Sprint Interval Cycling Research Articles

Brain hemodynamic changes during sprint interval cycling exercise and recovery periods

The prefrontal cortex (PFC) is one of the most investigated brain regions on exercise due to its relationship with maintaining exercise. This study aims to demonstrate the effects of a high-intensity exercise on cerebral hemodynamic parameters in the PFC and how physical load reflects on PFC. Twelve male (mean ± SD: age = 20 ± 1.56 years) performed the Wingate Anaerobic Test (WAnT; 30-s all-out) for three repetitions as a Sprint Interval Training (SIT) exercise model via a cycling ergometer with 4 min of active recovery (50 W, 50 rpm) between the repetitions. A functional Near-infrared Spectroscopy (fNIRS) device was used to record hemodynamic changes of the prefrontal cortex throughout the entire protocol. The oxy-hemoglobin (oxy-Hb) and total-hemoglobin (total-Hb) levels in the PFC were increased significantly ( P < 0.001), while the power outputs were decreased in repetitive WAnT's ( P < 0.05). The oxy-Hb values were higher than the pre-exercise values even in the recovery periods between WAnT's ( P < 0.001). In conclusion, repeated load with the active recovery periods might be an optimal approach for increasing the PFC oxygenation to its peak values. These results suggest that a repeated Wingate test could be used as a test to improve the metabolic condition of the athlete's brain. Le cortex préfrontal (PFC) est l’une des régions cérébrales les plus étudiées pendant l’exercice. Cette étude vise à démontrer les effets d’un exercice de haute intensité sur les paramètres hémodynamiques cérébraux dans le PFC et comment la charge physique se reflète sur le PFC. Douze athlètes masculins (moyenne ± ET : âge = 20 ± 1,56 ans) ont effectué un test anaérobie Wingate (WAnT ; 30 s) à trois répétitions en tant que modèle d’exercice Sprint, Interval Training (SIT) sur un vélo ergomètre (Monark 894E ; Vansbro, Sweden) avec 4 minutes de récupération active (50 W, 50 tr/min) entre les répétitions. La spectroscopie fonctionnelle proche infrarouge (fNIRS) a été utilisée pour enregistrer les changements hémodynamiques dans le cortex préfrontal tout au long du protocole. Les niveaux d’oxy-hémoglobine (oxy-Hb) et d’hémoglobine totale (total-Hb) dans le PFC ont augmenté de manière significative ( p < 0,001) et les résultats de puissance ont diminué au cours des WAnT répétés ( p < 0,05). Les valeurs d’oxy-Hb au cours des WAnT répétés étaient supérieures à celles du repos, et cela même dans les périodes de récupération entre les WAnT ( p < 0,001). Des sprints répétés, séparés par des périodes de récupération actives, pourraient être une approche optimale pour augmenter l’oxygénation du PFC. Ces résultats suggèrent que la répétition de tests Wingate peut être utilisée pour améliorer l’état métabolique du cerveau des athlètes.

Comparisons Between Normobaric Normoxic and Hypoxic Recovery on Post-exercise Hemodynamics After Sprint Interval Cycling in Hypoxia.

The aim of this study was to investigate the effects of either normoxic or hypoxic recovery condition on post-exercise hemodynamics after sprint interval leg cycling exercise rather than hemodynamics during exercise. The participants performed five sets of leg cycling with a maximal effort (30 s exercise for each set) with a 4-min recovery of unloaded cycling between the sets in hypoxia [fraction of inspired oxygen (FiO2) = 0.145]. The load during pedaling corresponded to 7.5% of the individual’s body weight at the first set, and it gradually reduced from 6.5 to 5.5%, 4.5, and 3.5% for the second to fifth sets. After exercise, the participants rested in a sitting position for 30 min under normoxia (room-air) or hypoxia. Mean arterial pressure decreased over time during recovery (p < 0.001) with no condition and interaction effects (p > 0.05). Compared to pre-exercise values, at 30 min after exercise, mean arterial pressure decreased by 5.6 ± 4.8 mmHg (mean ± standard deviation) during hypoxic recovery, and by 5.3 ± 4.6 mmHg during normoxic recovery. Peripheral arterial oxygen saturation (SpO2) at all time points (5, 10, 20, and 30 min) during hypoxic recovery was lower than during normoxic recovery (all p < 0.05). The area under the hyperemic curve of tissue oxygen saturation (StO2) at vastus lateralis defined as reperfusion curve above the baseline values during hypoxic recovery was lower than during normoxic recovery (p < 0.05). Collectively, post-exercise hypotension after sprint interval leg cycling exercise was not affected by either normoxic or hypoxic recovery despite marked differences in SpO2 and StO2 during recovery between the two conditions.

