Is low-volume high-intensity interval training a time-efficient strategy to improve cardiometabolic health and body composition? A meta-analysis.

The present meta-analysis aimed to assess the effects of low-volume high-intensity interval training (LV-HIIT; i.e., ≤5 min high-intensity exercise within a ≤15 min session) on cardiometabolic health and body composition. A systematic search was performed in accordance with PRISMA guidelines to assess the effect of LV-HIIT on cardiometabolic health and body composition. Twenty-one studies (moderate to high quality) with a total of 849 participants were included in this meta-analysis. LV-HIIT increased cardiorespiratory fitness (CRF, SMD = 1.19 [0.87, 1.50]) while lowering systolic blood pressure (SMD = -1.44 [-1.68, -1.20]), diastolic blood pressure (SMD = -1.51 [-1.75, -1.27]), mean arterial pressure (SMD = -1.55 [-1.80, -1.30]), MetS z-score (SMD = -0.76 [-1.02, -0.49]), fat mass (kg) (SMD = -0.22 [-0.44, 0.00]), fat mass (%) (SMD = -0.22 [-0.41, -0.02]), and waist circumference (SMD = -0.53 [-0.75, -0.31]) compared to untrained control (CONTROL). Despite a total time-commitment of LV-HIIT of only 14%-47% and 45%-94% compared to moderate-intensity continuous training and HV-HIIT, respectively, there were no statistically significant differences observed for any outcomes in comparisons between LV-HIIT and moderate-intensity continuous training (MICT) or high-volume HIIT. Significant inverse dose-responses were observed between the change in CRF with LV-HIIT and sprint repetitions (ß = -0.52 [-0.76, -0.28]), high-intensity duration (ß = -0.21 [-0.39, -0.02]), and total duration (ß = -0.19 [-0.36, -0.02]), while higher intensity significantly improved CRF gains. LV-HIIT can improve cardiometabolic health and body composition and represent a time-efficient alternative to MICT and HV-HIIT. Performing LV-HIIT at a higher intensity drives higher CRF gains. More repetitions, longer time at high intensity, and total session duration did not augment gains in CRF.

Exploring interindividual differences in fasting and postprandial insulin sensitivity adaptations in response to sprint interval exercise training.

Previous studies have concluded that wide variance in changes in insulin sensitivity markers following exercise training demonstrates heterogeneity in individual trainability. However, these studies frequently don't account for technical, biological, and random within-subject measurement error. We used the standard deviation of individual responses (SDIR) to determine whether interindividual variability in trainability exists for fasting and postprandial insulin sensitivity outcomes following low-volume sprint interval training (SIT). We pooled data from 63 untrained participants who completed 6 weeks of SIT (n = 49; VO2max: 35 (7) mL⋅kg-1⋅min-1) or acted as no-intervention controls (n = 14; VO2max: 34 (6) mL⋅kg-1⋅min-1). Fasting and oral glucose tolerance test (OGTT)-derived measures of insulin sensitivity were measured pre- and post-intervention. SDIR values were positive and exceeded a small effect size threshold for changes in fasting glucose (SDIR = 0.27 [95%CI 0.07,0.38] mmol⋅L-1), 2-h OGTT glucose (SDIR = 0.89 [0.22,1.23] mmol⋅L-1), glucose area-under-the-curve (SDIR = 66.4 [-81.5,124.3] mmol⋅L-1⋅120min-1) and The Cederholm Index (SDIR = 7.2 [-16.0,19.0] mg⋅l2⋅mmol-1⋅mU-1⋅min-1), suggesting meaningful individual responses to SIT, whilst SDIR values were negative for fasting insulin, fasting insulin resistance and insulin AUC. For all variables, the 95% CIs were wide and/or crossed zero, highlighting uncertainty about the existence of true interindividual differences in exercise trainability. Only 2-22% of participants could be classified as responders or non-responders with more than 95% certainty. Our findings demonstrate it cannot be assumed that variation in changes in insulin sensitivity following SIT is attributable to inherent differences in trainability, and reiterate the importance of accounting for technical, biological, and random error when examining heterogeneity in health-related training adaptations.Highlights This study tested whether true interindividual variability exists for changes in insulin sensitivity and glyceamic control following 6-weeks of low volume sprint interval training (SIT).The high level of technical, biological, and random error associated with repeated measurements of insulin sensitivity and glycaemic control, means we can neither confidently conclude that there is evidence of true interindividual differences in the trainability of these outcomes following SIT, nor confidently identify responders or non-responders for such parameters.Researchers contrasting responders vs. non-responders for a given parameter, either to understand mechanisms of adaptation and/or develop physiological/genetic/epigenetic predictors of response, need to be aware that identification of responders and non-responders with sufficient certainty may not be achievable for parameters with a high level of technical, biological, and random error.

