Sprint Interval Exercise Training Research Articles

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

ABSTRACT 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.

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 (VO2max) 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; VO2max: 34.8±7.5 ml·kg-1·min-1), who completed a VO2max assessment before and 3 days after 6 weeks of REHIT comprising of two 10-20 second 'all-out' cycling sprints per session, and n=40 no-intervention control participants (age: 30±13 y; VO2max: 31.5±6.5 ml·kg-1·min-1) who completed repeated VO2max tests over a comparable timeframe. Individual responses estimated using 50% confidence intervals derived from the technical error were interpreted against a smallest worthwhile change (SWC) 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 VO2max following REHIT that exceed the technical, biological and random within-subjects variability of VO2max assessment. The likely (75% probability) non-response rate was 18% (21/117), and 49% (57/117) of individuals demonstrated increases in VO2max likely higher than the SWC. We conclude that the well-described increase in VO2max 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 VO2max responses following time-efficient sprint interval training • Proportion of non-response was 18% and ∽50% of individuals show clinically meaningful increases in VO2max.

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

BackgroundThe 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.MethodsTwenty-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.ResultsV̇O2max 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).ConclusionsREHIT 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 registrationThe study was registered on ClinicalTrials.gov on 07/05/2019 (registration: NCT03941145).

Effects of sprint interval training on ectopic lipids and tissue-specific insulin sensitivity in men with non-alcoholic fatty liver disease.

This study examined the feasibility of sprint interval exercise training (SIT) for men with non-alcoholic fatty liver disease (NAFLD) and its effects on intrahepatic triglyceride (IHTG), insulin sensitivity (hepatic and peripheral), visceral (VAT) and subcutaneous adipose tissue (ScAT). Nine men with NAFLD (age 41 ± 8years; BMI 31.7 ± 3.1 kgm-2; IHTG 15.6 ± 8.3%) were assessed at: (1) baseline (2) after a control phase of no intervention (pre-training) and (3) after 6weeks of SIT (4-6 maximal 30s cycling intervals, three times per week). IHTG, VAT and ScAT were measured using magnetic resonance spectroscopy or imaging and insulin sensitivity was assessed via dual-step hyperinsulinaemic-euglycaemic clamp with [6,6-D2] glucose tracer. Participants adhered to SIT, completing ≥ 96.7% of prescribed intervals. SIT increased peak oxygen uptake [[Formula: see text] peak: +13.6% (95% CI 8.8-18.2%)] and elicited a relative reduction in IHTG [-12.4% (-31.6 to 6.7%)] and VAT [-16.9% (-24.4 to -9.4%); n = 8], with no change in body weight or ScAT. Peripheral insulin sensitivity increased throughout the study (n = 8; significant main effect of phase) but changes from pre- to post-training were highly variable (range -18.5 to +58.7%) and not significant (P = 0.09), despite a moderate effect size (g*=0.63). Hepatic insulin sensitivity was not influenced by SIT. SIT is feasible for men with NAFLD in a controlled laboratory setting and is able to reduce IHTG and VAT in the absence of weight loss.

FRI-350 - Sprint interval exercise training reduces intrahepatic, visceral and subcutaneous abdominal fat despite no change in body weight, but has variable effects on whole-body insulin sensitivity

FRI-350 - Sprint interval exercise training reduces intrahepatic, visceral and subcutaneous abdominal fat despite no change in body weight, but has variable effects on whole-body insulin sensitivity

Circulating protein synthesis rates reveal skeletal muscle proteome dynamics.

Here, we have described and validated a strategy for monitoring skeletal muscle protein synthesis rates in rodents and humans over days or weeks from blood samples. We based this approach on label incorporation into proteins that are synthesized specifically in skeletal muscle and escape into the circulation. Heavy water labeling combined with sensitive tandem mass spectrometric analysis allowed integrated synthesis rates of proteins in muscle tissue across the proteome to be measured over several weeks. Fractional synthesis rate (FSR) of plasma creatine kinase M-type (CK-M) and carbonic anhydrase 3 (CA-3) in the blood, more than 90% of which is derived from skeletal muscle, correlated closely with FSR of CK-M, CA-3, and other proteins of various ontologies in skeletal muscle tissue in both rodents and humans. Protein synthesis rates across the muscle proteome generally changed in a coordinate manner in response to a sprint interval exercise training regimen in humans and to denervation or clenbuterol treatment in rodents. FSR of plasma CK-M and CA-3 revealed changes and interindividual differences in muscle tissue proteome dynamics. In human subjects, sprint interval training primarily stimulated synthesis of structural and glycolytic proteins. Together, our results indicate that this approach provides a virtual biopsy, sensitively revealing individualized changes in proteome-wide synthesis rates in skeletal muscle without a muscle biopsy. Accordingly, this approach has potential applications for the diagnosis, management, and treatment of muscle disorders.

