al. Assessment of autonomic function in humans by heart rate spectral analysis. Am J Physiol. 1985;248: H151–153. 10.1152/ajpheart.1985.248.1.H151 [DOI] [PubMed] [Google Scholar]

[pone.0242303.ref019] 19.Force Task. Heart rate variability. Standards of measurement, physiological interpretation, and clinical use. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Eur Heart J. 1996;17: 354–381. [PubMed] [Google Scholar]

[pone.0242303.ref020] 20.Dixon EM, Kamath MV, McCartney N, Fallen EL. Neural regulation of heart rate variability in endurance athletes and sedentary controls. Cardiovasc Res. 1992;26: 713–719. 10.1093/cvr/26.7.713 [DOI] [PubMed] [Google Scholar]

[pone.0242303.ref021] 21.Buchheit M. Monitoring training status with HR measures: do all roads lead to Rome? Front Physiol. 2014;5: 73 10.3389/fphys.2014.00073 [DOI] [PMC free article] [PubMed] [Google Scholar]

[pone.0242303.ref022] 22.Bourdillon N, Schmitt L, Yazdani S, Vesin J, Millet GP. Minimal Window Duration for Accurate HRV Recording in Athletes. Front Neurosci. 2017;11: 456 10.3389/fnins.2017.00456 [DOI] [PMC free article] [PubMed] [Google Scholar]

[pone.0242303.ref023] 23.Plews DJ, Scott B, Altini M, Wood M, Kilding AE, Laursen PB. Comparison of Heart-Rate-Variability Recording With Smartphone Photoplethysmography, Polar H7 Chest Strap, and Electrocardiography. Int J Sports Physiol Perform. 2017;12: 1324–1328. 10.1123/ijspp.2016-0668 [DOI] [PubMed] [Google Scholar]

[pone.0242303.ref024] 24.Thorpe RT, Strudwick AJ, Buchheit M, Atkinson G, Drust B, Gregson W. Tracking Morning Fatigue Status Across In-Season Training Weeks in Elite Soccer Players. Int J Sports Physiol Perform. 2016;11: 947–952. 10.1123/ijspp.2015-0490 [DOI] [PubMed] [Google Scholar]

[pone.0242303.ref025] 25.Zar JH. Biostatistical Analysis (2nd ed.). Prentice-Hall,. Prentice-Hall,. NJ: Englewood Cliffs; 1999. pp. 195–196. [Google Scholar]

[pone.0242303.ref026] 26.Scheffé H. The Analysis of Variance. The Analysis of Variance. New-York: John-Wiley; 1959. p. 227. [Google Scholar]

[pone.0242303.ref027] 27.Matias T, Dominski FH, Marks DF. Human needs in COVID-19 isolation. J Health Psychol. 2020;25: 871–882. 10.1177/1359105320925149 [DOI] [PubMed] [Google Scholar]

[pone.0242303.ref028] 28.Jiménez-Pavón D, Carbonell-Baeza A, Lavie CJ. Physical exercise as therapy to fight against the mental and physical consequences of COVID-19 quarantine: Special focus in older people. Prog Cardiovasc Dis. 2020. 10.1016/j.pcad.2020.03.009 [DOI] [PMC free article] [PubMed] [Google Scholar]

[pone.0242303.ref029] 29.Parouty J, Al Haddad H, Quod M, Leprêtre PM, Ahmaidi S, Buchheit M. Effect of cold water immersion on 100-m sprint performance in well-trained swimmers. Eur J Appl Physiol. 2010;109: 483–490. 10.1007/s00421-010-1381-2 [DOI] [PubMed] [Google Scholar]

[pone.0242303.ref030] 30.Hug B, Heyer L, Naef N, Buchheit M, Wehrlin JP, Millet GP. Tapering for marathon and cardiac autonomic function. Int J Sports Med. 2014;35: 676–683. 10.1055/s-0033-1361184 [DOI] [PubMed] [Google Scholar]

[pone.0242303.ref031] 31.Hnatkova K, Šišáková M, Smetana P, Toman O, Huster KM, Novotný T, et al. Sex differences in heart rate responses to postural provocations. Int J Cardiol. 2019;297: 126–134. 10.1016/j.ijcard.2019.09.044 [DOI] [PMC free article] [PubMed] [Google Scholar]

PERMALINK

Effects of COVID-19 lockdown on heart rate variability

Nicolas Bourdillon

Sasan Yazdani

Laurent Schmitt

Grégoire P Millet

Roles

Abstract

Introduction

Methods

Results

Conclusion

Introduction

Methods

Experimental design

Participants

Heart rate variability

Visual analogic scale (VAS)

Statistics

Results

Fig 1. HR, RMSSD, LF and HF before (BSL), during (CFN) and after (RCV) the strict lockdown period in France in 76 participants who deteriorated or maintained their well-being over the CFN period.

Fig 2. HR, RMSSD, LF and HF before (BSL), during (CFN) and after (RCV) the strict lockdown period in France in 19 participants who improved their well-being over the CFN period.

Table 1. Pearson’s correlation coefficient (R), p value, and 95% confidence interval (CI) in the supine and standing positions for HR and HRV parameters against VAS.

Discussion

Limitations

Conclusion

Supporting information

Data Availability

Funding Statement

References

Decision Letter 0

Daniel Boullosa

Roles

Author response to Decision Letter 0

Decision Letter 1

Daniel Boullosa

Roles

Author response to Decision Letter 1

Decision Letter 2

Daniel Boullosa

Roles

Acceptance letter

Daniel Boullosa

Roles

Associated Data

Supplementary Materials

Data Availability Statement

ACTIONS

PERMALINK

RESOURCES

Similar articles

Cited by other articles

Links to NCBI Databases