Affecting Effects on Affect: The Impact of Protocol Permutations on Affective Responses to Sprint Interval Exercise; A Systematic Review and Meta-Analysis of Pooled Individual Participant Data.

Responses to sprint interval exercise (SIE) are hypothesized to be perceived as unpleasant, but SIE protocols are diverse, and moderating effects of various SIE protocol parameters on affective responses are unknown. We performed a systematic search to identify studies (up to 01/05/2021) measuring affective valence using the Feeling Scale during acute SIE in healthy adults. Thirteen studies involving 18 unique trials and 316 unique participant (142 women and 174 men) affective responses to SIE were eligible for inclusion. We received individual participant data for all participants from all studies. All available end-of-sprint affect scores from each trial were combined in a linear mixed model with sprint duration, mode, intensity, recovery duration, familiarization and baseline affect included as covariates. Affective valence decreased significantly and proportionally with each additional sprint repetition, but this effect was modified by sprint duration: affect decreased more during 30 s (0.84 units/sprint; 95% CI: 0.74-0.93) and 15-20 s sprints (1.02 units/sprint; 95% CI: 0.93-1.10) compared with 5-6 s sprints (0.20 units/sprint; 95% CI: 0.18-0.22) (both p < 0.0001). Although the difference between 15-20 s and 30 s sprints was also significant (p = 0.02), the effect size was trivial (d = -0.12). We observed significant but trivial effects of mode, sprint intensity and pre-trial familiarization, whilst there was no significant effect of recovery duration. We conclude that affective valence declines during SIE, but the magnitude of the decrease for an overall SIE session strongly depends on the number and duration of sprints. This information can be applied by researchers to design SIE protocols that are less likely to be perceived as unpleasant in studies of real-world effectiveness. SYSTEMATIC REVIEW REGISTRATION: Open Science Framework, https://osf.io/sbyn3.

The effect of mouth rinsing with different concentrations of caffeine solutions on reaction time.

Caffeine mouth rinsing (CAF-MR) has been shown to improve reaction time (RT). CAF-MR studies have generally used 1.2% CAF concentrations, but the effect of using different concentrations is unknown. Therefore, we compared the effect of different concentrations of CAF-MR on RT. Forty-five trained male athletes (age: 18 ± 3 y) volunteered to participate in this double-blind, randomized controlled crossover study. Participants completed five testing sessions (Control, Placebo (water)-MR, and 1.2%, 1.8%, and 2.4% CAF-MR), with hand and foot RTs assessed immediately after MR. All CAF-MR conditions resulted in significantly faster hand and foot RT compared to Control and Placebo (all p < 0.001, except for foot RT with 1.8% CAF-MR vs. Placebo: NS). For both hand and foot RT, 1.2% and 1.8% CAF-MR did not significantly differ, but RT for 2.4% CAF-MR was significantly faster than both (p < 0.001). Improvements in RT for 2.4% CAF-MR vs. Placebo were 22% for hand RT and 21% for foot RT. In conclusion, these findings demonstrate that higher CAF-MR concentrations than those typically used can result in greater improvements in RT. This has implications for the practical use of CAF-MR to enhance performance in sports in which optimal RT is a factor of success.

Improvements in Maximal Oxygen Uptake After Sprint-Interval Training Coincide with Increases in Central Hemodynamic Factors.