Warm-Up With Added Respiratory Dead Space Volume Mask Improves the Performance of the Cycling Sprint Interval Exercise: Cross-Over Study.

Special breathing exercises performed during warm-up lead to hypercapnia and stimulation of mechanisms leading to increased exercise performance, but the effect of a device that increases the respiratory dead space volume (ARDSv) during warm-up has not been studied. The purpose of this study was to investigate the effect of 10 min warm-up with ARDSv on performance, physiological and biochemical responses during sprint interval cycling exercise (SIE). During four laboratory visits at least 72 h apart, they completed: (1) an incremental exercise test (IET) on a cycloergometer, (2) a familiarization session, and cross-over SIE sessions conducted in random order on visits (3) and (4). During one of them, 1200 mL of ARDSv was used for breathing over a 10-min warm-up. SIE consisted of 6 × 10-s all-out bouts with 4-min active recovery. Work capacity, cardiopulmonary parameters, body temperature, respiratory muscle strength, blood acid-base balance, lactate concentration, and rating of perceived exertion (RPE) were analyzed. After warm-up with ARDSv, PETCO2 was 45.0 ± 3.7 vs. 41.6 ± 2.5 (mm Hg) (p < 0.001). Body temperature was 0.6 (°C) higher after this form of warm-up (p < 0.05), bicarbonate concentration increased by 1.8 (mmol⋅L–1) (p < 0.01). As a result, work performed was 2.9% greater (p < 0.01) compared to the control condition. Respiratory muscle strength did not decreased. Warming up with added respiratory dead space volume mask prior to cycling SIE produces an ergogenic effect by increasing body temperature and buffering capacity.

Physiological responses to maximal 4s sprint interval cycling using inertial loading: the influence of inter-sprint recovery duration.

Interval exercise allows very high-power outputs to be maintained, a key for stimulating training adaptations. The main purpose of this study was to develop a sprint interval protocol that stimulated both anaerobic and aerobic systems while maximizing power output and minimizing fatigue. The secondary goal was to investigate the influence of inter-sprint recovery duration. Sixteen (8 females) participants (age: 23.5 ± 3.4 years, peak oxygen consumption (VO2peak): 45.6 ± 9.2mlkg-1min-1) took part in this study. The exercise protocol involved 30 bouts of 4s maximal cycling sprints using an 'Inertial Load Ergometer'. Recovery durations between sprints of 15, 30 and 45s were studied in three trials. Peak power output (PPO) was maintained while taking 45 and 30s of recovery, although it was 9% higher (p < 0.05) during 45 vs. 30s. PPO with 15s recovery declined 18% (p < 0.05) and then stabilized as did oxygen consumption (72±2% VO2peak) at a level that might reflect the peak rate of ATP-PC resynthesis from oxidative metabolism. The 15-, 30-, and 45s trials elicited 72, 56, and 49% VO2peak and 86, 80, and 75% of maximal heart rate (all p<0.001). Perceived exertion increased with shorter recovery periods but remained at 12.6-14.7 and never became 'very hard'. The present study describes the use of an inertial-load ergometer to accommodate repeated 4s maximal cycling sprints that elicit 72% VO2peak when the recovery period is 15s. However, a recovery duration of 15s was insufficient for the maintenance of power generation. NCT04448925, 26 Jun 2020; retrospectively registered to clinicaltrials.gov.

Ingestion of Carbohydrate Prior to and during Maximal, Sprint Interval Cycling Has No Ergogenic Effect: A Randomized, Double-Blind, Placebo Controlled, Crossover Study.

