Evidence-based vs. social media based high-intensity interval training protocols: Physiological and perceptual responses

Katie L Hesketh; Hannah Church; Florence Kinnafick; Sam O Shepherd; Anton J M Wagenmakers; Matthew Cocks; Juliette A Strauss

doi:10.1371/journal.pone.0257685

. 2021 Sep 29;16(9):e0257685. doi: 10.1371/journal.pone.0257685

Evidence-based vs. social media based high-intensity interval training protocols: Physiological and perceptual responses

Katie L Hesketh ¹, Hannah Church ¹, Florence Kinnafick ², Sam O Shepherd ¹, Anton J M Wagenmakers ¹, Matthew Cocks ^1,^*, Juliette A Strauss ¹

Editor: Matthew M Schubert³

PMCID: PMC8480907 PMID: 34587217

Abstract

Objective

High intensity interval training (HIIT) is a time-efficient exercise modality to improve cardiorespiratory fitness, and has recently been popularised by social media influencers. However, little is known regarding acute physiological and perceptual responses to these online protocols compared to HIIT protocols used within research. The aim was to investigate acute physiological, perceptual and motivational responses to two HIIT protocols popular on social media, and compare these to two evidence-based protocols.

Methods

Twenty-seven recreationally active (>1 exercise session /week) participants (Age: 22±3y, BMI: 24.3±2.4) completed a randomised cross-over study, whereby each participant completed four HIIT protocols, two already established in research (Ergo-60:60 (cycling 10x60s at 100%W_maxwith 60s rest), BW-60:60 (body-weight exercises 10x60swith 60s rest)) and two promoted on social media (SM-20:10 (body-weight exercises 20x20swith 10s rest) and SM-40:20 (body-weight exercises 15x40s with 20s rest)). Blood lactate, heart rate (HR), feeling scale (FS), felt arousal scale (FSA), enjoyment and perceived competence were measured in response to each protocol.

Results

Significant differences were observed between BW-60:60 and SM-20:10 for the proportion of intervals meeting the ACSM high-intensity exercise criterion (>80% of HR_max) (BW-60:60 93±10%, SM-20:10 74±20%, P = 0.039) and change in lactate (BW-60:60 +7.8±3.7mmol/L, SM-20:10 +5.5±2.6mmol/L, P = 0.001). The percentage of time spent above the criterion HR was also significantly lower in SM-20:10 compared to all other protocols (Ergo-60:60 13.9±4.9min, BW-60:60 13.5±3.5min, SM-40:20 12.1±2.4min, SM-20:10 7.7±3.1, P<0.05). No differences were observed in lowest reported FS between protocols (P = 0.268), but FS decreased linearly throughout Ergo-60:60 and BW-60:60 (first vs. last interval P<0.05), but not in SM-20:10 or SM-40:20 (P>0.05). Enjoyment was higher upon completion of BW-60:60 compared to Ergo-60:60 and SM-40:20 (P<0.05).

Conclusions

This study shows that HIIT protocols available on social media offer an interesting real-world alternative for promoting exercise participation. Future studies should continue to investigate these highly popular and practical HIIT protocols.

Introduction

High intensity interval training includes brief, intermittent bursts of vigorous activity (typically between 80–100% HR_max), interspersed by periods of rest or recovery [1]. It is well established that HIIT is an effective time efficient means of training, resulting in equal or superior physiological adaptations to traditional moderate-intensity continuous training (MICT), despite substantially lower training volumes [2]. Following the positive reporting of this research through established media outlets, HIIT topped the American College of Sports Medicine’s (ACSM) Worldwide Fitness Trends list for the first time in 2014, and has remained in the top three since; returning to first place in 2018 [3–5]. In addition to the promotion of HIIT through the established media, its popularity has grown through endorsements by social media ‘influencers’ and the availability of fitness videos on media sharing sites. For example, one of the most popular HIIT exercise videos available on YouTube has over 15 million views. These social media influencers provide interesting opportunities to engage with audiences on a personal level, and can assist in the delivery of health improvement interventions [6]. Even though social media outlets have helped to establish HIIT as a popular training mode, there is no research comparing the protocols used in social media videos to those employed within the research. Although, one study has compared the acute responses to a video on a popular smartphone application (The 7-minute Workout (12x30s with 10s recovery)) with the same protocol carried out on a cycle ergometer, reporting greater mean and peak VO₂, heart rate (HR) and rate of perceived exertion following the cycling modality [7]. Importantly, the protocols promoted by social media influencers often employ interval durations and/or work-to-rest ratios that have not been backed by published research. Furthermore, within the peer-reviewed scientific research HIIT has primarily been developed as a time-efficient protocol to increase cardiorespiratory fitness. As such the exercise modalities used have been mainly aerobic in nature (e.g. running, cycling or body weight exercises using jumps) with the aim of eliciting a HR ≥80%HR_max. In contrast, protocols used within social media HIIT often include resistance-based exercises (e.g. press ups).

Recent work has suggested that the acute physiological response to HIIT may influence its long-term effectiveness. Importantly, Fiorenza et al. [8] demonstrated that metabolic stress is a key mediator of the acute molecular response to HIIT in endurance trained cyclists [8]. In mice, Hoshino et al. [9] suggested that repeated lactate accumulation during HIIT may be associated with training-induced mitochondrial adaptation. Furthermore Moholdt et al. [10], demonstrated that the mean HR achieved during HIIT intervals is central to long term increases in VO_2peak achieved following training, in patients with coronary heart disease. Taken together this data suggests that adaptation to long-term exercise training could be dependent on the magnitude of the stimulus received during each acute bout of exercise.

Although acute physiological responses are an important determinant of long-term adaptation, perceptual responses (positive/negative affect) during exercise and factors related to motivation (enjoyment and perceived competence) during and following exercise also influence the long term effectiveness of a training programme, as these factors can predict exercise adherence [10]. As such, assessing the acute psychological responses (i.e. how one is feeling during a HIIT session (affect)) to different high intensity interval exercise (HIIT) protocols may provide important information regarding future effectiveness. It has been hypothesised that the strenuous nature of HIIT may be a barrier to participation, as individuals are likely to avoid exercise if it is found to be aversive [11]. This assumption is based upon Dual Mode Theory proposed by Ekkekakis [12], which argues pleasure (affect) experienced during exercise declines when individuals exercise above ventilatory threshold. Therefore, assessing the affective response (feelings of pleasure/ displeasure) to HIIT protocols is important, as negative affect during exercise can act as a deterrent [13], while pleasurable experience is a determinant of exercise participation [14]. However, the majority of work used to support Dual Mode Theory has been carried out using continuous high intensity exercise, and its use within HIIT has been critiqued previously [15]. Motivation is well known to be a determinant of physical activity participation, a macro-theory of motivation which has been used to explain physical activity behaviour is Self Determination Theory [16]. Self Determination Theory proposes that motivation arises from the satisfaction of basic psychological needs (autonomy, competence and relatedness) [17]. It is the satisfaction of these basic psychological needs that have been shown to predict regular exercise participation [18]. As such, if individuals do not possess perceptions of competence during a HIIT protocol, they are more likely to disengage and not adhere to a programme. Finally, Stork and Martin Ginis [19] hypothesised that enjoyment predicts attitudes towards HIIT, which in turn mediate future intentions to participate.

Therefore, the aim of this study was to investigate the acute physiological, perceptual and motivational responses to two HIIT protocols popular on social media (SM-20:10, SM-40:20), and compare these to two evidence based HIIT protocols.

Methods

Participants

Twenty-seven recreationally active (defined as completing >1 but <4 structured exercise sessions per week) participants (male/female: n = 13/14, age: 22±3y, height: 1.70±0.09m, weight: 70.4±11.2kg, BMI: 24.3±2.4, VO_2peak: 42.2±7.2 ml.min^-1.kg^-1) were recruited from Liverpool John Moores University via internal email and posters. Exclusion criteria were those with a known cardiovascular or metabolic disease, pregnant or breastfeeding women, and those currently carrying an injury. The study was approved by the Liverpool John Moores Research Ethics Committee, and all participants gave written informed consent to the protocol which conformed to the Declaration of Helsinki.

Study design

The study used a randomized, counter-balanced crossover design to investigate the four HIIT protocols. Participants attended an initial experimental visit followed by 4 experimental trials to assess the acute physiological and psychological responses to the HIIT protocols. All visits were performed within the same laboratory environment at a similar time of day (between 11am and 3pm). All participants were asked to maintain their regular diet, to refrain from vigorous exercise 24 hours before each session and not to eat 3 hours before. All visits were separated by at least 48 hours. Participants were not familiarised to the HIIT protocols before performing them in the experimental trials.