INTRODUCTION: Sprint-interval training has been shown to improve maximal oxygen uptake, in part through peripheral muscle adaptations that increase oxygen utilization. In contrast, the adaptations of central hemodynamic factors in this context remain unexplored. PURPOSE: The aim of the current study was to explore the effects of sprint-interval training on maximal oxygen uptake and central hemodynamic factors. METHODS: Healthy men and women (n = 29; mean age, 27 ± 5 yr; height, 175 ± 8 cm; body mass, 72.5 ± 12.0 kg) performed 6 wk of sprint-interval training consisting of three weekly sessions of 10-min low-intensity cycling interspersed with 3 × 30-s all-out sprints. Maximal oxygen uptake, total blood volume, and maximal cardiac output were measured before and after the intervention. RESULTS: Maximal oxygen uptake increased by 10.3% (P < 0.001). Simultaneously, plasma volume, blood volume, total hemoglobin mass, and cardiac output increased by 8.1% (276 ± 234 mL; P < 0.001), 6.8% (382 ± 325 mL; P < 0.001), 5.7% (42 ± 41 g; P < 0.001), and 8.5% (1.0 ± 0.9 L·min-1; P < 0.001), respectively. Increased total hemoglobin mass along with measures of body surface area had a significant impact on the improvements in maximal oxygen uptake. CONCLUSIONS: Six weeks of sprint-interval training results in significant increases in hemoglobin mass, blood volume, and cardiac output. Because these changes were associated with marked improvements in maximal oxygen uptake, we conclude that central hemodynamic adaptations contribute to the improvement in maximal oxygen uptake during sprint-interval training.

Heterogeneity and incidence of non-response for changes in cardiorespiratory fitness following time-efficient sprint interval exercise training.

Interindividual variability for training-induced changes in maximal oxygen uptake (V̇O2max) is well described following continuous aerobic and high-intensity interval training. Whether similar variability is observed following time-efficient sprint interval training with minimal training volume (i.e., reduced-exertion high-intensity interval training; REHIT) is unknown. We conducted a pooled analysis of n = 117 (68 men) training participants (mean ± SD: age: 30 ± 10 y; V̇O2max: 34.8 ± 7.5 mL·kg-1·min-1), who completed a V̇O2max assessment before and 3 days after 6 weeks of REHIT comprising of two 10-20-s 'all-out' cycling sprints per session, and n = 40 no-intervention control participants (age: 30 ± 13 y; V̇O2max: 31.5 ± 6.5 mL·kg-1·min-1) who completed repeated V̇O2max tests over a comparable timeframe. Individual responses estimated using 50% confidence intervals derived from the technical error were interpreted against a smallest worthwhile change of 1.75 mL·kg-1·min-1. The standard deviation of individual responses was 2.39 mL·kg-1·min-1 demonstrating clinically meaningful heterogeneity in training-induced changes in V̇O2max following REHIT that exceed the technical, biological and random within-subjects variability of V̇O2max assessment. The likely (75% probability) non-response rate was 18% (21/117), and 49% (57/117) of individuals demonstrated increases in V̇O2max likely higher than the smallest worthwhile change. We conclude that the well-described increase in V̇O2max following REHIT at the group level is subject to substantial variability in magnitude at an individual level. This has important implications for exercise prescription and can be harnessed to elucidate mechanisms of adaptation. Novelty: There is substantial heterogeneity in V̇O2max responses following time-efficient sprint interval training. Proportion of non-response was 18% and ∽50% of individuals show clinically meaningful increases in V̇O2max.

Time-efficient and computer-guided sprint interval exercise training for improving health in the workplace: a randomised mixed-methods feasibility study in office-based employees.

BACKGROUND: The efficacy of high-intensity interval training (HIT) as a time-efficient exercise strategy for beneficially modifying risk factors for cardiovascular disease has repeatedly been demonstrated in controlled laboratory settings. However, the effectiveness of HIT in an unsupervised workplace setting has not been investigated. The objective of this study was to use mixed methods to investigate the feasibility, acceptability and effectiveness of a short-duration, high-intensity exercise intervention (REHIT) when applied unsupervised in a workplace setting. METHODS: Twenty-five office-workers (mean ± SD age: 47 ± 9 y, BMI: 27.5 ± 4.4 kg·m- 2, V̇O2max: 28 ± 7 mL·kg- 1·min- 1) completed a 6-week REHIT intervention unsupervised in their workplace (n = 13, 6 men), or acted as a no-intervention control (n = 12, 6 men). The intervention consisted of 2 sessions/week of low-intensity (~ 25 W) cycling interspersed with 2 'all-out' sprints, increasing in duration from 10 to 20 s per sprint over the 6 weeks (total time-commitment: 8:40 min per session). V̇O2max was assessed pre- and post-training, whilst questionnaire-based measures of exercise enjoyment, self-efficacy, and acceptability were completed post-training. Eight participants also completed post-intervention semi-structured interviews. RESULTS: V̇O2max significantly improved in the exercise group (2.25 ± 0.75 L·min- 1 vs. 2.42 ± 0.82 L·min- 1; + 7.4%) compared to the control group (2.22 ± 0.72 L·min- 1 vs. 2.17 ± 0.74 L·min- 1; - 2.3%; time*intervention interaction effect: p < 0.01). Participants considered the REHIT intervention acceptable and enjoyable (PACES: 89 ± 17 out of 119) and were confident in their ability to continue to perform REHIT (7.8 ± 1.2 out of 9). Qualitative data revealed that REHIT offered a time-efficient opportunity to exercise, that was perceived as achievable, and which encouraged highly valued post-exercise outcomes (e.g. progress towards health/fitness benefits). CONCLUSIONS: REHIT could be implemented as a feasible, effective and acceptable exercise intervention in a workplace setting, with a total time-commitment of < 20 min/week. Consideration of certain psycho-social factors and behaviour-change techniques may ensure adherence to the REHIT programme in the long term. TRIAL REGISTRATION: The study was registered on ClinicalTrials.gov on 07/05/2019 (registration: NCT03941145).