Carbohydrate (CHO) ingestion may improve intermittent sprint performance in repeated sprint efforts ≤15 s. Yet, evidence for its efficacy on sprint interval durations ~30 s is lacking. The purpose of this study was to investigate the effects of CHO ingestion on maximal sprint interval exercise. Fifteen (n = 15) recreational athletes (13/2 males/females, age 22 ± 2 years; height 176 ± 11 cm; mass 76.8 ± 11.3 kg) volunteered for this randomised, double-blind, placebo-controlled, crossover design. Participants completed two experimental trials (performed 10-days apart) involving the ingestion of an 8% CHO solution or a flavour and appearance-matched placebo (PLA) solution (5 mL/kg/bw), immediately before exercise, and preceding the second interval of four × 30 s bouts of repeated maximal sprint efforts (separated by 3.5 min of passive recovery). Peak and mean power (W) output progressively decreased during the repeated sprints (main effect of time, p < 0.0001), but there were no differences between CHO and PLA during any of the sprints (p > 0.05 for condition main effect and condition × time interaction). Physiological responses (blood lactate, heart rate, oxygen consumption, respiratory exchange ratio and RPE) were also unaltered by CHO ingestion. In conclusion, CHO ingestion does not enhance performance or modulate physiological responses during intermittent maximal, sprint cycling.

Physiological Responses And Energetic Of Two Sprint Interval Exercise Protocols Based On Rope-skipping And Cycling

High-intensity interval training could improve performance effectively. However, the acute physiological response and energy expenditure of a low-volume, high-intensity rope-skipping based protocol have not been determined. PURPOSE: To compare the physiological response and energy resource in repeated bouts of sprint interval cycling (SIC) and high-intensity intermittent double-under rope skipping (HIT-RS). METHOD: Fifteen college students (age=20.2±0.8yrs, body mass=67.7±4.8kg, BMI=22.4±1.2kg.m-2, VO2peak=51.90±7.83ml.kg-1.min-1) volunteered for this study. Participants completed two protocols (4⊆30s with 4min active recovery) on separate days with 1 week between trials. VO2 and heart rate were monitored at rest, during test and continue to 1 hour after test. Blood lactate was measured 3 minutes after each bout, and minute by minute after the last bout. Lactic (WBla) and alactic anaerobic (WPCr) energy outputs were calculated from net lactate production and the fast component of EPOC. Aerobic metabolism (Waer) was determined from VO2 during exercise. RESULT: Mean values for %VO2peak and %HRpeak for SIC (78.79±15.35% and 85.33±4.69%) and HIT-RS (74.93±16.21% and 83.17±5.37%) were not significantly different (p>0.05). The overall energy cost for SIC (102.75±13.15 kJ) was significantly higher (p<0.001) compared to HIT-RS (70.86±10.25 kJ). Waer, WBla and WPCr for SIC (17.39±3.08, 59.50±8.10 and 25.86±5.40 kJ) and HIT-RS (13.05±2.01, 27.97±6.77 and 29.84±6.28 kJ) were significantly different (p<0.01). Fractions of Waer, WBla and WPCr for SIC (16.92±1.77%, 57.99±4.70% and 25.09±3.65%) and HIT-RS (18.80±3.13%, 38.84±6.09% and 42.36±5.98%) were significantly different (p<0.001). Both protocols were anaerobic-dominated with similar fraction (SIC:83.08±3.01% vs HIT-RS: 81.20±4.52%). Compared to SIC, HIT-RS was more PCr dominant (42.36±5.98% vs 25.09±3.65%, p<0.01) with lower anaerobic lactic contribution (38.84±6.09% vs 57.99±4.70%, p<0.001). CONCLUSION: High-intensity interval protocol of rope skipping elicits vigorous cardiorespiratory responses and may confer physiological adaptations and performance improvements resembling as SIC.