Initial experimental visit

Prior to the experimental trials participants completed an incremental exercise test to exhaustion on an electronically braked cycle ergometer (Lode Corival, The Netherlands), to determine VO_2peak, maximum heart rate and maximal aerobic power output (W_max). The method is described fully by Scott et al. [16], but briefly, participants began cycling at 25 W for females and 60 W for males for 3 min; following this the workload was increased by 35 W every 3 min until volitional fatigue. VO_2peak was assessed using an online gas collection system (Metamax 3B, Cortex, Germany) and was defined as the highest value achieved over a 15 second recording period. HR was monitored throughout the test (Polar H10, Kempele, Finland).

Experimental visits

All experimental visits were identical except for the HIIT protocol performed. Prior to exercise a capillary blood sample was obtained from a fingertip for an immediate assessment of blood lactate (Biosen, EKD diagnostics, UK). Participants were introduced to the Feeling Scale and Felt Arousal Scale [20]. Scores on each scale were recorded immediately before and after each interval to indicate responses during the interval and at rest. Before starting the protocols all participants completed a 2-minute warm up; either 25W on a cycle ergometer (Ergo-60:60) or jogging on the spot (BW-60:60, SM-20:10 and SM-40:20). Participants were given no encouragement by the research team during the protocols, but if an exercise was being conducted incorrectly the researcher would advise/demonstrate to ensure consistency and minimise injury risk. HR was measured continuously throughout the exercise protocols (Polar H10). Following completion of the protocols (within ~1min) a post exercise blood lactate was collected. Finally, 10 minutes after completion of the protocol all participants were asked to complete the Intrinsic Motivation Inventory (IMI) [21].

Training protocols

Acute measurements were collected across four different HIIT protocols; two were evidence-based and two were accessed via the social media outlet YouTube. The Ergo-60:60 protocol has been successfully used to increase cardiorespiratory fitness in a variety of populations over a 2–12 week period (Sedentary [22], obese individuals [23], individuals with type 2 diabetes [24]). Recently this protocol has be adapted for the home environment using body-weight exercises. This adapted protocol has also been shown to induce increases in cardiorespiratory fitness in a variety of populations (sedentary [25], people with elevated cardiovascular disease risk [26], people with type 1 diabetes [27]). There are countless videos featuring HIIT on social media, as such, our aim was to choose two protocols which we felt were representative of the field. To assess the most common protocols used on social media the protocols had to meet the following criteria 1) be featured on a popular YouTube fitness channel 2) have ‘HIIT’ in the title of the video 3) take less than 20 minutes, to take advantage of the time-saving nature of HIIT 4) include body weight exercises with no equipment. The SM-20:10 protocol uses “Tabata training”, a variation of the original protocol designed by Tabata et al. [28] which has been demonstrated to increase VO_2peak. This was included as variations of “Tabata Training” are popular within social media. SM-40:20 was included as the protocol used a blend of aerobic and resistance-based exercises (e.g. press-ups) which would not typically fall under the traditional definition of HIIT, but is used by a number of videos found on social media channels.

Ergometer laboratory based HIIT (Ergo-60:60)

The laboratory-based HIIT protocol was completed on a cycle ergometer (Lode Corival), and consisted of repeated 60 second efforts of high intensity cycling at 100% W_max (obtained from the incremental exercise test) [29]. These intervals were interspersed by 60 seconds of cycling at a low intensity (50 W). Subjects completed ten high-intensity intervals. The total time commitment for the protocol (excluding warm-up) was 20 minutes.

Home-based body weight HIIT (BW-60:60)

The established body weight exercise protocol was identical to that used in Ergo-60:60, 10 repeated 60 second bouts of high intensity exercise, interspersed with 60 seconds of rest [26]. The 60 second intervals were comprised of two different bodyweight exercises performed for 30 seconds each, with no rest in between. Prior to the protocol participants were given 10 exercise pairs, which were verbally explained and demonstrated by the research team. All participants completed the same exercise pairs, 9 pairs were used with one pair completed twice (see Table 1). Participants were asked to complete as many repetitions as possible in 60 seconds. The total time commitment for the protocol (excluding warm-up) was 20 minutes.

Table 1. Summary of protocols used to measure acute responses to HIIT.

`	Number of intervals	Intensity of intervals	Interval duration (seconds)	Rest duration (seconds)	Total duration (minutes)	Work:Rest Ratio	Exercise
Ergo-60:60	10	100% Wmax	60	60	20	1:1	Cycling
BW-60:60	10	As many repetitions as possible	60	60	20	1:1	1) mountain climbers + lateral jumps 2) floor jacks + get ups 3) squat thrusts + elbow to knee 4) split squats + jogging boxers 5) burpees + jogging on the spot 6) jogging with high knees + squat jumps 7) spotty dogs + X jumps 8) jump overs + jumping jacks 9) tuck jumps + clapping jacks 10) mountain climbers + lateral jumps
SM-20:10	20	Guided by exercise video	20	10 (20s between sets)	11.5	2:1	1) Broad jumps x2 jumping jacks 2) pop squats 3) burpees with a kick 4) 3 jumps and lunge 5) squat jump slides
SM-40:20	15	Guided by exercise video	40	20	15	2:1	1) walkout press-up with shoulder taps 2) squat with knee to elbow left 3) 8 high knees and burpee 4) squat with knee to elbow right 5) kick through 6) knee to elbow plank 7) 90°squat jump 8) staggered stance push up right 9) jogging with punches 10) staggered stance push up left 11) side lunge right 12) bear crawl 13) side lunge left 14) narrow push up with arm lift 15) 180∘ burpee

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Ergo-60:60 10x60s on a cycle ergometer, with 60s rest. BW-60:60 10x 60s body weight exercises, with 60s rest. SM-20:10 20x 10s with 20s rest, exercises provided from a social media video. SM-40:20 15x 40s with 10s rest, exercises provided from a social media video.

Social media HIIT 1 (SM-20:10)

Participants followed the video https://www.youtube.com/watch?v=VhdXXqcoco0 available via the Fitness Blender YouTube Channel. The video was shown (with sound) on a television screen. The protocol consisted of 5 sets of exercise. Each set used a different exercise and was made up of 4x20s intervals, separated by 10 seconds of rest (see Table 1). Each set was then separated by 20s of rest. The total time commitment for the protocol (excluding warm-up) was 11.5 minutes.

Social media HIIT 2 (SM-40:20)

Participants followed the YouTube video https://www.youtube.com/watch?v=yz59KggOtb0) available via the Body Coach TV YouTube Channel. The video was shown on a television screen with the volume on. The protocol involved 15x40s intervals, separated by 20 seconds rest, a different exercise was used for every interval (15 exercises in total, see Table 1). The total time commitment for the protocol (excluding warm-up) was 15 minutes.

Assessment of heart rate during exercise

HR was assessed continuously throughout each protocol (Polar H10). The time of the start and end of each interval were written down and used to denote the start and end of each interval during analysis. Following each exercise session, HR data was immediately downloaded to excel for offline analysis and has been presented as a % of HRmax achieved on the incremental exercise test. Mean HR for the whole session (session HR_mean), and the highest HR achieved during each session were determined (session HR_peak). Mean and peak HR (HR_mean and HR_peak) were also determined for every interval. Mean values for each exercise session were then calculated and used to determine the interval HR_peak and interval HR_mean. The ACSM suggests that HIIT should be performed at a HR above 80% of an individual’s HR_max [30]. As such, we determined the proportion of intervals meeting the high-intensity criterion (HR >80% of max) and time spent above the criterion HR, as suggested by Taylor et al. [31].

Perceptual responses during exercise

Feeling scale and felt arousal scale

The Feeling Scale is an 11-point scale ranging from +5 to -5 [32] and is commonly used to measure affect responses (pleasure/displeasure) during exercise [14,33]. The scale presents the following verbal anchors: -5 = very bad; -3 = bad; -1 = fairly bad; 0 = neutral; +1 fairly good; +3 = good; and +5 = very good. The Felt Arousal Scale measures perceived activation along a 6-point scale ranging from low arousal (1) to high arousal (6). All participants were given standardised instructions on how to use the scale and verbal anchors were provided by one member of the research team. The participants were asked their score on each of the scales, based on their feelings at the time of completion, immediately before and after each interval.