Reducing training frequency from 3 or 4 sessions/week to 2 sessions/week does not attenuate improvements in maximal aerobic capacity with reduced-exertion high-intensity interval training (REHIT).

In the present randomised-controlled trial we investigated the effect of reduced-exertion high-intensity interval training (REHIT) training frequency (2, 3, or 4 sessions/week for 6 weeks) on maximal aerobic capacity in 42 inactive individuals (13 women; mean ± SD age: 25 ± 5 years, maximal aerobic capacity: 35 ± 5 mL·kg-1·min-1). Changes in maximal aerobic capacity were not significantly different between the 3 groups (2 sessions/week: +10.2%; 3 sessions/week: +8.1%; 4 sessions per week: +7.3%). In conclusion, a training frequency of 2 sessions/week is sufficient for REHIT to improve maximal aerobic capacity. Novelty We demonstrate that reducing REHIT training frequency from 3 or 4 to 2 sessions/week does not attenuate improvements in the key health marker of maximal aerobic capacity.

Evaluating differences in the clinical impact of a free online weight loss programme, a resource-intensive commercial weight loss programme and an active control condition: a parallel randomised controlled trial.

BACKGROUND: Finding effective intervention strategies to combat rising obesity levels could significantly reduce the burden that obesity and associated non-communicable diseases places on both individuals and the National Health Service. METHODS: In this parallel randomised-controlled trial, 76 participants who are overweight or obese (50 female) were given free access to a fitness centre for the duration of the 12-week intervention and randomised to one of three interventions. The commercial intervention, the Healthy Weight Programme, (HWP, n = 25, 10/15 men/women) consisted of twelve 1-h nutrition coaching sessions with a nutritionist delivered as a mixture of group and 1 to 1 sessions. In addition, twice-weekly exercise sessions (24 in total) were delivered by personal trainers for 12 weeks. The NHS intervention (n = 25, 8/17 men/women) consisted of following an entirely self-managed 12-week online NHS resource. The GYM intervention (n = 26, 8/18 men/women) received no guidance or formal intervention. All participants were provided with a gym induction for safety and both the NHS and GYM participants were familiarised with ACSM physical activity guidelines by way of a hand-out. RESULTS: The overall follow-up rate was 83%. Body mass was significantly reduced at post-intervention in all groups (HWP: N = 18, - 5.17 ± 4.22 kg, NHS: N = 21-4.19 ± 5.49 kg; GYM: N = 24-1.17 ± 3.00 kg; p < 0.001) with greater reductions observed in HWP and NHS groups compared to GYM (p < 0.05). Out with body mass and BMI, there were no additional statistically significant time x intervention interaction effects. CONCLUSIONS: This is the first study to evaluate the efficacy of both a free online NHS self-help weight-loss tool and a commercial weight loss programme that provides face-to-face nutritional support and supervised exercise. The findings suggest that both interventions are superior to an active control condition with regard to eliciting short-term weight-loss. TRIAL REGISTRATION: ISRCTN Registry - ISRCTN31489026. Prospectively registered: 27/07/16.

Effects of a Novel Neurodynamic Tension Technique on Muscle Extensibility and Stretch Tolerance: A Counterbalanced Crossover Study.