Sex-Based Performance Responses to an Acute Sprint Interval Cycling Training Session in Collegiate Athletes

ABSTRACT There are limited data pertaining to the effects of sex on sprint interval cycling (SIC) training session performance. Purpose: We investigated sex-based differences on sprint interval cycling (SIC) performance in collegiate soccer players. Methods: Twelve men and twelve women completed two identical lab trials, 7–14 days apart. The first lab session served as familiarization, “dry run,” trial. Reported data were collected and analyzed during the second, “testing” SIC training trial. Each SIC training session was comprised of a warm-up, at 50 revolutions per min (RPM) with no resistance, and six repeated 30-s Wingate Anaerobic Tests (WAnT) separated by a 4-min recovery period between each sprint. Results: Significant (P ≤ .05) sex differences were observed in peak power (PP), peak power relative to body mass (RPP), mean power (MP), mean power relative to body mass (RMP) but not in peak power relative to fat free mass (FFMPP). When WAnT bouts 2–6 were expressed as %Δ of WAnT1, there were no significant (P > .05) differences between the sexes across all performance variables. Further, Cohen’s d statistics demonstrated only trivial and small effect size between the groups. Average HR and RPE were not significantly (P > .05) different between the sexes. Correlational analysis revealed a significant (P ≤ .05) relationship between FFM, and PP and MP. Conclusion: Although overall performance may be affected by a number of physiological mechanisms, the results of the current study indicate that differences between men and women soccer players performing SIC training, are likely attributed to differences in body composition.

Modulation of Endothelial Glycocalyx and Microcirculation in Healthy Young Men during High-Intensity Sprint Interval Cycling-Exercise by Supplementation with Pomegranate Extract. A Randomized Controlled Trial.

The natural components of the pomegranate fruit may provide additional benefits for endothelial function and microcirculation. It was hypothesized that supplementation with pomegranate extract might improve glycocalyx properties and microcirculation during acute high-intensity sprint interval cycling exercise. Eighteen healthy and recreationally active male volunteers 22–28 years of age were recruited randomly to the experimental and control groups. The experimental group was supplemented with pomegranate extract 20 mL (720 mg phenolic compounds) for two weeks. At the beginning and end of the study, the participants completed a high-intensity sprint interval cycling-exercise protocol. The microcirculation flow and density parameters, glycocalyx markers, systemic hemodynamics, lactate, and glucose concentration were evaluated before and after the initial and repeated (after 2 weeks supplementation) exercise bouts. There were no significant differences in the microcirculation or glycocalyx over the course of the study (p < 0.05). The lactate concentration was significantly higher in both groups after the initial and repeated exercise bouts, and were significantly higher in the experimental group compared to the control group after the repeated bout: 13.2 (11.9–14.8) vs. 10.3 (9.3–12.7) mmol/L, p = 0.017. Two weeks of supplementation with pomegranate extract does not influence changes in the microcirculation and glycocalyx during acute high-intensity sprint interval cycling-exercise. Although an unexplained rise in blood lactate concentration was observed.

Pre-Exercise Perceptions of Energy and Fatigue are Significantly Related to Performance during Sprint Interval Cycling

Pre-Exercise Perceptions of Energy and Fatigue are Significantly Related to Performance during Sprint Interval Cycling

Interactive Virtual Reality Reduces Quadriceps Pain during High-Intensity Cycling.

Brief, high-intensity cycling is popular because physiological benefits accrue with a short workout time, but burning pain in the quadriceps is a potential barrier to engaging in this type of exercise. Virtual reality (VR) can temporarily decrease pain, but its effect on muscle pain during high-intensity exercise is unknown. The primary purpose of this experiment was to test whether adding interactive VR (I-VR) to high-intensity cycling could reduce quadriceps pain or improve performance. Ninety-four adults who were physically active in their leisure time and age 18 to 29 yr completed three 30-s sprint interval cycling trials at a high resistance (0.085- and 0.075-kg resistance to the flywheel per kilogram body weight for men and women, respectively). In this randomized between-subject experiment, participants cycled while wearing a head-mounted display and viewing either (i) a dynamically changing cityscape perceived as interactively cycling through a virtual city (I-VR group) or (ii) a static picture of the cityscape with instructions to mentally imagine cycling through that city (static VR/motor imagery control group). Sphericity-adjusted 2 × 3 (group-time) ANOVA revealed a significant group-time interaction (F = 4.568; df = 1.499, 133.301; ηp = 0.047, P = 0.021) for pain intensity. With I-VR, pain intensities were 13.3% (mean, 4.60 vs 5.31; d = 0.28) and 11.8% (mean, 5.68 vs 6.44; d = 0.27) lower at sprint trials 2 and 3, respectively. The group-time interaction (P = 0.412) was not significant for total work. Compared with a static VR/motor imagery control condition, I-VR during brief, high-intensity, fatigue-inducing leg cycling attenuates quadriceps pain intensity without reducing performance.