Motivation

Intrinsic motivation inventory

The Intrinsic Motivation Inventory (IMI) is a multidimensional measurement device, which includes two subscales to assess self-reported interest/enjoyment and perceived competence. The IMI had a reported Cronbach’s alpha coefficient of 0.92 for both the interest/enjoyment scales and the perceived competence scales. All participants were asked to read the phrases in the two subscales (13 in total), and were asked to rate them on a Likert scale from 0 (not true at all) to 7 (very true). The two subscale scores were then calculated by averaging across all the items on the subscale.

Data analysis

Data is expressed as means ± SD and was analysed using SPSS Version 26.0 (Chicago, IL, USA). One subject was not able to finish the Ergo-60:60 protocol due to fatigue, therefore, the data from this participant was removed during analysis (n = 26). A one-way within subject ANOVA was used to investigate differences between protocols, for heart rate responses during exercise, change in lactate, lowest recorded score on the Feeling Scale and responses to the IMI (interest/enjoyment and perceived competence). A one-way between-subjects ANOVA was also used to assess responses to the Feeling Scale over time within each HIIT protocol. Partial eta squared (η2) was used as an estimate of effect size, with a small effect = 0.01, medium effect = 0.06, large effect = 0.14. The data from the Feeling Scale and Felt Arousal Scale were also represented in a circumplex model, which described the affective state with respect to activation (high and low) and valence (positive and negative). A Bonferroni post-hoc test was applied where appropriate. Significance was set at P≤0.05.

Results

Physiological responses to exercise

Heart rate

Mean HR traces for each protocol are shown in Fig 1. At the start of the protocols, immediately following the warm up, there were no significant differences in baseline HR responses between the protocols (P = 0.532). There was a significant effect of protocol on interval HR_peak (P = 0.018, η_p² = 0.238), although following post-hoc analysis no significance was found between the HIIT protocols (P>0.05). Interval HR_mean was not different between protocols (P = 0.203, η_p² = 0.111). There was also no difference between HIIT protocols for session HR_peak (P = 0.315, η_p² = 0.060) or session HR_mean (P = 0.015, η_p² = 0.238). There was a significant effect of protocol on the proportion of intervals meeting the ACSM high-intensity exercise criterion (HR >80% of maximum HR) (P = 0.005, η_p² = 0.265), with the criterion being achieved more regularly during BW-60:60 than SM-20:10 (P = 0.039), but no further differences observed during Ergo-60:60 or SM-40:20. There was also a significant effect of protocol on time spent above the criterion HR (HR >80% of max) (P<0.001, η_p² = 0.488), with participants spending significantly less time above 80% of HR_max in SM-20:10 (8±3mins) than all other protocols (Ergo-60:60: P = 0.034, BW-60:60: P = 0.006, SM-40:20: P = 0.006), but no further differences between protocols. Data is presented in Table 2.

Table 2. Heart rate (HR) responses to the HIIT protocols.

	Ergo-60:60	BW-60:60	SM-20:10	SM-40:20	P Value
Session HR_peak (%)	94±4	95±4	93±6	94±4	P = 0.315
Session HR_mean (%)	84±6	83±4	83±9	84±5	P = 0.765
Interval HR_peak (%)	90±5	90±3	84±7	87±4	P = 0.018
Interval HR_mean (%)	85±6	83±4	81±9	84±4	P = 0.203
HR ≥80% max (min)	13.9±4.9^*	13.5±3.5^*	7.7±3.1	12.1±2.4^*	P<0.001
Proportion of intervals meeting a HR ≥80% max (%)	87±16	93±10^*	74±20	88±15	P = 0.005

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Values are mean ± SD.

*Represents significant difference from SM-20:10 (P<0.05). Session HR_peak: Maximum heart rate achieved during the whole exercise session. Session HR_mean: Mean heart rate achieved during the whole exercise session. Interval HR_peak: Average maximum heart rate achieved during each of the intervals only. Interval HR_mean: Average mean heart rate achieved during each of the intervals only. HR ≥ 80% max: Time spent above or equal to the high-intensity criterion (80% of maximum heart rate). Proportion of intervals meeting a HR ≥ 80% max, proportion of the intervals meeting the high-intensity criterion (≥80% of maximum heart rate).

Blood Lactate

There was no significant differences in baseline blood lactate between the protocols (P = 0.218). Change in blood lactate was significantly different between protocols (P<0.001, η_p² = 0.239), SM-20:10 resulted in a significantly lower change in blood lactate concentration (5.5±2.6mmol/L) compared to Ergo-60:60 and BW-60:60 (7.4±2.6mmol/L and 7.7±3.7 mmol/L, P = 0.002 and P<0.001 respectively). There were no further differences between protocols (P>0.05; Fig 2).

Fig 2 — † Represents significant difference from Social-Media-1 (SM-20:10) (P<0.05).

Perceptual responses during exercise

Feeling scale

The minimum reported Feeling Scale score was similar across all protocols (P = 0.268, η_p² = 0.051; Fig 3A). Detailed information regarding Feeling Scale scores over time for each protocol is presented in Fig 3B, importantly markings on the figure represent significant changes compared to the following intervals. Feeling Scale scores immediately before the interval are also presented in Fig 3B. The Feeling Scale scores decreased in a linear manner after interval 5 during Ergo-60:60 and interval 6 during BW-60:60 (Fig 3Bi and 3Bii. The response to SM-20:10 and SM-40:20 was more complex with large variations present (Fig 3Biii and 3Biv).

Circumplex model

In order to investigate the nature and the magnitude of affect changes that occur in response to acute exercise stimuli a circumplex model was used. In a circumplex model of affect the horizontal axis represents affective valence (negative to positive) and the vertical axis represents the degree of perceived activation (low to high). Based on visual inspection, the patterning of Feeling Scale and Felt Arousal Scale values between Ergo-60:60 and BW-60:60 was similar within the circumplex model depicted in Fig 4A and 4B. During Ergo-60:60 and BW-60:60 the Feeling Scale shifted left toward greater displeasure after each interval, and Felt Arousal Scale shifted up towards a high arousal during the protocols, but only reached the activated pleasant or ‘energy’ quadrant after the 9^th interval (out of a total of 10 intervals). SM-20:10 and SM-40:20 initially followed this pattern, however past interval 11 in SM-20:10 (out of a total of 20 intervals) and the 9^th interval in SM-40:20 (out of a total of 15 intervals) the results fluctuate (Fig 4C and 4D). Unlike all other protocols, SM-20:10 remains in the unactivated pleasant or ‘calmness’ quadrant throughout the session.

Fig 4 — A. Ergo-60:60 B. BW-60:60 C. SM-20:10 D. SM-40:20. Values on the line represent the interval number when measurement was taken.

Motivational responses to exercise

Intrinsic motivation inventory

The subscale score for interest/enjoyment was significantly different between protocols (P = 0.006, η_p² = 0.158), BW-60:60 reported significantly higher scores (5.0±1.2) on the interest/enjoyment subscale compared to Ergo-60:60 (4.4±1.2, P = 0.020) and SM-40:20 (4.3±1.2, P = 0.008), with no other significant differences between the protocols (P>0.05; Fig 5A). The subscale score for perceived competence was significantly different between protocols (P<0.001, η_p² = 0.226), BW-60:60 and SM-20:10 reported significantly higher scores (3.8±0.9, P = 0.005 and 4.1±1.1, P = 0.001 respectfully) on the perceived competence subscale compared to SM-40:20 (3.2±1.1), with no other significant differences between the protocols (P>0.05; Fig 5B).

Fig 5 — * represents significant difference from BW-60:60 (P<0.05). + represent significant difference to SM-40:20 (P<0.05).

Discussion

The main finding of the present study is that important acute physiological, perceptual and motivational differences exist between HIIT protocols developed for social media platforms and those shown to be effective in academic literature. In addition, our data suggests higher physiological responses experienced during HIIT are not a key determinant of post-exercise enjoyment or feelings of competence. Finally, in contrast to traditional HIIT protocols performed on a cycle ergometer, protocols performed using body-weight exercises result in more complex perceptual responses during exercise, which do not correlate with HR responses. Therefore, application of traditional models (e.g. Dual-theory) may not be appropriate to describe the perceptual responses to body-weight HIIT. Future research should seek to investigate the physiological and perceptual responses to exercise throughout a body-weight HIIT intervention to determine long-term feasibility and effectiveness within a real world setting.

