Contribution of central and peripheral adaptations to changes in maximal oxygen uptake following 4 weeks of sprint interval training.

The current study examined the contribution of central and peripheral adaptations to changes in maximal oxygen uptake (V̇O2max) following sprint interval training (SIT). Twenty-three males completed 4 weekly SIT sessions (8 × 20-s cycling bouts at ∼170% of work rate at V̇O2max, 10-s recovery) for 4 weeks. Following completion of training, the relationship between changes in V̇O2max and changes in central (cardiac output) and peripheral (arterial-mixed venous oxygen difference (a-vO2diff), muscle capillary density, oxidative capacity, fibre-type distribution) adaptations was determined in all participants using correlation analysis. Participants were then divided into tertiles on the basis of the magnitude of their individual V̇O2max responses, and differences in central and peripheral adaptations were examined in the top (HI; ∼10 mL·kg-1·min-1 increase in V̇O2max, p < 0.05) and bottom (LO; no change in V̇O2max, p > 0.05) tertiles (n = 8 each). Training had no impact on maximal cardiac output, and no differences were observed between the LO group and the HI group (p > 0.05). The a-vO2diff increased in the HI group only (p < 0.05) and correlated significantly (r = 0.71, p < 0.01) with changes in V̇O2max across all participants. Muscle capillary density (p < 0.02) and ß-hydroxyacyl-CoA dehydrogenase maximal activity (p < 0.05) increased in both groups, with no between-group differences (p > 0.05). Citrate synthase maximal activity (p < 0.01) and type IIA fibre composition (p < 0.05) increased in the LO group only. Collectively, although the heterogeneity in the observed V̇O2max response following 4 weeks of SIT appears to be attributable to individual differences in systemic vascular and/or muscular adaptations, the markers examined in the current study were unable to explain the divergent V̇O2max responses in the LO and HI groups.

Acute beetroot juice administration improves peak isometric force production in adolescent males.

The purpose of this study was to examine the effects of acute beetroot juice (BR) administration on repeated sprint performance and isometric force production in adolescent males. Twelve male adolescents (age, 16.8 ± 1.0 years; height, 178.8 ± 9.2 cm; mass, 74.8 ± 12.5 kg; peak height velocity, 2.53 ± 1.2 years) participated in this double-blind, placebo-controlled, crossover designed study. Participants consumed 2 × 70 mL of BR (∼12.9 mmol NO3-; Beet It Sport) or a nitrate-depleted placebo (PL) at 2.5 h prior to performing isometric mid-thigh pulls (IMTP) and 4 repeated 20-s Wingate sprints interspersed with 4 min of rest. Sprint data were analyzed by a 2 × 4 (group × time) repeated-measures ANOVA while a dependent t test was used to compare conditions for IMTP peak force. A significant main effect for time (p < 0.05) was observed for peak power (PP), average power (Pavg), and fatigue index (FI) across sprints. Compared with sprint 1, sprint 4 resulted in significant decreases in PP (p < 0.000; -16.6%) and Pavg (p = 0.000; -21.8%) and FI was significantly elevated (p < 0.000; 15.2%). No significant group × time interactions were observed between conditions for PP (p = 0.402), Pavg (p = 0.479), or FI (p = 0.37). IMTP peak force was significantly higher (p = 0.004; 13.9%) following BR consumption compared with PL. The repeated sprint protocol resulted in significant fatigue while BR did not influence sprint performance. However, it appears BR administration may improve peak force production in adolescent males.

The influence of high-intensity interval training and moderate-intensity continuous training on sedentary time in overweight and obese adults.

High-intensity interval training (HIIT) elicits health benefits but it is unclear how HIIT impacts sedentary behaviour. In this preliminary study, we compared the effects of supervised HIIT or moderate-intensity continuous training (MICT) on sedentary time in overweight/obese adults. In both groups, percentage of time spent in sedentary activities was significantly reduced during the supervised exercise intervention (time main effect, P = 0.03), suggesting that both HIIT and MICT replaced time spent previously being sedentary.

A multi-ingredient nutritional supplement enhances exercise training-related reductions in markers of systemic inflammation in healthy older men.

