Training load, sports performance, physical and mental health during the COVID-19 pandemic: A prospective cohort of Swiss elite athletes

Yannis Karrer; Stefan Fröhlich; Samuel Iff; Jörg Spörri; Johannes Scherr; Erich Seifritz; Boris B Quednow; Malte Christian Claussen

doi:10.1371/journal.pone.0278203

. 2022 Dec 1;17(12):e0278203. doi: 10.1371/journal.pone.0278203

Training load, sports performance, physical and mental health during the COVID-19 pandemic: A prospective cohort of Swiss elite athletes

Yannis Karrer ^1,^*, Stefan Fröhlich ^2,³, Samuel Iff ¹, Jörg Spörri ^2,³, Johannes Scherr ², Erich Seifritz ¹, Boris B Quednow ⁴, Malte Christian Claussen ^1,⁵

Editor: Tauqeer Hussain Mallhi⁶

PMCID: PMC9714901 PMID: 36454814

Abstract

Background

The COVID-19 pandemic and associated restrictions have led to abrupt changes in the lives of elite athletes.

Objectives

The objective of this prospective cohort study was to examine training load, subjective sports performance, physical and mental health among Swiss elite athletes during a 6-month follow-up period starting with the first Swiss lockdown.

Methods

Swiss elite athletes (n = 203) participated in a repeated online survey evaluating health, training, and performance related metrics. After the first assessment during the first lockdown between April and May 2020, there were monthly follow-ups over 6 months.

Results

Out of 203 athletes completing the first survey during the first lockdown, 73 athletes (36%) completed all assessments during the entire 6-month follow-up period. Sports performance and training load decreased during the first lockdown and increased again at the beginning of the second lockdown in October 2020, while symptoms of depression and financial fears showed only a transient increase during the first lockdown. Self-reported injuries and illnesses did not change significantly at any timepoint in the study. Stricter COVID-19 restrictions, as measured by the Government Stringency Index (GSI), were associated with reduced subjective sports performance, as well as lower training intensity, increased financial fears, poorer coping with restrictions, and more depressive symptoms, as measured by the 9-item module of the Patient Health Questionnaire-9 (PHQ-9).

Conclusion

This study revealed a negative impact of the COVID-19 restrictions on sports performance, training load and mental health among Swiss elite athletes, while the rate of self-reported injuries and illnesses remained unaffected.

Introduction

The COVID-19 pandemic can be considered as one of the major challenges of our time. It led to numerous COVID-19 deaths and associated restrictions may have contributed to an increased loss of livelihoods. Moreover, the COVID-19 pandemic and associated government restrictions were concomitant with a growing mental health crisis in Europe [1, 2].

Mental health symptoms and disorders such as depression, anxiety, and sleeping disorders are common among elite athletes [3]. The COVID-19 pandemic has led to abrupt changes in the training routine and social support network that may be critical components for mental health problem coping in elite athletes [4, 5]. In addition, elite athletes may have been confronted with social isolation, postponement or cancellation of competitions, limited training possibilities, lack of meaning in daily activity, and fears concerning the continuation of an athletic career [6]. Therefore, elite athletes may represent a subpopulation especially challenged by the psychiatric burden of the COVID-19 pandemic [7].

Mental health impairments are capable of impairing performance, increasing the risk of musculoskeletal injuries, and prolonging the recovery from physical injuries [3]. Therefore, mental health is obviously strongly linked to physical health and sports performance.

The International Olympic Committee (IOC) consensus statement 2019 on mental health in elite athletes defines elite athletes as those athletes that compete at professional, Olympic or collegiate levels [3]. A recent systematic review found negative effects of the COVID-19 pandemic on overall physical fitness, training load, negative emotions and sleep quality among elite athletes [8]. However, elite athletes may be more resilient to the stressors of the COVID-19 pandemic compared with non-athletes [9] and novice athletes [10].

In Switzerland, the strictness of government restrictions [11] as well as the specific restrictions in professional sports varied substantially over time; professional sports were only allowed during the second lockdown [12, 13]. Therefore, a longitudinal study design over a longer period of time after the lockdown ended (including the beginning of the second lockdown) may add valuable information about the effects of the ongoing COVID-19 pandemic and associated restrictions.

Accordingly, the primary objective of this study was to examine sports performance among Swiss elite athlete during a 6-month follow-up starting at the beginning of the COVID-19 pandemic (first wave in Switzerland) and following until the beginning of the 2^nd lockdown. Secondary objectives were the evaluation of mental health, physical health, training, and potential explanatory factors. We hypothesized that the lockdown has a negative impact on sports performance, mental health, physical health training and load among elite athletes, which is reversed upon lifting of the lockdown.

Materials and methods

Study design

This prospective cohort study was designed as a monthly 6-months follow-up during the COVID-19 pandemic in elite athletes. Participants entered their data online in an online questionnaire (REDCap 9.10.0 - © 2020 Vanderbilt University) [14]. The link to the follow-up questionnaires were each sent by email to the participants one month after the last survey was completed. If there was no response, a reminder email was sent 7 days after. The local ethics committee reviewed this study and judged it not to fall under the scope of the Swiss Human Research Act (HRA) by means of a declaration of non-responsibility (KEK-ZH-NR: Req-2020-00408). The data of this study were analysed anonymously, therefore no consent (written or oral) is needed.

Study setting

For a detailed timeline of the study, refer to Fig 1. The first lockdown included the closure of sport facilities, public places, businesses, the restriction of contacts, the prohibition of any event, competition, or team training and asking the people to stay at home. These comprehensive actions resulted in the exposure of all participants to the “first lockdown”. As part of the step-by-step reduction of restrictions, the closure of sport facilities ended on the 10^th May 2020; team training was allowed again from 11^th May 2020 [12].

The second lockdown included restrictions such as the restriction of contacts, the closure of public places, businesses as well as sport facilities on the 22^nd of December 2020 [13]. In contrast to the first lockdown, professional athletes were still allowed to train in compliance with certain conditions and restrictions. There was no coherent definition of professional sports by the Swiss Government. As an objective measure to quantify the strictness of government policies regarding COVID-19 restrictions the government stringency index (GSI) was used [11]. The complete 6-month and partly the 5-month follow-up surveys were carried out during the 2^nd lockdown which did not end within the 6-month follow-up period (FUP).

Participants

A sample of adult elite athletes was recruited during the 25^th of April 2020 and 25^th of May 2020, of which baseline data were collected. An online questionnaire was distributed to elite level athletes of various sports via their respective sports clubs or national sports federation. In this study the same definition of elite athletes was used as defined in the 2019 IOC consensus statement on mental health in elite athletes [3]. A minimum training volume of 1 hour per day before the COVID-19 pandemic, a minimum age of 18 years and language skills in French or German were required to be included as a participant. Exclusion criteria were incomplete data, the participation in a non-Olympic sport or a sport that is not recognized by the IOC. The participants of this study did not receive any compensation for their participation.

Demographic and sports variables

The collected variables consisted of gender, age, sports type, training volume in hours, subjective intensity, subjective athletic performance, existence of a secondary occupation inclusive workload during the lockdown, and then monthly until 6^th month of follow-up. To evaluate status before lockdown, participants were asked to estimate following factors in the last month before the pandemic from memory: subjective performance (0–100% of subjective maximum performance), training volume (hours/day), training intensity (0–100% of subjective maximum intensity), financial fears were assessed by the question “Did you have financial fears?” and answered by a visual analogue scale (VAS) ranging from 0–100 (0 meaning “none”; 100 meaning “extreme”), alcohol (days/month) respectively cannabis consumption (days/month).