Physiological responses to exercise

This is the first study to compare the physiological responses to popular HIIT workouts found on social media with established evidence based protocols [26,29]. Social media workouts are an attractive and popular alternative to traditional forms of HIIT; SM-20:10 and SM-40:20 have over 6 million views on YouTube, but research into their effectiveness is lacking. Recent work [8,9,34] suggests that acute physiological responses may dictate long-term training outcomes to HIIT. Therefore, a comparison of these social media protocols to those already established as effective in a research setting provides important information for consumers and fitness professionals.

Interestingly, similar HR and blood lactate responses were seen when comparing the two established protocols (Ergo-60:60 and BW-60:60), despite the different modalities of exercise (cycle ergometer vs body-weight). Furthermore, despite visible differences in the mean HR traces (Fig 1) there were no acute physiological differences between the established protocols and SM-40:20. In contrast a number of significant differences (lower change in lactate, less time spent above the criterion HR, and lower proportion of intervals meeting the criterion HR (>80 of max)) were observed between SM-20:10 and the established protocols. Moholdt et al. [34] reported greater increases in VO_2peak in patients who achieved a higher HR_mean during HIIT intervals (12 weeks, 4x4min at 85–95% HRmax with 3 mins rest at 60–70% HRmax), in patients with coronary heart disease. In addition, recent studies have suggested that lactate accumulation during HIIT is linked to the magnitude of the physiological adaptations. Hoshino et al. [9] administered mice with dichloroacetate (DCA), a pyruvate dehydrogenase activator which reduces muscle and blood lactate concentrations during and after exercise, over a 4 week HIIT period (10x60s high intensity treadmill running with a 1 min rest). Chronic DCA administration attenuated exercise-induced metabolic adaptations, including increases in mitochondrial enzyme activity (CS and b-HAD) and protein content (COXIV) compared to control animals (saline), suggesting that repeated lactate accumulation during HIIT is important for training–induced mitochondrial adaptations. Furthermore, Fiorenza et al. [8] found that speed endurance exercise (18x5s “all-out” efforts interspersed with 30s of passive recovery) increased PGC-1α mRNA response compared to work matched repeated-sprint exercise (6x20 s “all-out” with 120 s of passive recovery). Importantly, speed endurance exercise was associated with higher muscle lactate accumulation and lower muscle pH, suggesting that that greater metabolic perturbations with high lactate accumulation contributed to the enhanced PGC-1α mRNA response. As such, it is hypothesised that the lower time spent above the criterion HR (>80% of max) and change in lactate observed with SM-20:10 compared to the other protocols will reduce its long-term effectiveness. However, the data would suggest that body-weight exercises can be used as an effective HIIT modality, capable of eliciting similar acute physiological responses to HIIT performed on a laboratory cycle ergometer. Furthermore, protocols available via social media platforms can result in similar acute physiological responses, but fitness professionals need to proceed with caution when prescribing these protocols as they are not all equal. Interestingly, the lower lactate responses observed following SM-20:10 may have been due to the reduced interval duration as previous research in regional-level cyclists reported higher blood lactate responses after longer intervals (90s and 130s) compared to shorter 10s interval [35].

Perceptual responses to exercise

Dual-Mode theory suggests affect experienced during exercise is influenced, in part, by the metabolic demand associated with the exercise [12]. However, in the current study the lowest recorded value on the feeling scale was not different between the protocols, despite significant differences in the physiological responses. This data contrasts with previous comparisons of HIIT protocols where findings have shown greater physiological strain is associated with lower affective responses [23,36], supporting the application of Dual-Mode theory for HIIT. Although the exercise intensity was different between HIIT protocols the same interval duration and work-to-rest ratios were employed in these earlier studies [23,36]. This contrasts with the current study where work-to-rest ratio and interval duration were different between the protocols. The potential importance of interval duration and work-to-rest ratio in determining affective response to HIIT is supported by recent research [37,38]. Martinez et al. [38] demonstrated that shorter intervals (30 and 60 seconds) had similar affective responses, but longer intervals were perceived as more aversive (120 seconds). Wood et al.[37], showed no difference in affect when comparing a HIIT and SIT protocol, despite significantly greater lactate accumulation experienced during SIT. Importantly, the work-to-rest ratio and interval duration used in the HIIT and SIT protocols were again different (60 second intervals and a 1:1 work-rest-ratio in HIIT; and 30 second intervals and a 1:3 work-to-rest ratio in SIT). As previously suggested by Jung et al. [39], these studies may suggest that work-to-rest ratio and interval duration could influence affective response to HIIT, and that manipulating these factors could interfere with the utility of Dual-Mode theory for HIIT.

It is also important to note that Ergo-60:60 imposed a fixed intensity (100% W_max) on participants, whereas the other protocols used all-out but self-paced intensities. The aim of the current research was not to compare imposed vs self-selected intensities, as different exercise modalities were used (cycling vs. body-weight exercises). However, Kellogg et al. [40] demonstrated that self-paced HIIT resulted in more negative affect (FS) than fixed intensity HIIT, when cycling was used (both protocols 8x60s work with 60s rest). Therefore, it is possible that the intensity regimes (imposed vs self-selected) could have influenced the perceptual responses observed in the current study.

As well as the magnitude of the peak negative or positive affect, Decker and Ekkekakis [41] suggests that the rate of change in affect occurring during the exercise is also important. Previous studies employing cycling [37,42–44] or running [45,46] have consistently reported that affect becomes less positive during exercise in response to acute HIIT. This finding was echoed in a scoping review of the literature by Stork et al. [47], who noted that nearly all of the studies assessing in-task affect have shown a significant decline during HIIT. This profile is shown in both Ergo-60:60 and BW-60:60, where in-task affect shows a significant decline from interval 5 onwards. In contrast, SM-20:10 and SM-40:20 do not show a significant fall in affect from the first to last interval and changes in affect show no obvious pattern. The circumplex model, which incorporates affective valence and perceived activation to give a more complete view of affective responses during exercise [48], also highlights the difference in affect responses when using the two social media videos. It is unclear what is causing this difference between the protocols, however the social connection within social media HIIT (e.g. led by an influencer), and how the influencer interacts with the audience may have altered the enjoyment or perception of the unpleasant exercise [49]. Therefore, future studies should look to investigate the influence of exercise videos, interval duration, work-to-rest ratio and the use of body-weight exercises on in-task affect.

Motivation and enjoyment

This is the first study to compare post-exercise enjoyment of HIIT protocols employing different exercise modalities. In their scoping review Stork et al [47] cautioned that people’s experiences during one form of interval exercise may not be the same as another. Our data provides novel evidence supporting this argument, identifying that participants reported greater enjoyment when HIIT was performed using body-weight exercises (BW-60:60) compared to a cycle ergometer (Ergo-60:60). Importantly, BW-60:60 and Ergo-60:60 (matched for interval duration and work-to-rest ratio) produced similar HR traces and overall physiological responses, suggesting that the exercise mode could be an important factor in the differential enjoyment. Interestingly, BW-60:60 was also more enjoyable than SM-40:20, despite body-weight exercises being employed during both protocols. The greater enjoyment experienced could have been influenced by the lower competence for completing SM:40:20 compared to BW-60:60. It is possible that the specific exercises employed during BW-60:60 and SM-20:10 were responsible for the greater perceived competence following these protocols compared to SM-40:20. Unlike BW-60:60 and SM-20:10 which used entirely whole-body exercise, SM-40:20 employed a combination of whole-body and upper body exercise. Additionally the social media influencer may have had a part to play in creating perceptions of competence via the description of the exercises, encouragement provided and behaviour change techniques [50]. This observation may prove important to exercise professionals when designing HIIT protocols, as people are inherently drawn to engage in behaviours that they feel competent to carry out [51].

Limitations

It is important to note that the current study was conducted in young recreationally active participants, with a relatively small sample size (n = 27). A younger population may find social media based approaches more acceptable and relevant than other populations, as such, we are unable to generalise our findings to older physically inactive individuals. We are also unable to generalise our findings to other HIIT protocols used within research or available on social media. All sessions were completed in a lab environment, rather than traditional environments used for body weight exercises (home, gym or local park). Finally, there is a diverse range of videos available on social media, and features unrelated to HIIT (e.g. likeability and relatedness of the influencer) may cause individual changes to perceptual responses. Investigating these factors was beyond the scope of the current study, but should be investigated in future work. However, the work still represents an important step forward in our understanding of HIIT as it is the first study to explore the differences between established evidence-based protocols and workouts with millions of views on social media. Given the importance of social media influencers for impacting health [6] and the popularity of HIIT on social media it is important that future research continues to consider the potential effects of such protocols.