We evaluated whether twice-daily consumption of a multi-ingredient nutritional supplement (SUPP) would reduce systemic inflammatory markers following 6 weeks of supplementation alone (phase 1), and the subsequent addition of 12 weeks of exercise training (phase 2) in healthy older men, in comparison with a carbohydrate-based control (CON). Tumour necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) concentrations were progressively reduced (P-time < 0.05) in the SUPP group. No change in TNF-α or IL-6 concentrations was observed in the CON group.

Modified sprint interval training protocols: physiological and psychological responses to 4 weeks of training.

Sprint interval training (SIT) protocols involving brief (≤15 s) work bouts improve aerobic and anaerobic performance, highlighting peak speed generation as a potentially important adaptive stimulus. To determine the physiological and psychological effects of reducing the SIT work bout duration, while maintaining total exercise and recovery time, 43 healthy males (n = 27) and females (n = 16) trained for 4 weeks (3 times/week) using one of the following running SIT protocols: (i) 30:240 (n = 11; 4-6 × 30-s bouts, 4 min rest); (ii) 15:120 (n = 11; 8-12 × 15-s bouts, 2 min rest); (iii) 5:40 (n = 12; 24-36 × 5-s bouts, 40 s rest); or (iv) served as a nonexercising control (n = 9). Protocols were matched for total work (2-3 min) and rest (16-24 min) durations, as well as the work-to-rest ratio (1:8 s). Pre- and post-training measures included a graded maximal oxygen consumption test, a 5-km time trial, and a 30-s maximal sprint test. Self-efficacy, enjoyment, and intentions were assessed following the last training session. Training improved maximal oxygen consumption (5.5%; P = 0.006) and time-trial performance (5.2%; P = 0.039), with a main effect of time for peak speed (1.7%; P = 0.042), time to peak speed (25%; P < 0.001), and body fat percentage (1.4%; P < 0.001) that appeared to be driven by the training. There were no group effects for self-efficacy (P = 0.926), enjoyment (P = 0.249), or intentions to perform SIT 3 (P = 0.533) or 5 (P = 0.951) times/week. This study effectively demonstrated that the repeated generation of peak speed during brief SIT work bouts sufficiently stimulates adaptive mechanisms promoting increases in aerobic and anaerobic capacity.

Modified sprint interval training protocols. Part I. Physiological responses.

Adaptations to sprint interval training (SIT) are observed with brief (≤15-s) work bouts highlighting peak power generation as an important metabolic stimulus. This study examined the effects of manipulating SIT work bout and recovery period duration on energy expenditure (EE) during and postexercise, as well as postexercise fat oxidation rates. Nine active males completed a resting control session (CTRL) and 3 SIT sessions in randomized order: (i) 30:240 (4 × 30-s bouts, 240-s recovery); (ii) 15:120 (8 × 15-s bouts, 120-s recovery); (3) 5:40 (24 × 5-s bouts, 40-s recovery). Protocols were matched for the total duration of work (2 min) and recovery (16 min), as well as the work-to-recovery ratio (1:8 s). EE and fat oxidation rates were derived from gas exchange measured before, during, and for 3 h postexercise. All protocols increased EE versus CTRL (P < 0.001). Exercise EE was greater (P < 0.001) with 5:40 (209 kcal) versus both 15:120 (163 kcal) and 30:240 (138 kcal), while 15:120 was also greater (P < 0.001) than 30:240. Postexercise EE was greater (P = 0.014) with 15:120 (313 kcal) versus 5:40 (294 kcal), though both were similar (P > 0.077) to 30:240 (309 kcal). Postexercise fat oxidation was similar (P = 0.650) after 15:120 (0.104 g·min-1) and 30:240 (0.116 g·min-1) and both were greater (P < 0.030) than 5:40 (0.072 g·min-1) and CTRL (0.049 g·min-1). In conclusion, shorter SIT work bouts that target peak power generation increase exercise EE without compromising postexercise EE, though longer bouts promote greater postexercise fat utilization.

Modified sprint interval training protocols. Part II. Psychological responses.