CONTEXT: Neurodynamic tension affects hamstring extensibility and stretch tolerance and is considered important in hamstring injury management. Neurodynamic tension was postulated to affect segmental muscle extensibility and stretch tolerance and potentially also to demonstrate extrasegmental and contralateral effects. OBJECTIVES: To assess the effects of a novel sciatic-tibial neurodynamic tension technique, the modified long sit slump (MLSS), on segmental, extrasegmental, and contralateral muscle extensibility and stretch tolerance. STUDY DESIGN: Counterbalanced crossover study. SETTING: University research laboratory. PARTICIPANTS: 13 healthy and active subjects (mean ± SD age 24 ± 8 y; BMI, 23.1 ± 2.8 kg/m2). INTERVENTION: MLSS application (5 s, 5 repetitions, 3 sets) on 2 occasions with a 3-wk washout period, and either stance- or skill-leg treated in a counterbalanced manner. MAIN OUTCOME MEASURES: Segmental and extrasegmental muscle extensibility was measured using passive straight-leg raise (PSLR) and prone knee bend (PKB) at pre-, immediately post-, and 1 h postintervention. Stretch-intensity ratings were measured using a simple numerical rating scale (SNRS). RESULTS: MLSS significantly increased PSLR and PKB bilaterally (P < .001). The effect for PSLR was greater in the ipsilateral leg compared to the contralateral leg (baseline to 1 h post: +9° ± 6° and +5° ± 5°, respectively, P < .001) but not for PKB (baseline to 1 h post: ipsilateral leg +5° ± 5°, contralateral leg +5° ± 4°). For both PSLR and PKB the effect of the first session was retained at the start of the second session 3 wk later. SNRS data were consistent with increased stretch tolerance. CONCLUSIONS: Application of a novel sciatic-tibial neurodynamic tension technique, the MLSS, increases muscle extensibility and stretch tolerance segmentally, extrasegmentally and contralaterally. LEVEL OF EVIDENCE: 2C outcomes research.

Decreasing sprint duration from 20 to 10 s during reduced-exertion high-intensity interval training (REHIT) attenuates the increase in maximal aerobic capacity but has no effect on affective and perceptual responses.

Recent studies have demonstrated that modifying the "classic" 6 × 30-s "all-out" sprint interval training protocol by incorporating either shorter sprints (6 × 10-s or 15-s sprints) or fewer sprints (e.g., 2 × 20-s sprints; reduced-exertion high-intensity interval training (REHIT)) does not attenuate the training-induced improvements in maximal aerobic capacity. The aim of the present study was to determine if reducing the sprint duration in the REHIT protocol from 20 s to 10 s per sprint influences acute affective responses and the change in maximal aerobic capacity following training. Thirty-six sedentary or recreationally active participants (17 women; mean ± SD; age: 22 ± 3 years; body mass index: 24.5 ± 4.6 kg·m-2; maximal aerobic capacity: 37 ± 8 mL·kg-1·min-1) were randomised to a group performing a "standard" REHIT protocol involving 2 × 20-s sprints or a group who performed 2 × 10-s sprints. Maximal aerobic capacity was determined before and after 6 weeks of 3 weekly training sessions. Acute affective responses and perceived exertion were assessed during training. Greater increases in maximal aerobic capacity were observed for the group performing 20-s sprints (2.77 ± 0.75 to 3.04 ± 0.75 L·min-1; +10%) compared with the group performing 10-s sprints (2.58 ± 0.57 vs. 2.67 ± 3.04 L·min-1; +4%; group × time interaction effect: p < 0.05; d = 1.06). Positive affect and the mood state vigour increased postexercise, while tension, depression, and total mood disturbance decreased, and negative affect remained unchanged. Affective responses and perceived exertion were not altered by training and were not different between groups. In conclusion, reducing sprint duration in the REHIT protocol from 20 s to 10 s attenuates improvements in maximal aerobic capacity, and does not result in more positive affective responses or lower perceived exertion.

A Practical and Time-Efficient High-Intensity Interval Training Program Modifies Cardio-Metabolic Risk Factors in Adults with Risk Factors for Type II Diabetes.