Conclusions

This study shows that HIIT protocols available on social media offer an interesting real-world alternative for promoting exercise participation. However, the public and fitness professionals need to evaluate HIIT protocols promoted on social media with care, as not all will produce comparable acute physiological responses to evidence-based HIIT. In addition, the study demonstrates significant differences in the rate of change in affect between the social media protocols and those established within the literature. Future studies should look to investigate these differences further to explore if the social connection or interaction with the audience created by influencers may be responsible for the difference. Finally, the study also showed enjoyment of HIIT may be influenced by exercise mode, body-weight vs. Ergometer. Therefore, this study is an important first step in evaluating how HIIT protocols promoted by social media compare to evidence based protocols with research to support their efficacy to improve cardiorespiratory fitness. Future studies should continue to investigate these highly popular and practical HIIT protocols, including their long term effects on exercise adherence and health outcomes.

Data Availability

All relevant data are within the paper, and files are available in the LJMU database (DOI: https://doi.org/10.24377/LJMU.d.00000099).

Funding Statement

The authors received no specific funding for this work.

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PLoS One. doi: 10.1371/journal.pone.0257685.r001

Decision Letter 0

Kathryn L Weston

3 Jun 2021

PONE-D-21-08687

Evidence-based vs. social media based high-intensity interval training protocols: physiological and perceptual responses

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Reviewer #1: Thank you for the opportunity to review this paper. This paper presents a randomised cross-over trial, exploring the acute physiological and perceptual responses to four high-intensity interval training protocols. I enjoyed reading this interesting paper, and feel it will be a novel contribution to the evidence base. I do however have a number of comments detailed below for the authors consideration.

Major comments

In this study, heart rate is used to explore exercise intensity. The authors present their findings as a percentage of maximal heart rate (HRmax). While this information is not included in the methods, it appears from information presented in Table 2 that the authors used predicted HRmax using the formula 220- participants age. However, as part of the first experimental visit, participants undertook an incremental exercise test until exhaustion, with heart rate monitored throughout. I wondered why, given the limitations associated with HRmax predictions, the authors chose to use this when they had access to heart rate data from the VO2max test, where presumably a maximum heart rate was recorded? I would have preferred to see the use of HRmax from the VO2max test, rather than predicted HRmax, if possible. If this data is not available, the use of predicted HRmax should be described in the methods, and should also be discussed as a limitation in the discussion.

Line 79-83: Here the authors begin to justify their selection of evidence-based and social media HIIT protocols, which I commend and think is central to the paper. I think this information might be better placed in the methods section (perhaps line 188 under the heading Training Protocols). It would also be useful to further explain why these protocols were chosen. Have the evidence-based protocols been shown to improve health/ fitness outcomes? Additionally, why specifically where the social media protocols/ videos selected?

In terms of the rest of the paper, my main comments centre around ensuring that the information presented is clear for an individual not involved in the project, or not overly familiar with HIIT research. I have provided more detail as to where I think this detail could be added below.

Minor comments

Abstract:

Perhaps the first line of the abstract could focus on the evidence base surrounding the effects of HIIT on health/ fitness, rather than the popularity of HIIT with social media influencers?

Line 23: could mean peak heart rates as a percentage of max heart rate for each protocol be included in the abstract?

Introduction

Line 33: a definition of HIIT would be useful in the first paragraph of the introduction.

Line 41: It may be useful to point out that some HIIT protocols may not be classed as HIIT given the traditional definition of HIIT. Or that it is unknown if these social media protocols are classed as HIIT. This might further justify the conduct of this study.

Line 66: in the section around Dual Mode Theory- it might be useful to point out that the majority of work which DMT is based on use continuous high intensity exercise- not HIIT.

Line 70: I believe Self Determination Theory needs capital letters. Additionally, I think a reference to Deci and Ryans work on SDT would be useful here.

The novelty of this study could be made clearer in the introduction. Perhaps exploration of the literature exploring the acute effects of other HIIT protocols could be used to justify why it is important to explore acute effects of HIIT before prescribing it in an intervention?

Methods

Line 85- how were participants recruited?

Line 86- is there a reference that could be cited here for the definition of recreationally active?

Line 135- I am not sure if I am correct here, but do the YouTube videos used need to be attributed to specific YouTube channels/ do the names of the channels need to be stated in the manuscript?

Line 156- I would prefer to see slightly more detail on the methods undertaken to explore time spent at or above the criterion high-intensity heart rate here. Weston describes both per protocol and intention to treat analysis protocols, so it would be useful to state which method was undertaken.

I may have missed it, but when was the IMI administered?

Results

Rather than stating just the p-values in the text of the results section, it would be useful to also present means/ mean differences and standard deviations or confidence intervals, depending on the data. This would allow the authors to explore the clinical/ practical significance of the findings in more detail, rather than relying solely on statistical significance.

Line 201- I commend the authors for exploring the HR data using processes outlined by Weston et al., (2015). For the data exploring the proportion of high-intensity repetitions spent at or above the high intensity criterion (e.g. 80% HRmax), could the authors consider reporting these findings as outlined in Weston et al. 2015. For example (taken directly from the abstract of Weston et al., 2015):

“…the median (interquartile range) proportion of repetitions meeting the high-intensity criterion was 58% (42% to 68%).”

Figure 1 is very useful to visualise the variation of data around the mean. For readers who are unfamiliar with this type of figure, could the authors consider stating in the key that the grey shading is the SD and black line is the mean HR?

Line 243: It would be useful here to clarify for the reader how many intervals were completed in each protocol, to avoid them having to return to the methods. E.g. after the 9th interval (out of a total of X number of intervals).

Discussion

It would be useful when interpreting the results to explore the practical or clinical meaningfulness of the findings rather than relying on statistical significance. For example, in Figure 5, the difference in perceived competence between groups appears to be about 0.5 to 1 point, while this is statistically significant, is it practically or clinically meaningful? Are participants likely to notice this difference? Is there a minimum clinically important difference for this scale that could be explored?

Line 284- what is the definition of a considerable difference? Have the authors defined this previously?

Line 285- is Figure 2 the correct figure to be referring to here?

Line 287- an overview of what these differences were would be useful here.

Line 287-293 seems to be repetition from the introduction. Could this section be summarised more briefly given that these papers are discussed in the introduction?

Line 309- what does mimic acute physiological responses mean?

Line 334- The use of DMT for HIIT has been critiqued previously (See Batterhams argument in Biddle and Batterham 2015 https://doi.org/10.1186/s12966-015-0254-9). Most dual mode studies are conducted using continuous high intensity exercise, not interval exercise. Your findings seem to support the notion that affective responses could be different for interval exercise, despite the intensity. Or Jung et al., 2016 may be useful doi: 10.3389/fpsyg.2015.01999

Line 348: The authors state that the research team gave no encouragement to participants during the intervals apart from providing advice on correct technique. I would like to understand why this decision was made? In the videos used for the social media HIIT protocols, the facilitators provide generalised words of encouragement and some level of human interaction. I realise this could not have been completely standardised across the participants for the evidence based protocols, but perhaps the authors could consider whether this human interaction and encouragement in the social media videos may have impacted on enjoyment in comparison to no encouragement at all in the evidence based protocols.

Line 352: Should this section be named motivation or enjoyment? It is named motivation but seems to discuss enjoyment more.

Line 374: Could the authors consider adding in that the findings cannot be applied to other HIIT protocols or modalities?

Line 385- research led HIIT or evidence-based HIIT- would be useful to be consistent throughout the paper.

Line 392- I think this sentence may need further clarity. How do the findings show how HIIT can be used to promote exercise?

Reviewer #2: PLOS ONE-d-08687

Evidence-based vs. social media based high-intensity interval training protocols:

physiological and perceptual responses

General comments: I was excited to read this work as I have conducted some research in this area and am always eager to read what others lab are doing in this area. This study is well-rationalized, follows proper methods, and the presentation of the Results and subsequent explanation are sound. Findings will be of interests to scientists and clinicians who use interval exercise in their facilities.

Specific comments: Please respond to the comments listed below regarding your paper—thank you.