Sprint-interval training (SIT) is a viable method to improve health and fitness. However, researchers have questioned the utility of SIT because of its strenuous nature. The current study aimed to determine if manipulating the sprint and recovery duration, while maintaining the 1:8 work to rest ratio, could uncover a more favourable SIT protocol. Nine healthy active males (age, 23.3 ± 3.0 years; body mass index, 22.4 ± 2.2 kg·m-2; maximal oxygen consumption, 48.9 ± 5.3 mL·kg-1·min-1) participated in 3 experimental running SIT sessions: (i) 30:240 (4 × 30-s efforts, 240-s recovery), (ii) 15:120 (8 × 15-s efforts, 120-s recovery), (iii) 5:40 (24 × 5-s efforts, 40-s recovery), and (iv) a final behavioural choice follow-up session. Affect, intentions, task self-efficacy, enjoyment, and preference were evaluated. Midway through exercise, affect became more positive for 5:40 compared with 30:240 (p < 0.05) and postexercise affect was greater for both 5:40 (p = 0.014) and 15:120 (p = 0.015) compared with 30:240. Participants expressed greater intentions to perform 5:40 3 and 5 times/week compared with 15:120 and 30:240 (p < 0.05). Participants felt more confident in their ability to perform 5:40 (p = 0.001) and 15:120 (p = 0.008) compared with 30:240. The 5:40 session was also rated as more enjoyable than 15:120 (p = 0.025) and 30:240 (p = 0.026). All participants preferred the 5:40 protocol. These data suggest that shorter sprints with more repetitions are perceived as more enjoyable and lead to greater intentions to engage in SIT.

Preliminary safety analysis of high-intensity interval training (HIIT) in persons with chronic stroke.

The purpose of this study was to assess safety via electrocardiographic (ECG), blood pressure (BP), heart rate (HR), and orthopedic responses to 3 different high-intensity interval training (HIIT) protocols in persons with stroke. Eighteen participants (10 male; 61.9 + 8.3 years of age; 5.8 + 4.2 years poststroke) completed a symptom-limited graded exercise test (GXT) with ECG monitoring to screen for eligibility and determine HR peak. The 3 HIIT protocols involved repeated 30 s bursts of treadmill walking at maximum speed alternated with rest periods of 30 s (P30), 1 min (P60), or 2 min (P120). Sessions were performed in random order and included 5 min warm up, 20 min HIIT, and 5 min cool down. Variables measured included ECG activity, BP, HR, signs and symptoms of cardiovascular intolerance, and orthopedic concerns. Generalized linear mixed models and Tukey-Kramer adjustment were used to compare protocols using p < 0.05. No signs or symptoms of cardiovascular intolerance, significant arrhythmias, ST segment changes, or orthopedic responses resulted in early termination of any HIIT session. HIIT elicited HRs in excess of 88% of measured HRpeak including 6 (P30), 8 (P60), and 2 (P120) participants eliciting a HR response above their GXT HRpeak. Both maximum BP and HR were significantly higher in P30 and P60 relative to P120. Preliminary data indicate that persons with chronic stroke who have been prescreened with an ECG stress test, a symptom-limited GXT, and a harness for fall protection may safely participate in HIIT, generating substantially higher HRs than what is seen in traditional moderate intensity training.

A group-enhanced sprint interval training program for amateur athletes.

Sprint interval training (SIT) can elicit improvements in aerobic and anaerobic capacity. While variations in SIT protocols have been investigated, the influence of social processes cannot be overlooked. As research supports the use of groups to influence individual cognitions and behaviours, the current project assessed the effectiveness of a group-based intervention with participants conducting SIT. Specifically, 53 amateur athletes (age, 21.9 ± 2.9 years; 53% females) took part in a 4-week training program (3 sessions per week, 30-s "all-out" efforts with 4 min active recovery, repeated 4-6 times per session), and were assigned to "true group", aggregate, or individual conditions. Results indicated no significant differences between groups for the physiological measures. With regards to training improvements from baseline for all participants- regardless of condition - significant main effects for time were identified for maximal oxygen uptake (2.5-2.8 mL·kg(-1)·min(-1), p < 0.001, η(2) = 0.03), time-trial performance (14-32 s, p < 0.001, η(2) = 0.37), and anaerobic power (1.1-1.7 k·h(-1), p < 0.001, η(2) = 0.66). With regards to the psychological measures, significant main effects between groups were found for motivation (p = 0.033, η(2) = 0.13), task self-efficacy (p = 0.018, η(2) = 0.15), and scheduling self-efficacy (p = 0.003, η(2) = 0.22). The true group experienced greater improvements in motivation than the individual condition, but the aggregate and individual conditions demonstrated greater increases in task and scheduling self-efficacy. Though the SIT paradigm employed induced training improvements similar to previous work, the group intervention was not able to further these improvements.

Incidence of nonresponse and individual patterns of response following sprint interval training.