Additionally, the participants were asked if their income from sports is sufficient for their livelihood and independent of additional income (yes/no). Participants were also asked about own confirmed COVID-19 infections (yes/no). The subjective coping with the restrictions was assessed by the question “I am getting along well with the restrictions to limit the COVID-19 pandemic?” which was evaluated by VAS ranging from 0–100 (0 meaning “does not apply”; 100 meaning “does apply”). Worries for their sporting career was assessed by the question “Are your worrying about the continuation of your sporting career because of the COVID-19 pandemic?” which was evaluated by VAS ranging from 0–100 (0 meaning “no worries”; 100 meaning “extreme worries”). All questions about the demographic and sports variables were part of the survey during lockdown and all monthly surveys of the FUP.

Clinical questionnaires

The validated German version of the short form (10 items) of the Spielberger State-Trait Anxiety Inventory (STAI) was used to obtain the anxiety rating [15]. The questionnaire investigates two types of anxiety: the state anxiety as a measure for the reaction to current events and the trait anxiety which represents hardly changeable personal characteristics. The 9-item module of the Patient Health Questionnaire (PHQ-9) as a reliable and valid tool was used to screen the participants for depressive symptoms [16]. As a validated tool to evaluate sleep disorder symptoms, the Insomnia Severity Index (ISI) was used to identify symptoms of actual sleep disturbances [17, 18]. The extracts from the Pittsburgh Sleep Quality Index served to obtain precise parameters of sleep (i.e. sleep latency, sleep duration) [19]. The Oslo Sports Trauma Research Center (OSTRC) questionnaire was used to assess current and already existing health problems like illness or injury [20–22]. All mentioned clinical questionnaires were part of the survey during lockdown and all monthly surveys of the FUP.

Statistical methods

Parametric data was expressed as mean ± standard deviation (SD) and frequency tables for categorical data. Comparisons of demographic data between time points test was used for categorical tables with more than four fields, one-way analysis of variance for continuous variables, and Kruskal-Wallis rank test for variables nonmetric variables. Statistical significance was set at p <0.05. For sports performance, we fitted a general least squares random-effects model using the score of the time point as the dependent variable, pre-lockdown performance as the independent variable and gender, team sports, injury, activity, GSI, occupation percentage as covariates. To adjust for psychiatric measures, we added the results of PHQ-9, ISI, STAI, financial fears and worries for their sporting career. All explanatory variables that had an association with the independent variables at p<0.20 in the univariable analyses were included in the multivariable-adjusted analyses. Using a stepwise backward elimination process, the least significant variables were then removed from the base model. Only variables with p<0.05 remained in the final parsimonious model. Stata Statistical Software (Release 13, College Station, TX) was used to analyse the data.

Patient and public involvement

There was no involvement of the public or the participants in the design, recruitment, conduct, choice of outcome measures, reporting or dissemination of this study. Participants that reported suicidal thoughts or at least moderate depressive symptoms were contacted by the study team; personal contact details were provided, and professional help was offered.

Results

Participants

During the first lockdown, 203 athletes completed the survey and were included in the analysis. Seventy-three (36%) athletes finalised the study, while 130 (64%) athletes were lost due to unknown reasons. The largest drop-out (37%) was seen between the first survey during the 1^st lockdown and second survey 1-month after the 1^st lockdown. After the initial drop-out, the monthly drop-out rate decreased until the end of the observation period and ranged between 3–18%. Descriptive data and characteristics of participating athletes at the first lockdown and the 6-month FUP are shown in Table 1. The age of participants ranged between 18–54 years (only two participants were >37 years old) at the first survey during lockdown and 18–37 years at all follow-up surveys. Overall, the age of participants, the ratio between male and female participants and the sufficiency of income did not change significantly over the observation period (at p<0.05).

Table 1. Summary table of demographic data at different time points.

	Lockdown	1-month FUP	2-month FUP	3-month FUP	4-month FUP	5-month FUP	6-month FUP
	N = 203	N = 127	N = 107	N = 88	N = 80	N = 75	N = 73
Age at Survey Date	24.1 (± 5.3) years	24.3 (± 5.0) years	23.9 (± 4.6) years	23.7 (± 4.5) years	23.8 (± 4.5) years	24.0 (± 4.4) years	23.7 (± 4.5) years
Female	45%	50%	53%	47%	48%	51%	48%
Summer Sports	52%	43%	38%	36%	34%	41%	38%
Winter Sports	48%	57%	62%	64%	66%)	59%	62%
Working	60%	59%	61%	61%	59%	63%	62%
Workload	67.1 (± 8.2) %	66.0 (± 29.2) %	64.8 (± 28.0) %	65.0 (± 27.9) %	61.7 (± 28.0) %	65.6 (± 28.1) %	64.0 (± 28.6) %
Sufficient income	53%	54%	50%	49%	54%	52%	52%

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FUP: follow-up period.

Primary analysis

Sports performance

The subjective sports performance was significantly lower during the first lockdown and at the 1-month and 6-month follow-up compared to before the lockdown (Fig 2A). For the multivariable regression analysis of sports performance see Table 2.

Fig 2 — (A) subjective performance (%); (B) training volume (h/d); (C) subjective training intensity (%); (D) financial fears (VAS 0–100); (E) worries for sporting career (VAS 0–100); (F) coping with restrictions (VAS 0–100). The dotted lines represent the 95% CI interval of the “before” measurement.

Table 2. Multivariable and univariable regression analysis of subjective sports performance, financial fears, STATE sum and PHQ-9 sum.

Subjective performance (primary analysis)			State anxiety (STATE) sum (secondary analysis)
	Univariable	Multivariable		Univariable	Multivariable
Self-reported injury/illness	-8.284^***	-7.337^***	Patient Health Questionnaire-9 (PHQ-9) sum	2.067^***	1.393^***
Patient Health Questionnaire-9 (PHQ-9) sum	-1.853^***	-1.512^***	Trait anxiety sum (TRAIT)	0.705^***	0.405^***
Government Stringency Index (GSI)	-0.258^***	-0.210^***	Insomnia Severity Sum Index (ISI) sum	0.902^***	0.320^***
Subjective performance before (%)	0.218^***	0.183^**	Age at survey date	0.078	0.157^*
Insomnia Severity Sum Index (ISI) sum	-0.635^***	ns	Financial fears	0.094^***	0.031^*
State anxiety (STATE) sum	-0.325^***	ns	Training volume (h/d)	-0.822^***	ns
Trait anxiety (TRAIT) sum	-0.267^**	ns	Coping with restrictions	-0.065^***	ns
Financial fears	-0.099^**	ns	Subjective training intensity (%)	-0.048^***	ns
			Government Stringency Index (GSI)	0.048^*	ns
R² within = 0.1100, between = 0.2475, overall = 0.1627; Prob > χ² = 0.0000			R² within = 0.2504, between = 0.7116, overall = 0.5958; Prob > χ² = 0.0000
Financial fears (secondary analysis)			Patient Health Questionnaire-9 (PHQ-9) sum (secondary analysis)
	Univariable	Multivariable		Univariable	Multivariable
Occupation (vs. not)	-11.774^***	-6.452^**	Insomnia Severity Sum Index (ISI) sum	0.300^***	0.164^***
Team sport (vs. individual)	-9.833^**	-4.803^*	State anxiety (STATE) sum	0.165^***	0.101^***
Patient Health Questionnaire-9 (PHQ-9) sum	1.761^***	0.959^**	Trait anxiety (TRAIT) sum	0.185^***	0.077^***
Financial fears before	0.753^***	0.642^***	Subjective performance (%)	-0.033^***	-0.016^***
State anxiety (STATE) sum	0.488^***	0.218^*	Coping with restrictions	-0.026^***	-0.010^**
Government Stringency Index (GSI)	0.150^**	0.121^**	Government Stringency Index (GSI)	0.025^***	0.011^*
Trait anxiety (TRAIT) sum	0.601^***	ns	Financial fears	0.027^***	0.009^*
Subjective performance (%)	-0.134^***	ns	Occupation (vs. not)	1.013^*	ns
Subjective training intensity (%)	-0.107^***	ns	Training volume (h/d)	-0.329^***	ns
Coping with restrictions	-0.106^**	ns	Subjective training intensity (%)	-0.022^***	ns
R² within = 0.0624, between = 0.5971, overall = 0.4080; Prob > χ² = 0.0000			R² within = 0.3329, between = 0.6680, overall = 0.6063; Prob > χ² = 0.0000