Abstract—this is well written, yet I have one comment to make in line 28. You do not present HR data so how can you conclude that these social media based protocols are feasible? Only if HR attains 85 %HRmax are these protocols truly eliciting intensities equivalent to lab based HIIT?

Methods—this is not a criticism but more a question—these protocols are not matched for work and have different structure, duration, etc., so how does this alter the interpretation of these data, as clearly the differences in these traits alter the magnitude of physiological and perceptual stress experienced?

Line 179: Please confirm that this was a two-way ANOVA comparing differences in these variables across time as well as bout; thank you.

Line 105: the 10 X 1 cycling protocol is prescribed according to Wmax-PPO, yet there is no text here denoting how this was done. Also, there is no mention of text in this section describing the fed state of participants pre-session, if time of day was standardized, if PA was prohibited prior to testing, etc.?

Were any practice sessions allotted to the participants to improve their familiarity with these body weight exercises?

Were the instructions on how to interpret FS standardized and was the same experimenter tasked with recording this outcome in each session?

I recommend that the Authors present some type of ES value in their Results to denote the meaningfulness of any differences—thank you.

Results—line 199—is there a reason why predicted HRmax is used here when your baseline VO2max test allows you to actually assess true HRmax? Please clarify this.

Line 219—I believe this text needs some additional p values to better articulate the statistical results; thank you.

Also I believe that some of this text needs to be substituted by data from similarly habitually active participants rather than mice or trained cyclists, who have different exercise tolerance, BLa accumulation, etc. https://pubmed.ncbi.nlm.nih.gov/28737586/

I also believe you need to talk about the fact that the 10 X 1 regimen is at a fixed intensity; whereas, the other protocols are all-out or self-paced. Thus, the first regimen is imposed upon each participant; whereas, in the other 3 sessions, the exerciser has total control of his/her effort exerted. There is work showing that this feature can alter perceptions of exercise, so perhaps a few lines of text needs to be included here acknowledging this attribute.

Reviewer #3: This is an interesting study examining acute physiological, perceptual and motivational responses to popular social media HIIT protocols in comparison to evidence-based HIIT protocols. I commend the researchers for their novel study, which is particularly timely given many people’s time at home has been significant during the past year and interest in social media based workouts has also increased.

The manuscript is very well written, with a strong and balanced discussion including key studies in this field and highlighting opportunities for future research.

You may wish to consider the points below:

Methods:

It would be useful to include further details regarding the four HIIT protocols. For example, where were the social media HIIT sessions completed? In the lab? Details of a warm-up were provided, however did participants also complete a cool-down?

In addition to the popularity of the YouTube clips, what considerations were made when choosing these two HIIT workouts?

Discussion:

It might be useful to consider the venue in which HIIT sessions were conducted when explaining findings. Enjoyment and motivation may differ for a lab based session in comparison to other venues (e.g. home, gym, outdoors, etc.). In addition, the variety of exercises included for the social media and BW HIIT protocols, in comparison to using only the cycle ergometer, may also explain differences in enjoyment and motivation. The age of participants might also be considered, as younger adults may find social media based PA approaches more acceptable and relevant than other age groups.

Limitations:

Participants being classified as recreationally active has been noted as a limitation of the study, however the sample size has not been mentioned.

**********

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PLoS One. 2021 Sep 29;16(9):e0257685. doi: 10.1371/journal.pone.0257685.r002

Author response to Decision Letter 0

11 Aug 2021

We thank all of the reviewers for their valuable time and feedback. The comments provide have all been addressed. Any changes have been highlighted in red in the text and summarised below.

Major comments

In this study, heart rate is used to explore exercise intensity. The authors present their findings as a percentage of maximal heart rate (HRmax). While this information is not included in the methods it appears from information presented in Table 2 that the authors used predicted HRmax using the formula 220- participants age. However, as part of the first experimental visit, participants undertook an incremental exercise test until exhaustion, with heart rate monitored throughout. I wondered why, given the limitations associated with HRmax predictions, the authors chose to use this when they had access to heart rate data from the VO2max test, where presumably a maximum heart rate was recorded? I would have preferred to see the use of HRmax from the VO2max test, rather than predicted HRmax, if possible. If this data is not available, the use of predicted HRmax should be described in the methods, and should also be discussed as a limitation in the discussion.

Originally the manuscript presented data as a percentage of predicted HRmax (220-age) to replicate the real world application of using social media HIIT (i.e. home-based exercise in those without access to formal physiological testing). However, the authors agree that in this context the HRmax acquired from the VO2max test would result in greater insight into the acute responses. Figure 1 and Table 2 have been updated to reflect these changes, and statical analysis has been reproduced. Following these changes, post-hoc analysis did not show a significant difference between protocols when HR was expressed as interval HRpeak (line 233). Significance remained the same for time spent >80%HRmax and proportion of intervals meeting a HR ≥80% max. This change to the results has resulted in some minor changes to the text in the discussion, but we do not believe that the conclusions drawn have been affected, as such, these have not been amended.

We thank the reviewer for this suggestion and as suggested have moved this information to the methods (line 137). In addition, the new paragraph within the methods under the heading of ‘Training Protocols’ now provides greater insight into why the protocols were selected. In brief, we used 4 criteria to assess videos found on YouTube 1) had to be featured on a popular YouTube fitness channel 2) have ‘HIIT’ in the title of the video 3) take less than 20 minutes, to take advantage of the time-saving nature of HIIT 4) include body weight exercises with no equipment. From these videos the SM-20:10 protocol was included as the video uses “Tabata training”, a variation of the original protocol designed by Tabata et al. (1996) which has been demonstrated to lead to increases in VO2peak. SM-40:20 was included as the protocol used a blend of aerobic and resistance-based exercises (e.g. press-ups) which would not typically fall under the traditional definition of HIIT, but is used by a number of videos found on social media channels.

Minor comments

Abstract:

Perhaps the first line of the abstract could focus on the evidence base surrounding the effects of HIIT on health/ fitness, rather than the popularity of HIIT with social media influencers?

Line 11 within the abstract now reads “High intensity interval training (HIIT) is a time-efficient exercise modality to improve cardiorespiratory fitness, and has been popularised by social media influencers.” We hope this presents the evidence base for HIIT but also refers to the role of social media influencers, which, we believe is important in the context of our work.

Line 23: could mean peak heart rates as a percentage of max heart rate for each protocol be included in the abstract?

Due to the updated analysis requested by the reviewers (the use of actual HRmax used rather than predicted HRmax), percentage of intervals achieving a heart rate greater than 80% HRmax has now been used within the abstract. The values for BW-60:60 and SM-20:10 have been added (Line 25), however adding any additional data within the abstract would exceed the abstract word count and would result in an unclear message for an abstract. The abstract now includes all data surrounding the time spent above 80%HRmax for each protocol (Line 28).

Introduction

Line 33: a definition of HIIT would be useful in the first paragraph of the introduction.

A definition has been added to the introduction (line 38) “High intensity interval training includes brief, intermittent bursts of vigorous activity (typically between 80-100% HRmax), interspersed by periods of rest or recovery (1).”

Thank you for your comment we agree that our rationale for investigating social media HIIT protocols could be better developed within this paragraph. Therefore, we have added further information here (line 57), including the observation that many social media protocols do not use interval durations and/or work-to rest ratios that have been backed by research. In addition, many social media protocols use a combination of aerobic and resistance exercises which we do not believe meet the research backed definition of HIIT.

Line 66: in the section around Dual Mode Theory- it might be useful to point out that the majority of work which DMT is based on use continuous high intensity exercise- not HIIT.

The following statement has been added to the introduction (Line 83): “However, the majority of work used to support Dual Mode Theory has been carried out using continuous high intensity exercise, and its use within HIIT has been critiqued previously (15).”

Line 70: I believe Self Determination Theory needs capital letters. Additionally, I think a reference to Deci and Ryans work on SDT would be useful here.

Thank you - SDT has been capitalised (Line 87), and the citation for Deci and Ryan (2000) has been added to Line 89.