The current study sought to explore the incidence of nonresponders for maximal or submaximal performance following a variety of sprint interval training (SIT) protocols. Data from 63 young adults from 5 previously published studies were utilized in the current analysis. Nonresponders were identified using 2 times the typical error (TE) of measurement for peak oxygen uptake (2 × TE = 1.74 mL/(kg·min)), lactate threshold (2 × TE = 15.7 W), or 500 kcal time-to-completion (TTC; 2 × TE = 306 s) trial. TE was determined on separate groups of participants by calculating the test-retest variance for each outcome. The overall rate of nonresponders for peak oxygen uptake across all participants studied was 22% (14/63) with 4 adverse responders observed. No nonresponders for peak oxygen uptake were observed in studies where participants trained 4 times per week (n = 18), while higher rates were observed in most studies requiring training 3 times per week (30%-50%; n = 45). A nonresponse rate of 44% (8/18) and 50% (11/22) was observed for the TTC test and lactate threshold, respectively. No significant correlations were observed between the changes in peak oxygen uptake and TTC (r = 0.014; p = 0.96) or lactate threshold (r = 0.17; p = 0.44). The current analysis demonstrates a significant incidence of nonresponders for peak oxygen uptake and heterogeneity in the individual patterns of response following SIT. Additionally, these data support the importance of training dose and suggest that the incidence of nonresponse may be mitigated by utilizing the optimal dose of SIT.

Effect of jumping interval training on neuromuscular and physiological parameters: a randomized controlled study.

This study analyzed the effect of 4 weeks of jumping interval training (JIT), included in endurance training, on neuromuscular and physiological parameters. Eighteen recreational runners, randomized in control and experimental groups, performed 40 min of running at 70% of velocity at peak oxygen uptake, for 3 times per week. Additionally, the experimental group performed the JIT twice per week, which consisted of 4 to 6 bouts of continuous vertical jumps (30 s) with 5-min intervals. Three days before and after the training period, the countermovement (CMJ) and continuous jump (CJ30), isokinetic and isometric evaluation of knee extensors/flexors, progressive maximal exercise, and submaximal constant-load exercise were performed. The JIT provoked improvement in neuromuscular performance, indicated by (i) increased jump height (4.7%; effect size (ES) = 0.99) and power output (≈ 3.7%; ES ≈ 0.82) of CMJ and rate of torque development of knee extensors in isometric contraction (29.5%; ES = 1.02); (ii) anaerobic power and capacity, represented by the mean of jump height (7.4%; ES = 0.8), and peak power output (PPO) (5.6%; ES = 0.73) of the first jumps of CJ30 and the mean of jump height (10.2%, ES = 1.04) and PPO (9.5%, ES = 1.1), considering all jumps of CJ30; and (iii) aerobic power and capacity, represented by peak oxygen uptake (9.1%, ES = 1.28), velocity at peak oxygen uptake (2.7%, ES = 1.11), and velocity corresponding to the onset of blood lactate accumulation (9.7%, ES = 1.23). These results suggest that the JIT included in traditional endurance training induces moderate to large effects on neuromuscular and physiological parameters.

The kinetics of blood lactate in boys during and following a single and repeated all-out sprints of cycling are different than in men.

This study characterized the impact of high-intensity interval training on the kinetics of blood lactate and performance in trained boys and men. Twenty-one boys (11.4 ± 0.8 years) and 19 men (29.4 ± 5.0 years) performed a set of four 30-s sprints with 2-min of rest and a single 30-s sprint on 2 separate occasions (randomized order) with assessment of performance. Blood lactate was assayed after each sprint and during 30 min of recovery from both tests. The individual time-curves of blood lactate concentration were fitted to the biexponential function as follows: [Formula: see text], where the velocity parameters γ1 and γ2 reflect the capacity to release lactate from the previously active muscle into the blood and to subsequently eliminate lactate from the organism, respectively. In both tests, peak blood lactate concentration was significantly lower in the boys (four 30-s sprints: 12.2 ± 3.6 mmol·L(-1); single 30-s sprint: 8.7 ± 1.8 mmol·L(-1)) than men (four 30-s sprints: 16.1 ± 3.3 mmol·L(-1); single 30-s sprint: 11.5 ± 2.1; p < 0.001). The boys exhibited faster γ1 (1.4531 ± 0.65 min; p < 0.001) and γ2 (0.059 ± 0.023 min; p = 0.01) in the single 30-s sprint and faster γ2 (0.049 ± 0.016 min; p = 0.01) in the four 30-s sprints. The worsening of performance from the first to the last of the four 30-s sprints was less pronounced in boys (9.2% ± 13.9%) than men (19.2% ± 11.5%; p = 0.01). In the present study boys, when compared with men, exhibited lower Peak blood lactate concentration; less pronounced decline in performance during the sprints concomitantly with more rapid release and elimination during the single 30-s sprint; and faster elimination of lactate following the four 30-s sprints.