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* p < 0.05

** p < 0.01

*** p < 0.001; ns: non-significant

Secondary analysis

Physical health and changes in training volume and intensity

At p<0.05, self-reported injury and illness did not change significantly over at any time point during this study. After the significant decrease of the training volume during the lockdown, training volume increased back to pre-lockdown levels (Fig 2B). An additional insignificant decrease (at p<0.05) in training volume was seen at the 6-month follow-up. Multivariable regression analysis (R² within = 0.0232, between = 0.04523, overall = 0.3003; Prob > χ² = 0.0000) showed that the training volume was moderately positively associated with the training volume before the lockdown (B = 0.269, p<0.001), strongly positively associated with winter sport (vs. summer sport) (B = 0.499, p<0.001), and strongly negatively associated with occupation (B = -0.728, p<0.001), weakly negatively associated with age at survey date (B = -0.027, p<0.05) and the PHQ-9 sum (B = -0.077, p<0.001).

The subjective training intensity was significantly decreased during the lockdown and at the 1-month follow-up compared to pre-lockdown levels and decreased again significantly at the 6-month follow-up (Fig 2C). Multivariable regression analysis (R² within = 0.0953, between = 0.2114, overall = 0.1527; Prob > χ² = 0.0000) revealed the training intensity to be weakly positively associated with training intensity before the lockdown (B = 0.225, p<0.001), weakly negatively associated with age at survey date (B = -0.601, p<0.01), strongly negatively associated with self-reported injury/illness (B = -5.219, p<0.01) and the Government Stringency Index (B = -0.311, p<0.001) and moderately negatively associated with the PHQ-9 sum (B = -1.374, p<0.001).

Financial fears and worries about their sporting career

After the significant increase of financial fears during the first lockdown compared to pre-lockdown levels, financial fears decreased and but increased again at the 6-month FUP (Fig 2D). At p<0.05, there was no significant difference between the financial fears during any time point of the FUP compared with before the lockdown, although financial fears were higher at every time point of the FUP. For the multivariable regression analysis of financial fears, see Table 2. The worries for their sporting career did not change significantly at any time point during this study (Fig 2E).

Coping with government restrictions

The subjective ability to cope with restrictions increased significantly during the first 3 month of the FUP but decreased again to lockdown baseline values (Fig 2F). At the end of the 6-month FUP, the ability to cope was even lower than during the first lockdown but did not reach statistical significance at p<0.05. Multivariable regression analysis (R² within = 0.0627, between = 0.2324, overall = 0.1213; Prob > χ² = 0.0000) indicated that subjective coping with restrictions has a strong negative association with the PHQ-9 sum (B = -1.364, p<0.001) and a weak negative association with the GSI (B = -0.166, p<0.001) and worries for sporting career (B = -0.136, p<0.001).

The state anxiety (STATE) sum decreased significantly after the lockdown at the 2-month and 3-month time point before it increased again to baseline values of the lockdown (Fig 3A). For the multivariable regression analysis of the state anxiety sum, see Table 2. The trait anxiety (TRAIT) sum did not change significantly at any time point during this study (Fig 3B). With 4.5 (±3.1) points, the averaged PHQ-9 sum was highest during the first lockdown, interpreted as minimal symptoms of depression. There was a significant decrease at the 2-month and 3-month time point of the FUP compared to during the first lockdown, followed by a mild and insignificant increase of the PHQ-9 sum (Fig 3C). For the multivariable regression analysis of the PHQ-9 sum see Table 2. Neither the insomnia severity index (ISI) sum nor the total sleeping time (h) did change significantly at any time point of this study (Fig 3D and 3E).

Fig 3 — (A) state anxiety sum; (B) trait anxiety sum; (C) Patient Health Questionnaire-9 (PHQ-9) sum; (D) Insomnia Severity Index (ISI) sum; (E) total sleeping time (h/d); (F) alcohol drinking (d/month). The dotted lines represent the 95% confidence intervals of the first measurement of the variable, either during lockdown or from memory before lockdown.

Alcohol and cannabis consumption

Only two participants reported the consumption of cannabis of which the consumption frequency did not change at any time point during this study. Before the lockdown and in all follow-up surveys alcohol consumption was significantly lower than during the lockdown (Fig 3F). About half (range: 35–57%) of all participants reported not drinking any alcohol at each time point of this study.

COVID-19 infections

During the first lockdown until the 4-month survey of the FUP 1–2% of participants, respectively 4% at the 5-month and 9% at the 6-month survey reported own confirmed COVID-19 infections.

Discussion

Among elite athletes, the negative effects on subjective sports performance, training load, symptoms of depression, financial fears, and alcohol consumption during the first lockdown returned back to pre-lockdown levels estimated from memory after the lockdown ended. At the beginning of the 2^nd lockdown the same factors changed, but only the reduction in sports performance and training intensity reached significance at p<0.05.

Our results regarding the period around the first lockdown seem to be in line with several previous studies that found reduced (objective) sports performance [23], reduced training load [24–28], negative impact on general mental state [24, 29, 30], increased negative emotions [25, 27, 31–33], increased risk of adjustment disorder [34] during lockdown among elite athletes. However, one study found increased sleeping time [28] and several previous studies found increased symptoms of insomnia during lockdown among elite athletes [25, 27, 28, 32, 33], which we both did not find in our study. We also did not find any gender specific increases in insomnia (or any other measures) like two previous studies [25, 33]. There was also a systematic review that found negative effect of the COVID-19 pandemic on overall physical fitness, training load, negative emotions and sleep quality among elite athletes [8]. In comparison to our study, that review did not include the beginning of a second lockdown and only examined the effects at the beginning of the pandemic.

Regarding the post-lockdown period, a study among elite rugby players did also find decreased depressive symptoms after the lockdown ended, but with no changes in symptoms of anxiety [35]. Because there was no comparison to pre-lockdown levels, it can only be speculated if symptoms of depression returned to pre-lockdown levels and if there was no effect on anxiety like in our study. Similar to our results, a prospective cohort study among Iranian elite athletes found decreased training load, positive mood and life satisfaction during lockdown compared to reopening phase and the following semi-lockdown [24]. They also found strongly increased economic damage (from 10.3% during lockdown in March 2020 to 52.3% in the reopening phase in May 2020 respectively 56.3% during the semi lockdown condition in July 2020) compared with pre-lockdown levels [24]. In contrast to our study, where training load returned to pre-lockdown levels, they found strongly decreased training load during all phases (-88% during lockdown, -85% during reopening, -86% during semi-lockdown) [24]. In Switzerland there were considerably stricter restrictions (as measured by the GSI) during the first lockdown [11]. Additionally, Iranian elite athletes only received privileges to exercise during the reopening phase [24]. In contrast, Swiss elite athletes received funds and the privileges to exercise shortly after the first lockdown ended [36], which likely reduced the negative impact of the COVID-19 restrictions on training load, financial fears. Although it is reasonable to think that financial fears and economic damage may correlate, we cannot exclude possible economic damage in Swiss elite athletes respectively changes in financial fears in Iranian elite athletes as they were not examined.