Line 70: I wonder why specifically SDT is discussed here? While there are other theories of motivation, it might be useful to clarify that SDT has been used to predict/ explore/ enhance physical activity/ exercise behaviour? E.g., Teixeira et al., (2012) https://hes32-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=https%3a%2f%2fdoi.org%2f10.1186%2f1479%2d5868%2d9%2d78&umid=2ba797c4-0763-42b4-9ef0-d2ada0e77048&auth=768f192bba830b801fed4f40fb360f4d1374fa7c-d09700cffeed5beae5d926dd1a8b45900ac6a33e

We agree the link could have been made clearer within this section as it reflects the potential for HIIT protocols with positive changes to perceived competence and autonomy to influence future exercise participation. We have therefore edited this section (Line 85-90) to improve clarity of the argument.

As far as we are aware, several studies have investigated people’s attitudes and intentions toward interval exercise, but none have tested if these variables can predict subsequent interval exercise behaviour. Therefore the acute responses to affect are only theory-driven, although we agree that future theory-driven research is needed to address questions regarding perceptual responses, interval exercise, and long-term behaviour.

Methods

Line 85- how were participants recruited?

Participants were recruited from Liverpool John Moores University via internal emails and posters. This information has been added to Line 101.

Line 86- is there a reference that could be cited here for the definition of recreationally active?

To our knowledge there is no accepted definition of recreationally active, but in our study it was greater than 1 but less than 4 structured exercise sessions per week. This is similar to what was used in previous studies (e.g. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3761819/). As this is not a formal definition we have not added a reference here.

Line 135- I am not sure if I am correct here, but do the YouTube videos used need to be attributed to specific YouTube channels/ do the names of the channels need to be stated in the manuscript?

We have added which YouTube channel the HIIT videos were featured on to Line 172 and Line 179.

When addressing the reviewers comments on the manuscript we realised that there has been an amendment to Westerns et al. The reference should now be cited as Taylor et al, this has been amended in the text.

The authors interpretation of the guidelines presented in Taylor et al. (2015) are that these are for use within intervention studies, where assessment of session attendance and compliance with the prescribed protocol are crucial. As such, in Taylor et al. (2015) the intention to treat analysis includes analysis of training sessions regardless of if they were completed or not (a value of 40% of maximal heart rate was imputed for cases where heart rate data were missing due to participant absence), whereas, per protocol analysis included only sessions that were completed. The use of intention to treat analysis in this context is crucial to quantify the overall dose of the intervention, whereas the per protocol analysis provides information on intervention fidelity. As our study is an acute assessment of 4 HIIT protocols we do not believe that the use of intention to treat or per protocol analyses is warranted or intended by Taylor et al. We believe that this difference is rather complex and as such the current manuscript would not benefit from discussion of the different statistical approaches taken.

I may have missed it, but when was the IMI administered?

This has been added to Line 135 for clarity “10 minutes after completion of the protocol”

Results

For the heart rate data, we feel as though these values are better represented within the table as the clarity of the data interpretation was compromised when all data was included within the text. However following the suggestions from reviewer 2 we have added means to the results section when they are presented as a figure, and have also added effect sizes to the results, which allows for meaningfulness of any differences to be interpreted.

“…the median (interquartile range) proportion of repetitions meeting the high-intensity criterion was 58% (42% to 68%).”

Our aim was to use the guidance provided by Taylor et al (2015) as this the only paper to provide recommendations on reporting HIIT interventions. However as mentioned in our previous comment the aim of Taylor et al (2015) was to provide intervention fidelity. We believe that the median was used in Taylor et al due to the lack of data recorded during the intervention, as such they replaced missing HR values with 40%. However our data is from 4 acute session therefore we believe that presenting the mean±SD is more relevant within the context of our work.

Added to the legend of Figure 1“Black solid line represents Mean and the grey shaded area the SD.”

This additional detail has been added for each of the protocols (Line285-287).

Discussion

To our knowledge there isn’t a clinical significance for these values as they are dependent on each individual. Although we have now included effect sizes within the results section to indicate the meaningfulness of any differences, which previous work investigating acute responses to HIIT have also included. We agree that future studies are needed to investigate the effect perceptual variables have on adherence, and to provide reference values as a result.

Line 284- what is the definition of a considerable difference? Have the authors defined this previously?

This has been edited to ‘visual differences’ rather than ‘considerable difference’, as we agree the phrase ‘considerable’ is not clear/descriptive of the data presented. The aim of this sentence was to bring attention to the visual differences in the heart rate traces during the different protocols.

Line 285- is Figure 2 the correct figure to be referring to here?

Thank you for pointing this out, updated to Figure 1

Line 287- an overview of what these differences were would be useful here.

We have added information that lower change in lactate, less time spent above 80% HRmax and a lower proportion of intervals spent above 80%HRmax were the differences observed (Line 333). -

Line 287-293 seems to be repetition from the introduction. Could this section be summarised more briefly given that these papers are discussed in the introduction?

We feel this section is more impactful and clearer has part of the development of the discussion. But agree it was repetitive of the text used in the introduction, therefore we have edited the introduction to summarise the literature to prevent duplication (Line 62).

Line 309- what does mimic acute physiological responses mean?

We agree that the choice of wording could have been clearer, this has been changed to “result in similar” to improve clarity (Line 358).

Line 334- The use of DMT for HIIT has been critiqued previously (See Batterhams argument in Biddle and Batterham 2015 https://hes32-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=https%3a%2f%2fdoi.org%2f10.1186%2fs12966%2d015%2d0254%2d9&umid=2ba797c4-0763-42b4-9ef0-d2ada0e77048&auth=768f192bba830b801fed4f40fb360f4d1374fa7c-03e42631fbed81d32922dee497184693e18d7952). Most dual mode studies are conducted using continuous high intensity exercise, not interval exercise. Your findings seem to support the notion that affective responses could be different for interval exercise, despite the intensity. Or Jung et al., 2016 may be useful doi: 10.3389/fpsyg.2015.01999

Thank you, this has been added to line 381.

We did not provide encouragement to participants during the protocols as we wanted to replicate the home-based environment that these protocols would be used in. There are no videos currently available for the evidence based protocols, as such, if these were completed by participants at home they would have no encouragement. We believe that we have commented on the potential role of human interaction in the social media protocols in lines 424 of the discussion, but have added more information to line 438 in the limitations.

Line 352: Should this section be named motivation or enjoyment? It is named motivation but seems to discuss enjoyment more.

We agree that this sections primarily discusses enjoyment, however it also presents results from the IMI which includes perceived competence. We have therefore updated the section to ‘Motivation and Enjoyment’ to more accurately reflect the content (Line 209)

Line 374: Could the authors consider adding in that the findings cannot be applied to other HIIT protocols or modalities?

This had been added to the limitations (line 434)

Line 385- research led HIIT or evidence-based HIIT- would be useful to be consistent throughout the paper.

Changed to evidence based throughout

Line 392- I think this sentence may need further clarity. How do the findings show how HIIT can be used to promote exercise?

We agree that this statement was rather vague and have changed it to read, “this study is an important first step in evaluating how HIIT protocols promoted by social media compare to evidence based protocols with evidence to support their efficacy to improve cardiorespiratory fitness” (Line 457).

Reviewer #2: PLOS ONE-d-08687

Evidence-based vs. social media based high-intensity interval training protocols:

physiological and perceptual responses

Thank you for your review and valuable feedback, the comments provide have all been addressed. Any changes have been highlighted in red in the text and summarised below.

Due to the updated analysis requested by the reviewers (the use of actual HRmax rather than predicted HRmax), percentage of intervals achieving a heart rate greater than 80% HRmax has now been used within the abstract. The response to each protocol has been added to the abstract (Line 25).

Introduction—so the last line of this section is not entirely true; please see work from our laboratory exploring acute responses to a social media protocol and infuse these findings into your text here as this is not as novel of a topic with this citation included. https://hes32-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=https%3a%2f%2fpubmed.ncbi.nlm.nih.gov%2f28658082%2f&umid=2ba797c4-0763-42b4-9ef0-d2ada0e77048&auth=768f192bba830b801fed4f40fb360f4d1374fa7c-cc656fb46dcae2c1a350e96ae85fa406b896975c

We thank the reviewer for drawing attention to this previous work and have added reference to it in the introduction (line 52). However, although an important contribution to the literature we don’t feel this can be applied in the same context as the current study. Even though this study is based on a popular app, it is not a social media video (such as featured on YouTube), led by an unqualified social media influencer. Furthermore the paper compares this body weight protocol to a work matched protocol conducted on a cycle ergometer. This protocol (12x30s with 10s rest) has not previously been used within the literature (there is no evidence to show that it improves cardiorespiratory fitness). Therefore, we feel the statement “there is no research comparing the protocols used in these social media videos to those employed within the research.” is valid.