Short and sweet: cardiovascular and metabolic improvements in just one hour per week.

Short and sweet: cardiovascular and metabolic improvements in just one hour per week.

B-33 Free Communication/Poster - Heat Stress

The fat loss associated with sprint interval exercise training (SIT; 3 sessions/wk over 6 wk) cannot be explained fully by an increased 24-h energy expenditure associated with this type of training (Hazell et al 2012). Rather, a cumulative effect of reduced energy intake (EI), increased post-exercise oxygen consumption (VO2), and/or increased lipid oxidation may explain this outcome. PURPOSE: To assess the effects of acute sprint interval exercise (SIE) on EI, subjective appetite, appetite-related peptides, VO2, and whole-body substrate oxidation (RER). METHODS: Eight men (25±3 y, 79.6±9.7 kg, body fat 13±6%; mean±SD) completed two, systematically rotated 34-h treatments consisting of consecutive 10-h test days: SIE and recovery (SIEx) and no exercise control (NoEx). Between 0800-1800 h, participants remained in the laboratory for 8 breath-by-breath gas collections, 3 ad libitum buffet-type meals, 14 ratings of hunger, fullness, satiety and motivation to eat, and 4 blood samples for GLP-1, insulin, pancreatic polypeptide, and PYY. At 1800 h, participants went home with a snack bag, remained sedentary, and returned the following morning for the second test day. Area under the curve (AUC) for total (34-h) VO2 and appetite ratings was calculated with the trapezoid method. Treatment comparisons were made using two-way repeated measures ANOVA (treatment × time) or t-tests. RESULTS: Immediate, albeit short-lived (<1 h), post-exercise suppression of appetite and increase in PYY were observed during SIEx (p<0.001). However, AUC for hunger and motivation to eat were greater during SIEx (p<0.02), but this did not affect 34-h EI (SIEx: 24.6±4.8 vs NoEx: 24.9±5.4 MJ; p=0.76). RER was lower ∼6 h post-exercise (p<0.001) and total VO2 was greater during SIEx (560±88 L) vs NoEx (491±107 L; p=0.05). CONCLUSIONS: Acute SIE suppresses appetite briefly, but subsequently results in greater feelings of hunger and motivation to eat. Despite its effects on appetite and PYY, SIE did not affect 34-h EI. Therefore, following acute SIE, energy expenditure is increased but EI remains the same, suggesting that increases in energy expenditure and alterations in lipid oxidation likely explain the fat loss associated with this training modality. Supported by Gatorade Sport Science Institute, Subway, PepsiCo and Real Canadian Superstore.

Effect of acute sprint interval exercise on central and peripheral artery distensibility in young healthy males

Peripheral arterial distensibility is improved with sprint interval exercise training in young healthy participants (Rakobowchuk et al. in Am J Physiol Regul Integr Comp Physiol 295:R236-R242, 2008). To fully understand the mechanisms contributing to these training effects it is useful to examine the acute responses to sprint interval exercise. Following supine rest, nine healthy males completed either a single sprint interval (Wingate test) or a multiple sprint interval exercise session (4 Wingate tests each separated by 4.5 min). Following exercise, participants recovered for 60 min while central and peripheral arterial distensibility measurements were conducted at discrete time points, using applanation tonometry and ultrasound imaging and continuously, using central and peripheral pulsewave velocity (PWV). Single and multiple sprint interval exercise sessions caused similar changes in all variables. Heart rate was increased throughout recovery (p < 0.05), while central artery PWV was increased until 20 min of recovery (p < 0.05) and lower extremity PWV was decreased until ~45 min (p < 0.05). Distensibility of the superficial femoral artery showed a trend for a reduction at 2 min post-exercise (p = 0.06). These results indicate that extremely high intensity exercise transiently increases central artery stiffness, while metabolite induced vasodilation reduces peripheral stiffness in exercised limbs well into recovery.