Our findings revealed a low number of participants that reported symptoms corresponding to moderate or moderately-to-severe depression, which was also found in one study among elite rugby players [35] but not in another study among professional football (i.e., soccer) players during the first lockdown [37]. Compared with rates of depression among elite athletes provided by the literature ranging from 4% [38] to 68% [39], the prevalence of increased PHQ-9 values in our cohort tends to the lower end of the range with 1–8% over the entire period of our study. In accordance with previous studies [9, 10], our study seems to support the hypothesis that a higher level of competition (i.e., elite level) may provide a protective effect on mental health and sports performance during the COVID-19 pandemic.

Although the reduced training load during the first lockdown may have offered an opportunity to cure existing injuries or illnesses, there were no significant changes in self-reported injuries or illnesses at any timepoint. One study also found no changes of the incidence of injuries among professional football (soccer) players comparing pre- with post-lockdown [40], whereas two other studies found lower injury rates in the 2020/21 season compared with normal seasons before the pandemic [41, 42]. In our study, self-reported injuries and illnesses were unsurprisingly associated with lower subjective sports performance and lower training intensity. It can be assumed that sports performance and training intensity decrease in the presence of an injury or illness.

The investigation of potential explanatory factors for observed changes revealed several associations: stricter COVID-19 government restrictions reflected by a higher GSI were associated with lower subjective sports performance and training intensity, more depressive symptoms, increased financial fears and worse coping with restrictions. However, our study cannot answer if those associations reflect causation or correlation. More depressive symptoms measured by the PHQ-9 were found to be associated with worse subjective sports performance and coping with restrictions as well as more symptoms of anxiety (STATE, TRAIT), sleeping problems (ISI sum) and financial fears. Those findings seem plausible because mental health symptoms and athletic performance cannot be separated and anxiety and sleep problems are common symptoms of depression [3]. Besides an association of winter sports and training volume, no association between winter and summer sports with any tested parameter was found. The positive association between winter sports and training volume may be explained by the postponement of many competitions in summer sports. Also, the privileges to train again fell largely into the follow-up period that corresponds to the preparation for the winter sports season. Swiss elite athletes received funds and the privileges to exercise shortly after the first lockdown ended [36], which likely reduced the negative impact of the COVID-19 restrictions on sports performance, training and mental health.

Methodological considerations

There are a couple of limitations one should consider when interpreting the study findings: first, as only questionnaires were used, the results therefore remain a subjective report of sports performance, training load and symptoms of mental and physical health. Clinical examination would be required for an accurate assessment of mental and physical health. Second, a certain degree of selection or reporting bias cannot be ruled out because mental health symptoms may increase or decrease the ability or willingness to participate. Third, the participants of this study represent a national cohort that was exposed to certain circumstances specific to elite athletes in Switzerland which may differ to other countries. Fourth, considering the collective of elite athletes representing only a small fraction of all athletes, the number of participants in this study was relatively large. The drop-out rate of about two thirds of participants over the 6-month FUP can be considered as high, however, not unusual for a follow-up study using online questionnaires only. However, drop-out participants were not significantly different from the participants that stayed in the study. Because we included every participant at any time point in the multivariable regression analysis, the effect of the high drop-out rate may be limited. We speculate that the main reasons for this high drop-out rate may be the losing of interest to participate because of the COVID-19 topic itself, the detailed survey or the relatively long FUP. Fifth, as with every questionnaire-based study we cannot rule out a potential recall bias. Sixth, the GSI only represents the restrictions overall and does not put extra weight on sport-specific restrictions [11] and the changes over time may have influenced the participants with unknown latency.

Conclusion

This study revealed that the negative impacts of the COVID-19 pandemic and associated restrictions on the subjective sports performance, training load and mental health in Swiss elite athletes returned to pre-lockdown levels after the first lockdown ended, while no effects on self-reported injuries and illnesses were observed. A similar negative effect on training load and sports performance was also observed after the beginning of the 2^nd lockdown, but again with no changes of self-reported injuries and illnesses. Future research should also address if the observed effects on sports performance, training load, physical health, and mental health in the post-lockdown respectively the beginning of the second lockdown period also have occurred in other countries under similar or different conditions.

Supporting information

S1 Checklist. STROBE (Strengthening The Reporting of OBservational Studies in Epidemiology) checklist.

(PDF)

Click here for additional data file.^{(499.4KB, pdf)}

Acknowledgments

The participation of all the athletes was greatly appreciated.

Data Availability

All data files are available from Zenodo at https://doi.org/10.5281/zenodo.5655745.

Funding Statement

The authors received no specific funding for this work.

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PLoS One. doi: 10.1371/journal.pone.0278203.r001

Decision Letter 0

Tauqeer Hussain Mallhi

21 Jul 2022

PONE-D-21-35814Sports performance, mental health, physical health, and training load during the progression of the COVID-19 pandemic: A cohort study of Swiss elite athletesPLOS ONE

Dear Dr. Claussen,

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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: Yes

Reviewer #3: Yes

Reviewer #4: Partly

Reviewer #5: Yes

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

Reviewer #1: I Don't Know

Reviewer #2: Yes

Reviewer #3: Yes

Reviewer #4: Yes

Reviewer #5: Yes

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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: Yes

Reviewer #3: Yes

Reviewer #4: Yes

Reviewer #5: Yes

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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

Reviewer #3: Yes

Reviewer #4: Yes

Reviewer #5: Yes

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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: This study is well written with good methodological concept. Especially, the limitations section was well articulated.

I have some minor suggestions mentioned below-

1) Definition of elite athlete?

2) Line 82: "designed as a 6-month follow-up during the COVID-19 pandemic". Here, it should be highlighted that, this study actually did monthly follow up for 6 month.

3) Total number of participants should be mentioned at participants section

4) Dropout rate is very high, which is a major problem in this study. Though it was addressed and clarified in the limitations section, there is chance for further proper explanation regarding how the study is yet valid with this limitation. Hope, this will increase further the acceptance of this study.

5) Analysis part seemed to be authentic, but it is suggested for further comments from an expert reviewer

6) Line 273: Our findings revealed a low number of participants that reported symptoms indicating moderate to moderately-to-severe depression--- How it indicates depression level?

7) It would be better if conclusion section contains some new things or suggestion based on the study findings.

Reviewer #2: GENERAL COMMENTS

In this manuscript, the authors evaluated the relationship between COVID-19 pandemic and mental/physical health among the elite athletes. It was interesting that the value changed depending on the timing and the factors. However, the authors should clarify the definition of elite athlete in this study. Are they national team member? Although the authors revealed the differences of the prevalence between this study and other studies, it is difficult to evaluate about this.

Major

・P11 Line184-185, Figure 2a: Description about this part is insufficient. In this figure, there does not seem to have significant difference compared to before the lockdown. The authors need to show statistical numbers more specifically. And the authors need to show the meaning of dotted lines in the Fig. 2.

・P13 Line 201: How do you think about there is a difference between winter and summer sports?

・P15 Line 246: Suddenly the description about COVID-19 has begun. Please describe how to diagnose or assess the COVID-19 in the method.