INTRODUCTION: Regular physical activity (PA) can reduce the risk of developing type 2 diabetes, but adherence to time-orientated (150 min week-1 or more) PA guidelines is very poor. A practical and time-efficient PA regime that was equally efficacious at controlling risk factors for cardio-metabolic disease is one solution to this problem. Herein, we evaluate a new time-efficient and genuinely practical high-intensity interval training (HIT) protocol in men and women with pre-existing risk factors for type 2 diabetes. MATERIALS AND METHODS: One hundred eighty-nine sedentary women (n = 101) and men (n = 88) with impaired glucose tolerance and/or a body mass index >27 kg m-2 [mean (range) age: 36 (18-53) years] participated in this multi-center study. Each completed a fully supervised 6-week HIT protocol at work-loads equivalent to ~100 or ~125% [Formula: see text]. Change in [Formula: see text] was used to monitor protocol efficacy, while Actiheart™ monitors were used to determine PA during four, weeklong, periods. Mean arterial (blood) pressure (MAP) and fasting insulin resistance [homeostatic model assessment (HOMA)-IR] represent key health biomarker outcomes. RESULTS: The higher intensity bouts (~125% [Formula: see text]) used during a 5-by-1 min HIT protocol resulted in a robust increase in [Formula: see text] (136 participants, +10.0%, p < 0.001; large size effect). 5-by-1 HIT reduced MAP (~3%; p < 0.001) and HOMA-IR (~16%; p < 0.01). Physiological responses were similar in men and women while a sizeable proportion of the training-induced changes in [Formula: see text], MAP, and HOMA-IR was retained 3 weeks after cessation of training. The supervised HIT sessions accounted for the entire quantifiable increase in PA, and this equated to 400 metabolic equivalent (MET) min week-1. Meta-analysis indicated that 5-by-1 HIT matched the efficacy and variability of a time-consuming 30-week PA program on [Formula: see text], MAP, and HOMA-IR. CONCLUSION: With a total time-commitment of <15 min per session and reliance on a practical ergometer protocol, 5-by-1 HIT offers a new solution to modulate cardio-metabolic risk factors in adults with pre-existing risk factors for type 2 diabetes while approximately meeting the MET min week-1 PA guidelines. Long-term randomized controlled studies will be required to quantify the ability for 5-by-1 HIT to reduce the incidence of type 2 diabetes, while strategies are required to harmonize the adaptations to exercise across individuals.

Research into the Health Benefits of Sprint Interval Training Should Focus on Protocols with Fewer and Shorter Sprints.

Over the past decade, it has been convincingly shown that regularly performing repeated brief supramaximal cycle sprints (sprint interval training [SIT]) is associated with aerobic adaptations and health benefits similar to or greater than with moderate-intensity continuous training (MICT). SIT is often promoted as a time-efficient exercise strategy, but the most commonly studied SIT protocol (4-6 repeated 30-s Wingate sprints with 4 min recovery, here referred to as 'classic' SIT) takes up to approximately 30 min per session. Combined with high associated perceived exertion, this makes classic SIT unsuitable as an alternative/adjunct to current exercise recommendations involving MICT. However, there are no indications that the design of the classic SIT protocol has been based on considerations regarding the lowest number or shortest duration of sprints to optimise time efficiency while retaining the associated health benefits. In recent years, studies have shown that novel SIT protocols with both fewer and shorter sprints are efficacious at improving important risk factors of noncommunicable diseases in sedentary individuals, and provide health benefits that are no worse than those associated with classic SIT. These shorter/easier protocols have the potential to remove many of the common barriers to exercise in the general population. Thus, based on the evidence summarised in this current opinion paper, we propose that there is a need for a fundamental change in focus in SIT research in order to move away from further characterising the classic SIT protocol and towards establishing acceptable and effective protocols that involve minimal sprint durations and repetitions.

A comparison of the health benefits of reduced-exertion high-intensity interval training (REHIT) and moderate-intensity walking in type 2 diabetes patients.