Cold-water immersion after training sessions: effects on fiber type-specific adaptations in muscle K+ transport proteins to sprint-interval training in men.

Effects of regular use of cold-water immersion (CWI) on fiber type-specific adaptations in muscle K+ transport proteins to intense training, along with their relationship to changes in mRNA levels after the first training session, were investigated in humans. Nineteen recreationally active men (24 ± 6 yr, 79.5 ± 10.8 kg, 44.6 ± 5.8 ml·kg-1·min-1) completed six weeks of sprint-interval cycling, either without (passive rest; CON) or with training sessions followed by CWI (15 min at 10°C; COLD). Muscle biopsies were obtained before and after training to determine abundance of Na+, K+-ATPase isoforms (α1-3, β1-3) and phospholemman (FXYD1) and after recovery treatments (+0 h and +3 h) on the first day of training to measure mRNA content. Training increased ( P < 0.05) the abundance of α1 and β3 in both fiber types and β1 in type-II fibers and decreased FXYD1 in type-I fibers, whereas α2 and α3 abundance was not altered by training ( P > 0.05). CWI after each session did not influence responses to training ( P > 0.05). However, α2 mRNA increased after the first session in COLD (+0 h, P < 0.05) but not in CON ( P > 0.05). In both conditions, α1 and β3 mRNA increased (+3 h; P < 0.05) and β2 mRNA decreased (+3 h; P < 0.05), whereas α3, β1, and FXYD1 mRNA remained unchanged ( P > 0.05) after the first session. In summary, Na+,K+-ATPase isoforms are differently regulated in type I and II muscle fibers by sprint-interval training in humans, which, for most isoforms, do not associate with changes in mRNA levels after the first training session. CWI neither impairs nor improves protein adaptations to intense training of importance for muscle K+ regulation. NEW & NOTEWORTHY Although cold-water immersion (CWI) after training and competition has become a routine for many athletes, limited published evidence exists regarding its impact on training adaptation. Here, we show that CWI can be performed regularly without impairing training-induced adaptations at the fiber-type level important for muscle K+ handling. Furthermore, sprint-interval training invoked fiber type-specific adaptations in K+ transport proteins, which may explain the dissociated responses of whole-muscle protein levels and K+ transport function to training previously reported.

A Hydrothermally Processed Maize Starch and Its Effects on Blood Glucose Levels During High-Intensity Interval Exercise.

Hetrick, MM, Naquin, MR, Gillan, WW, Williams, BM, and Kraemer, RR. A hydrothermally processed maize starch and its effects on blood glucose levels during high-intensity interval exercise. J Strength Cond Res 32(1): 3-12, 2018-A hydrothermally processed maize starch (HPMS) has been shown to blunt initial blood glucose and insulin response during endurance activity at 70% maximal oxygen uptake (V[Combining Dot Above]O2max). High-intensity interval training (HIIT) is a form of exercise that has many health benefits although it is only performed for short periods of time with interspersed rest periods. The purpose of this study was to compare the blood glucose and associated metabolic stress responses to a sprint interval cycling (SIC) exercise protocol (a form of HIIT) with and without an HPMS in a healthy population. Fourteen subjects completed a total of 4 sessions: a preliminary session, an SIC session with HPMS, an SIC session without HPMS, and a control session in which only HPMS was ingested. Blood glucose, blood lactate, respiratory exchange ratio, oxygen consumption, and rating of perceived exertion responses were recorded during the sessions. There was a significant and progressive rise in blood glucose levels during each of the cycle sprints of both exercise sessions, but not a significant difference between treatment or nontreatment SIC sessions. This is the first study to determine blood glucose responses to SIC after each sprint interval and to report that ingestion of HPMS does not affect glucose responses to SIC. The findings provide some preliminary evidence suggesting subjects at risk for glucose excursions could use SIC to improve health through monitoring blood glucose concentrations during SIC and if necessary, modifying number, intensity, and duration of sprints completed.