Minor

P5 Line 109: The authors need to explain the abbreviation for FUP here

P14 Line 217-245: The authors need to indicate where these descriptions are related to the figure.

Reviewer #3: Is the scientific merit of the study high enough to justify publication?

Hypothesis:

No specific hypothesis is stated.

Purpose:

The objective of this prospective cohort study was to examine subjective sports performance, mental and physical health, training load among Swiss elite athlete during a 6-month follow-up period starting with the first Swiss lockdown in response to the COVID-19 pandemic.

Methods:

Swiss elite athletes (n=203) participated in a repeated online survey evaluating mental and physical health factors, as well as training and performance related metrics. After the first assessment during the first lockdown between April and May 2020, there were monthly follow-ups over a 6-month period as the pandemic progressed.

Are the methods appropriate for investigating the hypothesis?

There was no hypothesis specifically stated. Therefore, the methods do not look to investigate a particular hypothesis. However, the methods support the aim of the study.

Are the methods appropriate for investigating the stated goals?

Ideally they are. However, with only 36% of the initial cohort finishing the study, the effectiveness of the methodology (repeated online survey) must be evaluated.

Do the results support the hypothesis?

As no hypothesis was stated, the results cannot refute/accept a hypothesis.

Do the results support the purpose(s)?

No. With an appropriate response rate the findings of this paper could be evaluated vis-à-vis the remainder of the publications on the topic of the effect of COVID and its lockdowns on the mental and physical health of elite athletes. However, as this is grossly under-represented, the ability to draw conclusions based on the results in questionable.

Limitations:

1) Only questionnaires used, no clinical examinations

2) Possible selection bias of the limited number of respondents

3) Only Swiss elite athletes included

4) Only 36% of players completed the full study

5) Different sports may have had different restrictions, potentially greater than those mandated by the state lockdowns

Does the study make a large enough contribution to the existing literature to justify publication?

It does not right now. There have been a number of papers on the same basic topic with the same result which have a higher academic veracity due to adequate responses and/or clinical data. There is little in this paper which would affect my decision-making or standard of care.

Is the study suitable for publication in PLOS ONE?

No, for reasons stated above.

Reviewer #4: Dear Authors,

Kindly address the following questions and make the amendments accordingly:

1. Why there are two (2) titles? Suggest to change the title to “Training load, sports performance, physical and mental health during the COVID-19 pandemic: A prospective cohort of Swiss elite athletes.

2. The abstract’s format is wrong: supposed to be written in one paragraph and begin with the introduction or background of the study.

3. In sentence 30, grammatical error: …… among Swiss elite “athletes”……

4. In sentence 38, suggest to change to “Out of 203 athletes…….”

5. In sentence 53, …… can be considered as one of the major challenges……

6. In sentence 58, there were too many references (3 – 6) for a well-known short fact, suggest to limit to 1 or 2 reference(s).

7. In sentence 62, again, too many references were cited (7 – 11) for such a short sentence, suggest to limit to 1 or 2 reference(s).

8. In sentence 69, grammatical mistake: and an increased “in”……

9. The whole introduction only focused on the literature reviews of the negative impact and contributing factors of mental health in elite athletes, how about the effect of the COVID-19 pandemic on physical health, training load and sports performance among elite athletes from other studies?

10. In sentence 84, the link to the follow-up questionnaires was sent “by” email…….

11. The local ethics committee judged the study did not fall under the scope of the Swiss Human Research Act, so is there any ethical approval by any institutional review board or independent ethics committee before conducting the study? Do the participants of the study give written consent?

12. In sentence 90, refer to “Figure 1”.

13. In sentences 94 and 95, kindly standardize in writing the date: 10th May 2020; 11th May 2020

14. In sentence 97, kindly standardize in using a capital letter, i.e. “lockdown” instead of Lockdown

15. In sentences 99 – 102, why there was variation in terms of duration of follow-up from 2nd follow-up onward, unlike monthly follow-up as you have mentioned? Also, why is the word “GSI” appear at the end of the sentence 102?

16. In sentence 105, …… professional sports were still allowed to train in compliance with……

17. In sentence 109, replace FUP with follow-up.

18. In sentence 111, a sample of adult elite athletes “aged between ? and ?” was recruited from 25th April 2020 till 25th May 2020…….

19. In sentence 113, ......via their respective sports club or national sports federation.

20. Kindly revise and be more specific in the inclusion criteria: “a minimum training volume of 1 hour per day before the COVID-19 pandemic”. For example, if an elite athlete only trained for ½ hour one day before the lockdown, do you recruit this athlete?

21. Why do you exclude elite athletes from non-IOC-recognized sports? Are they non considered elite athletes even if they are representing the country to compete and participate in international championship? (selection bias)

22. How do you calculate your sample size? What is the sampling method?

23. In sentence 124, 0 – 100% of subjective “measurement”, not maximum

24. In sentence 125, existential fears were assessed as only having financial fear, is this reliable and validated? Please cite the reference that you used in assessing the existential fears.

25. In sentence 127, (……100 meaning “extreme fear”), alcohol (days/ month) and cannabis (days/ month) consumption. Why you did not include cigarette smoking?

26. In sentence 132, ……which was evaluated by VAS……

27. In sentence 133, worries for their "sporting" career……

28. In sentence 137, the FUP abbreviation supposes to be mentioned earlier before using it in the sentence 109.

29. In sentences 153 and 154, ……and Kruskal-Wallis test is non-parametric test for not normally distributed variables.

30. In sentence 162, Stata Statistical Software (Release 13, College Station, TX).

31. In sentence 177, what do you mean by “the rate of occupation”, aren’t all the elite athletes working as full-time athletes?

32. For tablet 1, suggest to divide into Male and Female for each column (each follow-up period)

33. In sentence 185, remove the word “mark”, and spell “Figure” in a complete word

34. In sentence 195, remove the word “mark” (please do proper proofreading)

35. In sentence 235, grammatical mistake: time point

36. The discussion can be improved and written clearer. For example, the initial paragraphs mainly discussed own findings/ results, and only the last two paragraphs compared with other studies/ literature.

37. In sentence 289, is it selection bias or reporting bias?

38. Can this study represent all the elite national athletes as there was selection bias in terms of sports from the beginning? Kindly address this as one of the limitations, and also mention another limitation is recall bias in a questionnaire-based study.

39. Do you attempt to improve the retention and reduce the dropout rate since you already foresee a high degree of dropout for a questionnaire-based study? Kindly discuss how can you improve the retention?

Thank you for your cooperation.

Reviewer #5: In the submitted paper the authors investigate the subjective sports

performance, mental and physical health, training load among Swiss elite athlete during a 6-month

follow-up period starting with the first Swiss lockdown in response to the COVID-19 pandemic in a prospective cohort study.

The study revealed a negative impact of the COVID-19 restrictions on sports performance,

training load and mental health among Swiss elite athletes, while the rate of self-reported injuries and illnesses remained unaffected.

Methods and statistics of the study are adequate and state of the art.

However, the results of this study are not surprising and are in line with other studies analyzing the impact of Lock Downs in the general public. Moreover, the paper is descriptive and I am missing some recommendations for future look downs. Also it is specific to the swiss situation which was a quite mild lockdown situation compared to other countries, . So, it may be interesting to compare these data sets with data sets from other countries with more stringent lockdowns. So, all in all data which can be published but the question is whether the significance of the data I such high to justify that it is published in Plos one.