Reduced-exertion high-intensity interval training (REHIT) is a genuinely time-efficient intervention that can improve aerobic capacity and insulin sensitivity in sedentary individuals. The present study compared the effects of REHIT and moderate-intensity walking on health markers in patients with type 2 diabetes (T2D) in a counter-balanced crossover study. Sixteen men with T2D (mean ± SD age: 55 ± 5 years, body mass index: 30.6 ± 2.8 kg·m-2, maximal aerobic capacity: 27 ± 4 mL·kg-1·min-1) completed 8 weeks of REHIT (three 10-min low-intensity cycling sessions/week with two "all-out" 10-20-s sprints) and 8 weeks of moderate-intensity walking (five 30-min sessions/week at an intensity corresponding to 40%-55% of heart-rate reserve), with a 2-month wash-out period between interventions. Before and after each intervention, participants underwent an incremental fitness test, an oral glucose tolerance test (OGTT), a whole-body dual-energy X-ray absorptiometry scan, and continuous glucose monitoring. REHIT was associated with a significantly larger increase in maximal aerobic capacity compared with walking (7% vs. 1%; time × intervention interaction effect: p < 0.05). Both REHIT and walking decreased resting mean arterial pressure (-4%; main effect of time: p < 0.05) and plasma fructosamine (-5%; main effect of time: p < 0.05). Neither intervention significantly improved OGTT-derived measures of insulin sensitivity, glycaemic control measured using continuous glucose monitors, blood lipid profile, or body composition. We conclude that REHIT is superior to a 5-fold larger volume of moderate-intensity walking in improving aerobic fitness, but similar to walking REHIT is not an effective intervention for improving insulin sensitivity or glycaemic control in T2D patients in the short term.

Effect of Number of Sprints in an SIT Session on Change in V˙O2max: A Meta-analysis.

PURPOSE: Recent meta-analyses indicate that sprint interval training (SIT) improves cardiorespiratory fitness (V˙O2max), but the effects of various training parameters on the magnitude of the improvement remain unknown. The present meta-analysis examined the modifying effect of the number of sprint repetitions in an SIT session on improvements in V˙O2max. METHODS: The databases PubMed and Web of Science were searched for original studies that have examined pre- and posttraining V˙O2max in adults after ≥2 wk of training consisting of repeated (≥2) Wingate-type cycle sprints, published up to May 1, 2016. Articles were excluded if they were not in English; if they involved patients, athletes, or participants with a mean baseline V˙O2max of >55 mL·kg·min or a mean age <18 yr; and if an SIT trial was combined with another intervention or used intervals shorter than 10 s. A total of 38 SIT trials from 34 studies were included in the meta-analysis. Probabilistic magnitude-based inferences were made to interpret the outcome of the analysis. RESULTS: The meta-analysis revealed a likely large effect of a typical SIT intervention on V˙O2max (mean ± 90% confidence limits = 7.8% ± 4.0%) with a possibly small modifying effect of the maximum number of sprint repetitions in a training session (-1.2% ± 0.8% decrease per two additional sprint repetitions). Apart from possibly small effects of baseline V˙O2max and age, all other modifying effects were unclear or trivial. CONCLUSION: We conclude that the improvement in V˙O2max with SIT is not attenuated with fewer sprint repetitions, and possibly even enhanced. This means that SIT protocols can be made more time efficient, which may help SIT to be developed into a viable strategy to impact public health.

No effect of acute and chronic supramaximal exercise on circulating levels of the myokine SPARC.

Myokines may play a role in the health benefits of regular physical activity. Secreted protein acidic rich in cysteine (SPARC) is a pleiotropic myokine that has been shown to be released into the bloodstream by skeletal muscle in response to aerobic exercise. As there is evidence suggesting that SPARC release may be linked to glycogen breakdown and activation of 5' adenosine monophosphate-activated protein kinase, we hypothesised that brief supramaximal exercise may also be associated with increased serum SPARC levels. In the present study, 10 participants (3 women; mean ± SD age: 21 ± 3 y, body mass index (BMI): 22 ± 3 kg m-2, and V˙O2max: 39 ± 6 mL kg-1 min-1) performed an acute bout of supramaximal cycle exercise (20-s Wingate sprint against 7.5% of body mass, with a 1-min warm-up and a 3-min cool-down consisting of unloaded cycling). Serum SPARC levels were determined pre-exercise as well as 0, 15, and 60 min post-exercise and corrected for plasma volume change. To determine whether regular exercise affected the acute SPARC response, participants repeated the acute exercise protocol three times per week for four weeks, and serum SPARC response to supramaximal exercise was reassessed after this period. Acute supramaximal exercise significantly decreased plasma volume (-10%; p < .001), but was not associated with a significant change in serum SPARC levels at either the pre-training or post-training testing sessions. In conclusion, in contrast to aerobic exercise, a single brief supramaximal cycle sprint is not associated with an increase in serum SPARC levels, suggesting that SPARC release is not related to skeletal muscle glycogen breakdown.