Psychological and Physiological Biomarkers of Neuromuscular Fatigue after Two Bouts of Sprint Interval Exercise.

The main aim of our study was to determinate whether a repeated bout (RB) (vs. first bout [FB]) of sprint interval cycling exercise (SIE) is sufficient to mitigate SIE-induced psychological and physiological biomarker kinetics within 48 h after the exercise. Ten physically active men (age, 22.6 ± 5.2 years; VO2max, 44.3 ± 5.7 ml/kg/min) performed the FB of SIE (12 repeats of 5 s each) on one day and the RB 2 weeks later. The following parameters were measured: motor performance (voluntary, electrically induced and isokinetic skeletal muscle contraction torque, and central activation ratio [CAR]); stress markers [brain-derived neurotrophic factor (BDNF), cortisol, norepinephrine, and epinephrine]; inflammatory markers (IL-6, IL-10, and TNF-α); metabolic markers (glucose and lactate); muscle and rectal temperature; cycling power output; and psychological perceptions. The average cycling power output and neuromuscular fatigue after exercise did not differ between the FB and RB. There were significant decreases in cortisol and BDNF concentration at 12 h (P < 0.05) and 24 h (P < 0.001) after the FB, respectively. The decrease in cortisol concentration observed 12 h after exercise was significantly greater after the RB (P < 0.05) than after the FB. The immune-metabolic response to the RB (vs. FB) SIE was suppressed and accompanied by lower psychological exertion. Most of the changes in psychological and physiological biomarkers in the FB and RB were closely related to the response kinetics of changes in BDNF concentration.

Moderate, but not vigorous, intensity exercise training reduces C-reactive protein

Background: Sprint interval cycle training is a contemporary popular mode of training but its relative efficacy, under conditions of matched energy expenditure, to reduce risk factors for cardiometabolic disease is incompletely characterised, especially in young women. The purpose of this investigation was to determine the relative efficacy of six weeks of moderate-intensity cycling (MOD-C) and vigorous sprint-interval cycling (VIG-SIC) on lipid profile, insulin (INS) and insulin resistance using the homeostatic model assessment (HOMA-IR) and C-reactive protein (CRP) in inactive, overweight/obese (OW/OB) young women.Methods: Participants (BMI ≥25 kg/m2, waist circumference ≥88 cm) were randomly assigned to MOD-C (20–30 min at 60–70% of heart rate reserve(HRR)) or VIG-SIC (5–7 repeated bouts 30-second maximal effort sprints, followed by four minutes of active recovery) supervised training three days/week for six weeks, with each group matched on energy expenditure. Adiposity (%Fat) was measured using dual x-ray absorptiometry.Results: Forty-four participants (20.4 ± 1.6 years, 65.9% Caucasian, 29.8 ± 4.1 kg/m2) were included in the analysis. The improvement in CRP observed in the MOD-C group was larger than the VIG-C group (p = .034). Overall, high-density lipoprotein (HDL-C) and low-density lipoprotein (LDL-C) levels improved following training (p < .05); however, total cholesterol, triglyceride, INS and HOMA-IR did not improve (p > .05).Conclusion: These results indicate MOD-C training may be more effective in reducing CRP than VIG-SIC.

Sex Differences In Total Pyy And Glp-1 After Moderate-intensity Continuous And Sprint Interval Cycling Exercise.