The influence of nighttime feeding of carbohydrate or protein combined with exercise training on appetite and cardiometabolic risk in young obese women.

Single macronutrient intake prior to sleep reduces appetite but may negatively impact insulin sensitivity in sedentary obese women. The present study examined the additive impact of nighttime feeding of whey (WH), casein (CAS), or carbohydrate (CHO) combined with exercise training on appetite, cardiometabolic health, and strength in obese women. Thirty-seven sedentary obese women (WH, n = 13, body mass index (BMI) 34.4 ± 1.3 kg/m(2); CAS, n = 14, BMI 36.5 ± 1.8 kg/m(2); CHO, n = 10, BMI 33.1 ± 1.7 kg/m(2)) consumed WH, CAS, or CHO (140-150 kcal/serving), every night of the week, within 30 min of sleep, for 4 weeks. Supervised exercise training (2 days of resistance training and 1 day of high-intensity interval training) was completed 3 days per week. Pre- and post-testing measurements included appetite ratings, mood state, resting metabolic rate, fasting lipids, glucose, and hormonal responses (insulin, leptin, adiponectin, hs-CRP, IGF-1, and cortisol), body composition, and strength. Nighttime intake of CAS significantly (p < 0.05) increased morning satiety (pretraining, 25 ± 5; post-training 41 ± 6) more than WH (pretraining, 34 ± 5; post-training, 35 ± 6) or CHO (pre 40 ± 8, post 43 ± 7). Exercise training increased lean mass and strength, decreased body fat, and improved mood state in all groups. No other differences were noted. Nighttime feeding of CAS combined with exercise training increased morning satiety more than WH or CHO. Nighttime feeding for 4 weeks did not impact insulin sensitivity (assessed via homeostatic model assessment of insulin resistance) when combined with exercise training in obese women. ClinicalTrial.gov: NCT01830946.

Resveratrol supplementation does not augment performance adaptations or fibre-type-specific responses to high-intensity interval training in humans.

The present study examined the effect of concurrent exercise training and daily resveratrol (RSV) supplementation (150 mg) on training-induced adaptations following low-dose high-intensity interval training (HIIT). Sixteen recreationally active (∼22 years, ∼51 mL·kg(-1)·min(-1)) men were randomly assigned in a double-blind fashion to either the RSV or placebo group with both groups performing 4 weeks of HIIT 3 days per week. Before and after training, participants had a resting muscle biopsy taken, completed a peak oxygen uptake test, a Wingate test, and a submaximal exercise test. A main effect of training (p < 0.05) and interaction effect (p < 0.05) on peak aerobic power was observed; post hoc pairwise comparisons revealed that a significant (p < 0.05) increase occurred in the placebo group only. Main effects of training (p < 0.05) were observed for both peak oxygen uptake (placebo - pretraining: 51.3 ± 1.8, post-training: 54.5 ± 1.5 mL·kg(-1)·min(-1), effect size (ES) = 0.93; RSV - pretraining: 49.6 ± 2.2, post-training: 52.3 ± 2.5 mL·kg(-1)·min(-1), ES = 0.50) and Wingate peak power (placebo: pretraining: 747 ± 39, post-training: 809 ± 31 W, ES = 0.84; RSV - pretraining: 679 ± 39, post-training: 691 ± 43 W, ES = 0.12). Fibre-type distribution was unchanged, while a main effect of training (p < 0.05) was observed for succinate dehydrogenase activity and glycogen content, but not α-glycerophosphate dehydrogenase activity or intramuscular lipids in type I and IIA fibres. The fold change in PGC-1α, SIRT1, and SOD2 gene expression following training was significantly (p < 0.05) lower in the RSV group than placebo. These results suggest that concurrent exercise training and RSV supplementation may alter the normal training response induced by low-volume HIIT.