**********

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Reviewer #1: Yes: Dr. Panchanan Acharjee

Reviewer #2: No

Reviewer #3: No

Reviewer #4: Yes: Alston Choong

Reviewer #5: No

**********

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PLoS One. 2022 Dec 1;17(12):e0278203. doi: 10.1371/journal.pone.0278203.r002

Author response to Decision Letter 0

20 Sep 2022

Reviewer #1: This study is well written with good methodological concept. Especially, the limitations section was well articulated.

Thank you very much!

I have some minor suggestions mentioned below-

Ad 1) Definition of elite athlete?

We used the same definition of elite athletes as defined in the IOC consensus statement on mental health in elite athletes (Reardon CL, Hainline B, Aron CM, et al. Br J Sports Med 2019;53:667–699.).

To prevent misconceptions we added this definition in the Introduction “The International Olympic Committee (IOC) consensus statement 2019 on mental health in elite athletes defines elite athletes as those athletes that compete at professional, Olympic or collegiate levels (3).” and clarified that this definition was used in our study in the Methods: “In this study the same definition of elite athletes was used as defined in the 2019 IOC consensus statement on mental health in elite athletes (3).”

Ad 2) Line 82: "designed as a 6-month follow-up during the COVID-19 pandemic". Here, it should be highlighted that, this study actually did monthly follow up for 6 month.

Thank you, we corrected this sentence.

Ad 3) Total number of participants should be mentioned at participants section

We strictly adhere to the rule to report numbers in the results section, not in the methods section (see STROBE guidelines). Total number of participants is described in the first paragraph of the results.

Ad 4) Dropout rate is very high, which is a major problem in this study. Though it was addressed and clarified in the limitations section, there is chance for further proper explanation regarding how the study is yet valid with this limitation. Hope, this will increase further the acceptance of this study.

Despite best efforts to keep the respondent number high during follow up, the 6th month follow-up included only roughly 1/3 of the original participants. This is inherent in the longitudinal design of the study. We reported all dropout rates accordingly. Despite selective follow-up participation, there was minimal indication of selection bias, data were non-significant among participants, dropouts, and the entire cohort. Hence, we think that the overall conclusion remains valid from this cohort.

Ad 5) Analysis part seemed to be authentic, but it is suggested for further comments from an expert reviewer

We leave this decision at the discretion of the editor.

Ad 6) Line 273: Our findings revealed a low number of participants that reported symptoms indicating moderate to moderately-to-severe depression--- How it indicates depression level?

Thank you for your comment. We changed the wording to “corresponding to”.

The PHQ-9 as an instrument to detect depression symptoms has been validated in elite athletes (Gouttebarge V, et al. International Olympic Committee (IOC) Sport Mental Health Assessment Tool 1 (SMHAT-1) and Sport Mental Health Recognition Tool 1 (SMHRT-1): towards better support of athletes' mental health. Br J Sports Med. 2021 Jan;55(1):30-37. doi: 10.1136/bjsports-2020-102411. Epub 2020 Sep 18. PMID: 32948518; PMCID: PMC7788187).

Following cut-offs are widely used: ≥5=mild, ≥10=moderate, ≥15=moderately severe and ≥20=severe (Manea, L.; Gilbody, S.; McMillan, D. Optimal cut-off score for diagnosing depression with the Patient Health Questionnaire (PHQ-9): A meta-analysis. Can. Med. Assoc. J. 2012, 184, E191–E196).

Ad 7) It would be better if conclusion section contains some new things or suggestion based on the study findings.

We added following suggestion for future research: “Future research should also address if the observed effects on sports performance, training load, physical health, and mental health in the post-lockdown respectively the beginning of the second lockdown period also have occurred in other countries under similar or different conditions.”

Reviewer #2: In this manuscript, the authors evaluated the relationship between COVID-19 pandemic and mental/physical health among the elite athletes. It was interesting that the value changed depending on the timing and the factors. However, the authors should clarify the definition of elite athlete in this study. Are they national team member? Although the authors revealed the differences of the prevalence between this study and other studies, it is difficult to evaluate about this.

Major

The dotted lines represent the 95% CI interval of the “before” measurement, so that readers can spot differences from the baseline more easily. So, subfigures A, B, C , D and F were significantly different from baseline values. We are happy to provide a table with the results in the supplementary material, however we think the current graph allows readers to grasp the development over time more easily.

・P13 Line 201: How do you think about there is a difference between winter and summer sports?

Thank you for this input. We added a brief discussion about the potential explanations: “The positive association between winter sports and training volume may be explained by the postponement of many competitions in summer sports. Also, the privileges to train again fell largely into the follow-up period that corresponds to the preparation for the winter sports season.”

・P15 Line 246: Suddenly the description about COVID-19 has begun. Please describe how to diagnose or assess the COVID-19 in the method.

The participants were asked about own confirmed COVID-19 infections (yes/no question). COVID-19 infections are usually confirmed by rt-PCR. We added following sentence to the methods section “Participants were also asked about own confirmed COVID-19 infections (yes/no).”

Minor

P5 Line 109: The authors need to explain the abbreviation for FUP here

Thank you, we explained the abbreviation in the mentioned sentence.

P14 Line 217-245: The authors need to indicate where these descriptions are related to the figure.

We added the related figures where they were missing in the results.

Reviewer #3: Is the scientific merit of the study high enough to justify publication?

Hypothesis:

No specific hypothesis is stated.

Our hypothesis was that the lockdown has a negative impact on sports performance, mental health, physical health training and load among elite athletes, which is reversed upon lifting of the lockdown.

For clarification we added following sentence in the introduction: “We hypothesized that the lockdown has a negative impact on sports performance, mental health, physical health training and load among elite athletes, which is reversed upon lifting of the lockdown.”

Purpose:

Methods:

Are the methods appropriate for investigating the hypothesis?

There was no hypothesis specifically stated. Therefore, the methods do not look to investigate a particular hypothesis. However, the methods support the aim of the study.

Are the methods appropriate for investigating the stated goals?

Ideally they are. However, with only 36% of the initial cohort finishing the study, the effectiveness of the methodology (repeated online survey) must be evaluated.

Drop-out participants were not significantly different from the participants that stayed in the follow-up. Therefore, we added following sentence to the limitations: “However, drop-out participants were not significantly different from the participants that stayed in the study.”

“Because we included every participant at any time point in the multivariable regression analysis, the effect of the high drop-out rate may be limited.”

Do the results support the hypothesis?

As no hypothesis was stated, the results cannot refute/accept a hypothesis.

Do the results support the purpose(s)?

Because it is always important to consider all relevant limitations when drawing conclusions from any study, we addressed all relevant limitations (including the drop-out rate). Drop-out participants were not significantly different from the participants that stayed in the follow-up. We therefore think that the ability to draw conclusions based on the results of our study is there.

Limitations:

1) Only questionnaires used, no clinical examinations

2) Possible selection bias of the limited number of respondents

3) Only Swiss elite athletes included

4) Only 36% of players completed the full study

5) Different sports may have had different restrictions, potentially greater than those mandated by the state lockdowns

Ad 1) Questionnaires were all validated and are used in clinical context. We are unsure which clinical examinations would have added to the primary objective of sports performance among Swiss elite athletes. We understand that individual tests per athlete could have given a more detailed information about performance, but those tests are specific for the sport and cannot be compared with each other.

Ad 2) This limitation is discussed in the limitation section. We are aware that there can be a selection bias. However, we still think that the results add to the literature in a meaningful way.

Ad3) Correct.

Ad 4) Correct. However, the data was missing at random, and we have no indication that the results are biased by those loss to follow up.

Ad 5) The different effects on the different sports were taken into account by evaluation of the training time and intensity.

Does the study make a large enough contribution to the existing literature to justify publication?

Is the study suitable for publication in PLOS ONE?