We agree and as outlined in the discussion believe that the different interval durations and work to rest ratios contribute significantly to the physiological and perceptual differences observed within the current study. We believe that future studies should continue to use the acute approach taken with the current study to investigate specifically how manipulating these different variables can influence physiological and perceptual outcomes, hopefully developing a protocol with high physiological load but also positive perceptual responses.

Line 179: Please confirm that this was a two-way ANOVA comparing differences in these variables across time as well as bout; thank you.

We agree this was previously unclear, a one-way within subject ANOVA was conducted to investigate heart rate responses, change in lactate, lowest reported feeling scale score and responses to the IMI questionnaire, as these are not pre to post values. This has been updated within the text for clarity (Line 217).

The incremental exercise test was used to calculate Wmax (PPO), this detail can be found on Line 116. More detailed information has been added to Line 110 indicating that all visits were completed at a similar time of day and all participants were asked to refrain from vigorous exercise 24 hours before and to fast 3hrs before completing the protocol.

Were any practice sessions allotted to the participants to improve their familiarity with these body weight exercises?

No all participants arrived to the lab without any prior knowledge of the exercise protocol/exercise they were going to perform. This information has been added to line 113 in the methods.

Were the instructions on how to interpret FS standardized and was the same experimenter tasked with recording this outcome in each session?

Instructions were standardised and same member of the experimental team provided the instruction. This detail has been added to Line 201.

I recommend that the Authors present some type of ES value in their Results to denote the meaningfulness of any differences—thank you.

Thank you for this recommendation, we have added effect size values to the results to signify meaningful difference and improve interpretation of the data by the reader. Details of the approach taken has been added to the statistical analysis section, line 222.

Results—line 199—is there a reason why predicted HRmax is used here when your baseline VO2max test allows you to actually assess true HRmax? Please clarify this.

Following the feedback from both reviewer 1 and yourself, we have now used the HRmax collected during the VO2max test. All results involving HR have now been updated to reflect a percentage of actual HRmax rather than predicted, and the appropriate statistical analysis has been recreated. Please see our response to reviewer one for further details.

Line 219—I believe this text needs some additional p values to better articulate the statistical results; thank you.

Due to the complexities of the protocols and the number of intervals included within each protocol, we feel the results section would not benefit from additional P values here. All significant P values have been indicated on Figure 3 for the reader.

Discussion—Lines 287-301 are nice but in my opinion, too replicative of the Introduction and in some ways, too speculative too. I think it would be best to condense some of this text and comment more on if the 20-10 bout (having the lowest interval duration and time > 80 %HRmax) is feasible and indicative of HIIE exercise vs. the other 3 regimens used. Also I believe that some of this text needs to be substituted by data from similarly habitually active participants rather than mice or trained cyclists, who have different exercise tolerance, BLa accumulation, etc. https://hes32-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=https%3a%2f%2fpubmed.ncbi.nlm.nih.gov%2f28737586%2f&umid=2ba797c4-0763-42b4-9ef0-d2ada0e77048&auth=768f192bba830b801fed4f40fb360f4d1374fa7c-583789331f56d08dc8e7493023e56163af122adf

We agree that this is an important distinction between the 4 protocols used within the current study. As such, we have added a short discussion of this point to lines 384-391 of the discussion. In short, our aim was not to investigate if the intensity regime influenced perceptual responses, and the design employed does not allow this, as different exercise modalities where used. However, previous research has shown that self-selected intensities results in more negative affect (using the FS) and, therefore, the intensity regime could have influenced the current data.

The manuscript is very well written, with a strong and balanced discussion including key studies in this field and highlighting opportunities for future research.

We appreciate the time the reviewer has dedicated to improve our manuscript and thank them for the feedback provided.

You may wish to consider the points below:

Methods:

More detail about the conditions in which the HIIT protocols were carried out have been added to the Methods section (Line 110-114).

In addition to the popularity of the YouTube clips, what considerations were made when choosing these two HIIT workouts?

We thank the reviewer for this suggestion. A new paragraph within the methods under the heading of ‘Training Protocols’ now provides greater insight into why the protocols were selected. In brief, we used 4 criteria to assess videos found on YouTube 1) had to be featured on a popular YouTube fitness channel 2) have ‘HIIT’ in the title of the video 3) take less than 20 minutes, to take advantage of the time-saving nature of HIIT 4) include body weight exercises with no equipment. From these videos the SM-20:10 protocol was included as the video uses “Tabata training”, a variation of the original protocol designed by Tabata et al. (1996) which has been demonstrated to increases in VO2peak. SM-40:20 was included as the protocol used a blend of aerobic and resistance-based exercises (e.g. press-ups) which would not typically fall under the traditional definition of HIIT, but is used by a number of videos found on social media channels.

Discussion:

We agree that the environment may have impacted the perceptual responses to the exercise protocols, this has now been added to the limitation sections. Equally the age of the participants is relevant to the responses seen as we agree social media protocols are aimed at a younger age group as a way to increase participation. This has been added to the limitation section (Line 433).

Limitations:

Participants being classified as recreationally active has been noted as a limitation of the study, however the sample size has not been mentioned.

The sample size has been added to the limitations, however to our knowledge this is one of the largest cross-over acute HIIT studies conducted.

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PLoS One. doi: 10.1371/journal.pone.0257685.r003

Decision Letter 1

Matthew M Schubert

8 Sep 2021

Evidence-based vs. social media based high-intensity interval training protocols: physiological and perceptual responses

PONE-D-21-08687R1

Dear Dr. Cocks,

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.

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Matthew M. Schubert, Ph.D.

Academic Editor

PLOS ONE

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Reviewer #2: All comments have been addressed

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

Reviewer #2: Yes

Reviewer #3: Yes

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

Reviewer #2: Yes

Reviewer #3: Yes

**********

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

Reviewer #2: Yes

Reviewer #3: Yes

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Reviewer #2: Yes

Reviewer #3: Yes

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6. Review Comments to the Author

Reviewer #2: I appreciate the revisions made by the Authors as well as the thorough rebuttal developed to my initial concerns--good luck with this line of work!

Reviewer #3: Thank you for addressing all comments thoroughly in your response letter; I have no further queries.

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PLoS One. doi: 10.1371/journal.pone.0257685.r004

Acceptance letter

Matthew M Schubert

21 Sep 2021

PONE-D-21-08687R1

Evidence-based vs. social media based high-intensity interval training protocols: physiological and perceptual responses

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PERMALINK

Evidence-based vs. social media based high-intensity interval training protocols: Physiological and perceptual responses

Katie L Hesketh

Hannah Church

Florence Kinnafick

Sam O Shepherd

Anton J M Wagenmakers

Matthew Cocks

Juliette A Strauss

Roles

Abstract

Objective

Methods

Results

Conclusions

Introduction

Methods

Participants

Study design

Initial experimental visit

Experimental visits

Training protocols

Ergometer laboratory based HIIT (Ergo-60:60)

Home-based body weight HIIT (BW-60:60)

Table 1. Summary of protocols used to measure acute responses to HIIT.

Social media HIIT 1 (SM-20:10)

Social media HIIT 2 (SM-40:20)

Assessment of heart rate during exercise

Perceptual responses during exercise

Feeling scale and felt arousal scale

Motivation

Intrinsic motivation inventory

Data analysis

Results

Physiological responses to exercise

Heart rate

Fig 1. Heart rate responses to the protocols.

Table 2. Heart rate (HR) responses to the HIIT protocols.

Blood Lactate

Fig 2. Change in lactate during the HIT protocols.

Perceptual responses during exercise

Feeling scale

Fig 3. Feeling scale (FS) responses to the protocols.

Circumplex model

Fig 4. Circumplex model to representing Feeling Scale (FS) and Felt Arousal Scale (FAS) responses to the protocols.

Motivational responses to exercise

Intrinsic motivation inventory

Fig 5. Intrinsic motivation inventory responses to the HIT protocols.

Discussion

Physiological responses to exercise

Perceptual responses to exercise

Motivation and enjoyment

Limitations

Conclusions

Data Availability

Funding Statement

References

Decision Letter 0

Kathryn L Weston

Roles

Author response to Decision Letter 0

Decision Letter 1

Matthew M Schubert

Roles

Acceptance letter

Matthew M Schubert

Roles

Associated Data

Supplementary Materials

Data Availability Statement

ACTIONS

PERMALINK

RESOURCES

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