No, for reasons stated above.

Thank you for your comments.

We want to highlight that we submitted this manuscript almost 1 year ago in November 2021 and waited since then for the completion of the review process respectively a first decision. Since several studies were published during this waiting period, we performed an updated literature search. We included the relevant publications that we found by the updated literature search in our revised manuscript.

Although there have been a number of papers on the same basic topic, we could not find any other prospective cohort study that examined the beginning of a second lockdown and/or studies that observed participants over a similar or longer period of time after the second lockdown ended. We also could not find any prospective cohort study that examined sports performance, training load, physical and mental health among elite athletes including all of the following time periods: pre- lockdown (1st lockdown), during lockdown (1st lockdown), post lockdown (first lockdown), beginning of the second lockdown. We therefore think that our study adds to the body of evidence in a meaningful way that justifies a publication in PLOS ONE.

We also think that it is valuable to have data from different countries with different situations regarding restrictions, funds/privileges to exercise for elite athletes. With more studies from different countries, patterns may emerge that may affect future decision-making of physicians as well as politicians and standard care.

Reviewer #4: Dear Authors,

Kindly address the following questions and make the amendments accordingly:

Thank you for this valuable input. We changed the title and removed the second subtitle.

2. The abstract’s format is wrong: supposed to be written in one paragraph and begin with the introduction or background of the study.

We corrected the format and added a study background part.

3. In sentence 30, grammatical error: …… among Swiss elite “athletes”……

Corrected.

4. In sentence 38, suggest to change to “Out of 203 athletes…….”

Corrected.

5. In sentence 53, …… can be considered as one of the major challenges……

Corrected.

6. In sentence 58, there were too many references (3 – 6) for a well-known short fact, suggest to limit to 1 or 2 reference(s).

We limited the references to one reference as suggested.

7. In sentence 62, again, too many references were cited (7 – 11) for such a short sentence, suggest to limit to 1 or 2 reference(s).

We limited the references to two references as suggested.

8. In sentence 69, grammatical mistake: and an increased “in”……

Corrected.

Thank you for this valuable input.

We complemented the introduction and discussion with up-to-date literature on mental health as well as training load, physical health and sports performance.

10. In sentence 84, the link to the follow-up questionnaires was sent “by” email…….

Corrected.

The local Ethics Committee is an independent ethics committee. Therefore, no additional ethical approval is necessary according to Swiss Law. The data of this study were analysed anonymously, therefore no consent (written or oral) is needed.

12. In sentence 90, refer to “Figure 1”.

According to our understanding of the PLOS ONE Manuscript Body Formatting Guidelines (https://journals.plos.org/plosone/s/submission-guidelines#loc-figures-and-tables), abbreviations like “Fig” oder “Figs” should be used instead of Figure/Figures.

13. In sentences 94 and 95, kindly standardize in writing the date: 10th May 2020; 11th May 2020

Corrected.

14. In sentence 97, kindly standardize in using a capital letter, i.e. “lockdown” instead of Lockdown

Corrected.

The variation in terms of duration of follow-up are explained by individually different dates of the first survey completion. The first survey during lockdown was completed between 25th April until 26th May 2020. If a participant completed the first survey on 1st May 2020, he would receive the 1-month follow-up survey by mail on 29th May 2020 (1 month after the first survey). Depending on how fast the participant responded to each survey, the timeframes may vary a bit.

As a part of figure 1, the GSI (“government stringency index”) appears in the legend of figure 1 to cite the source.

16. In sentence 105, …… professional sports were still allowed to train in compliance with……

Changed to “[…] professional athletes were still allowed to train in compliance with […]”.

17. In sentence 109, replace FUP with follow-up.

Changed to “follow-up period”.

18. In sentence 111, a sample of adult elite athletes “aged between ? and ?” was recruited from 25th April 2020 till 25th May 2020…….

We added the report of age ranges at each survey in the “Participants” section of the results: “The age of participants ranged between 18-54 years (only two participants were 37 years old) at the first survey during lockdown and 18-37 years at all follow-up surveys.”

19. In sentence 113, ......via their respective sports club or national sports federation.

Corrected.

If an athlete only trained ½ hour per day before the pandemic, he would be excluded according to our inclusion criteria.

We changed the wording from “the participation in a non-Olympic sport or a sport that is not recognized by the IOC.” to “a sport that is not recognized by the IOC.” as there was no athlete that competes in a IOC recognized but non-Olympic sport and we aimed to examine elite athletes competing in IOC recognized sports.

22. How do you calculate your sample size? What is the sampling method?

There was no sample size calculation possible as no such event like a pandemic lockdown was ever present before and we couldn’t estimate the magnitude of the effect on the outcome variable. So, we used a convenience sample in this study.

23. In sentence 124, 0 – 100% of subjective “measurement”, not maximum

0-100% subjective maximum refers to “0-100% of subjective maximum performance” respectively “0-100% of subjective maximum intensity”.

24. In sentence 125, existential fears were assessed as only having financial fear, is this reliable and validated? Please cite the reference that you used in assessing the existential fears.

It is correct that we aimed to examine existential fears in the sense of financial fears but explicitly asked for financial fears. To prevent misconceptions or accidentally using invalid methods, we changed existential fears to financial fears in the whole paper.

25. In sentence 127, (……100 meaning “extreme fear”), alcohol (days/ month) and cannabis (days/ month) consumption. Why you did not include cigarette smoking?

We agree that tobacco or nicotine containing products (such as cigarettes) could have also been asked in the survey. We did not include smoking, because from our clinical experience elite athletes may indeed use tobacco (in particular in the form of spit tobacco/snus) or other nicotine containing products, but rarely smoke cigarettes. On the other hand, alcohol and cannabis consumption in elite athletes has been reported relatively often. Additionally, we speculate that the potential risk of recall bias may be higher when asking about the monthly use of tobacco/nicotine containing products compared to alcohol and cannabis because tobacco/nicotine containing products are more often consumed multiple times daily.

26. In sentence 132, ……which was evaluated by VAS……

Corrected.

27. In sentence 133, worries for their "sporting" career……

Corrected.

28. In sentence 137, the FUP abbreviation supposes to be mentioned earlier before using it in the sentence 109.

Corrected.

29. In sentences 153 and 154, ……and Kruskal-Wallis test is non-parametric test for not normally distributed variables.

That’s right. In case a non-normal distributed variable was present, for non-parametric variables, this test was used to analyse the data.

30. In sentence 162, Stata Statistical Software (Release 13, College Station, TX).

Changed.

31. In sentence 177, what do you mean by “the rate of occupation”, aren’t all the elite athletes working as full-time athletes?

Not all elite athletes have sufficient income from sports for their livelihood and therefore have an additional occupation. See table 1 for percentages of athletes with sufficient income from sports for each timepoint.

To clarify and prevent misconceptions, we changed the sentence 177 from “the rate of occupation and the sufficiency of income did not change significantly over the observation period (at p0.05).” to “the sufficiency of income did not change significantly over the observation period (at p0.05).”

32. For tablet 1, suggest to divide into Male and Female for each column (each follow-up period)

There were no significant differences by gender in any of the evaluated variables, hence we did not analyse the genders separately.

33. In sentence 185, remove the word “mark”, and spell “Figure” in a complete word

We removed every “mark” in the manuscript.

34. In sentence 195, remove the word “mark” (please do proper proofreading)

We removed every “mark” in the manuscript.

35. In sentence 235, grammatical mistake: time point

Changed.

Thank you for this valuable input.

37. In sentence 289, is it selection bias or reporting bias?

Both biases cannot be ruled out. Therefore, we added “or reporting bias”.

38. Can this study represent all the elite national athletes as there was selection bias in terms of sports from the beginning?

They way of recruiting did not ensure a representative sample of all elite national athletes. However, drop-out participants were not significantly different from the participants that stayed in the follow-up. Therefore, we added following sentence to the limitations “However, drop-out participants were not significantly different from the participants that stayed in the study.” Potential selection bias is already addressed in the limitations section.

Kindly address this as one of the limitations, and also mention another limitation is recall bias in a questionnaire-based study.

We also added this limitation in the limitations section: “Fifth, as with every questionnaire-based study we cannot rule out a potential recall bias.”

We attempted to improve retention by a reminder mail. If the participants did not respond to the questionnaire sent by email, they received a reminder email 7 days after (see section “Study Design” 5-6th line). Our study was designed on short term notice as soon as the lockdown was foreseeable, and the study protocol did not foresee any additional measures to improve retention.

Thank you for your cooperation.

Thank you for your valuable inputs!

Reviewer #5: In the submitted paper the authors investigate the subjective sports performance, mental and physical health, training load among Swiss elite athlete during a 6-month follow-up period starting with the first Swiss lockdown in response to the COVID-19 pandemic in a prospective cohort study.

The study revealed a negative impact of the COVID-19 restrictions on sports performance, training load and mental health among Swiss elite athletes, while the rate of self-reported injuries and illnesses remained unaffected.

Methods and statistics of the study are adequate and state of the art.

However, the results of this study are not surprising and are in line with other studies analysing the impact of Lock Downs in the general public. Moreover, the paper is descriptive and I am missing some recommendations for future look downs. Also it is specific to the swiss situation which was a quite mild lockdown situation compared to other countries, . So, it may be interesting to compare these data sets with data sets from other countries with more stringent lockdowns. So, all in all data which can be published but the question is whether the significance of the data I such high to justify that it is published in Plos one.

Thank you very much for your time and valuable input.

Most but not all of our results are in line with other studies examining the first lockdown among elite athletes. However, to not publish studies that are not surprising or contradicting existing evidence leads to publication bias which we aim to prevent.

Because there has never been a comparable situation, it is important to monitor and describe the effects of such an extraordinary situation on several variables among elite athletes over time.

We speculated that for example receiving funds and privileges to exercise may have reduced the impact of the COVID-19 restrictions on sports performance, training, and mental health. However, our study cannot answer if there was a causal relationship which would justify to make clear recommendations regarding COVID-19 related restrictions regarding elite athletes.

As you stated correctly, our study is specific to the Swiss situation which you have considered as a quite mild lockdown situation comparing to other countries. The valuation of a “mild” lockdown is highly depending on the compared country. As an example: Switzerland had a GSI (as an objective measure to quantify the strictness of government policies regarding the COVID-19 restrictions) of about 73/100 vs. China with about 81/100 vs. Iran with about 59/100 during the first lockdown. Because the restrictions varied so much between countries/regions and over time, we think that our study provides valuable data for future comparisons with longitudinal data of other countries with similar or different restrictions. Even though we also think it would be interesting to compare our data with data sets of other countries, such a comparison was out of the scope of our study.

Although, there have been a number of papers on the same basic topic, we could not find any other prospective cohort study in elite athletes on the same topic that examined the beginning of a second lockdown and/or studies that observed participants over a similar or longer period of time after the second lockdown ended. We also could not find any prospective cohort study that examined sports performance, training load, physical and mental health among elite athletes including all of the following time periods: pre- lockdown (1st lockdown), during lockdown (1st lockdown), post lockdown (first lockdown), beginning of the second lockdown. We therefore think that our study adds to the body of evidence in a meaningful way that justifies a publication in PLOS ONE.

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PLoS One. doi: 10.1371/journal.pone.0278203.r003

Decision Letter 1

Tauqeer Hussain Mallhi

14 Nov 2022

Training load, sports performance, physical and mental health during the COVID-19 pandemic: A prospective cohort of Swiss elite athletes

PONE-D-21-35814R1

Dear Dr. Karrer,

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,

Tauqeer Hussain Mallhi, Ph.D

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Thank you for revising the manuscript.

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 #2: All comments have been addressed

Reviewer #4: All comments have been addressed

**********

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

Reviewer #2: Yes

Reviewer #4: Yes

**********

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

Reviewer #2: Yes

Reviewer #4: Yes

**********

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

Reviewer #2: Yes

Reviewer #4: Yes

**********

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

Reviewer #2: Yes

Reviewer #4: Yes

**********

6. Review Comments to the Author

Reviewer #2: (No Response)

Reviewer #4: Well done to the authors as all my queries have been explained and addressed well. Although the research topic is not something novelty as there were already many publications with the similar topic, however the outcomes and results from a Swiss elite athletes (can be considered as a niche population) may be able to provide some additional information especially when the number of COVID-19 infection cases are still fluctuating with the latest emergent of Omicron subvariant XBB and BQ1. Thus, more original studies will be able to provide insights, suggestions, recommendations and served as a references to develop more up-to-date, state-of-art guideline in case there is a further lockdown due to another wave of COVID-19 subvariant pandemic or any other infectious disease pandemic.

**********

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Reviewer #2: No

Reviewer #4: Yes: Alston Choong

**********

quillbot-extension-portal/quillbot-extension-portal

PLoS One. doi: 10.1371/journal.pone.0278203.r004

Acceptance letter

Tauqeer Hussain Mallhi

21 Nov 2022

PONE-D-21-35814R1

Training load, sports performance, physical and mental health during the COVID-19 pandemic: A prospective cohort of Swiss elite athletes

Dear Dr. Karrer:

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,

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on behalf of

Dr. Tauqeer Hussain Mallhi

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 Checklist. STROBE (Strengthening The Reporting of OBservational Studies in Epidemiology) checklist.

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Data Availability Statement

All data files are available from Zenodo at https://doi.org/10.5281/zenodo.5655745.

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PERMALINK

Training load, sports performance, physical and mental health during the COVID-19 pandemic: A prospective cohort of Swiss elite athletes

Yannis Karrer

Stefan Fröhlich

Samuel Iff

Jörg Spörri

Johannes Scherr

Erich Seifritz

Boris B Quednow

Malte Christian Claussen

Roles

Abstract

Background

Objectives

Methods

Results

Conclusion

Introduction

Materials and methods

Study design

Study setting

Fig 1. Study timeline.

Participants

Demographic and sports variables

Clinical questionnaires

Statistical methods

Patient and public involvement

Results

Participants

Table 1. Summary table of demographic data at different time points.

Primary analysis

Sports performance

Fig 2. Sports performance, training load, worries, fears, and coping.

Table 2. Multivariable and univariable regression analysis of subjective sports performance, financial fears, STATE sum and PHQ-9 sum.

Secondary analysis

Physical health and changes in training volume and intensity

Financial fears and worries about their sporting career

Coping with government restrictions

Fig 3. Symptoms of anxiety, depression, sleep disturbances and alcohol consumption.

Alcohol and cannabis consumption

COVID-19 infections

Discussion

Methodological considerations

Conclusion

Supporting information

Acknowledgments

Data Availability

Funding Statement

References

Decision Letter 0

Tauqeer Hussain Mallhi

Roles

Author response to Decision Letter 0

Decision Letter 1

Tauqeer Hussain Mallhi

Roles

Acceptance letter

Tauqeer Hussain Mallhi

Roles

Associated Data

Supplementary Materials

Data Availability Statement

ACTIONS

PERMALINK

RESOURCES

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