Exercise is often used as a weight-loss strategy, however, exercise interventions are sometimes less effective in females than males for improving body composition. One possible explanation is that exercise affects appetite regulating hormones differently in males and females such that females increase post-exercise energy intake. Recently, sprint interval training was shown to reduce body fat in females despite relatively low energy expenditure during exercise. PURPOSE: To examine sex differences in circulating anorexigenic hormones and perceived hunger following an acute session of sprint interval training (SIT) and moderate-intensity continuous training (MICT). METHODS: Twenty-one active participants (11 females in early follicular phase) participated in 3 sessions in a randomized crossover design: 1) MICT, 30 min cycling at 65% VO2max; 2) SIT, 6 x 30 sec “all-out” cycling sprints with 4 min recovery periods (27 min total); and 3) control (CTRL; no exercise). Participants arrived at the lab fasted and consumed a standardized breakfast 1 hour before exercise. Blood samples were collected pre-exercise, immediately and 90 min post-exercise for the measurement of total peptide tyrosine tyrosine (PYY) and glucagon-like peptide-1 (GLP-1). Subjective perceptions of hunger were assessed using a visual analogue scale before breakfast and before all blood draws. Hormone data were analysed as change in concentration from baseline. Changes in hormones and hunger were analysed using a 3 x 3 x 2 mixed factor (session x time x sex) repeated measures ANOVA. RESULTS: Increases in GLP-1 and PYY were greater during the MICT session (P<0.05) and SIT session (P<0.01) compared to CTRL. Total PYY increased more immediately post-exercise in males than females (P=0.030). GLP-1 increased only in females following MICT (P=0.034) and SIT (P=0.024) compared to CTRL. Perceived hunger was lower immediately post-MICT (P=0.016) and SIT (P=0.006) compared to CTRL, but there were no sex differences. CONCLUSION: Total PYY and GLP-1 appear to respond similarly to submaximal and supramaximal exercise, however, these results suggest they may respond differently to exercise in males and females over 90 min. The post-exercise hormonal response we observed in females would not be expected to create a compensatory increase in energy intake.

Sex differences in the response of total PYY and GLP-1 to moderate-intensity continuous and sprint interval cycling exercise.

Exercise interventions are often less effective at improving body composition for females than males, potentially due to post-exercise hormonal responses that increase energy intake in females. Recently, sprint interval training was shown to effectively reduce body fat in females despite being relatively low during exercise energy expenditure. To determine whether any sex difference in total PYY, GLP-1 or perceived hunger exists following moderate-intensity continuous exercise (MICT) and sprint interval exercise (SIT) METHODS: Twenty-one active participants (11 females) participated in three sessions in a randomized crossover design: (1) MICT, 30-min cycling at 65% VO2max; (2) SIT, 6 × 30s "all-out" sprints with 4-min recovery periods; (3) control (CTRL; no exercise). Blood samples were collected pre-exercise, immediately and 90min post-exercise for the measurement of total PYY and GLP-1. Subjective perceptions of hunger were assessed using a visual analogue scale pre-breakfast and before all blood samples. Concentrations of total PYY and GLP-1 were greater during MICT (P = 0.05) and SIT (P = 0.005) compared to CTRL. Total PYY increased more immediately post-exercise in males than females (P = 0.030). GLP-1 only increased in females following MICT (P = 0.034) and SIT (P = 0.024) compared to CTRL. Perceived hunger was lower immediately post-MICT (P = 0.016) and SIT (P = 0.006) compared to CTRL. These results suggest that total PYY and GLP-1 respond differently to exercise in males and females over 90min following various exercise intensities. The observed post-exercise hormonal response would not be expected to create a compensatory increase in energy intake in females.

Total PYY and GLP-1 responses to submaximal continuous and supramaximal sprint interval cycling in men

Exercise-induced changes in appetite-regulating hormones may be intensity-dependent, however a clear dose-response relationship has not been established. The purpose of this study was to examine changes in anorexigenic markers (total PYY and GLP-1) in response to rest or exercise at submaximal and supramaximal intensities. Ten active males completed four experimental sessions in randomized order: 1) Moderate intensity continuous training (MICT; 30 min cycling at 65% VO2max); 2) High intensity continuous training (HICT; 30 min cycling at 85% VO2max); 3) Sprint interval training (SIT; 6 × 30 s “all-out” cycling bouts with 4 min recovery periods); 4) Control (CTRL; no exercise). Blood samples were obtained immediately pre- and post-exercise, as well as 90-min post-exercise for the measurement of total PYY and GLP-1. Subjective hunger was assessed using a visual analog scale pre-breakfast and at the three blood sampling time-points. Total PYY concentrations increased immediately post-exercise following both HICT (P = 0.006) and SIT (P < 0.001) versus CTRL, while SIT was also greater (P = 0.005) compared to MICT. Total GLP-1 concentrations changed similarly across time-points (P < 0.001), with no differences between sessions (P = 0.280). Perceptions of hunger also changed similarly across time-points (P < 0.001) with no differences between trials (P = 0.085). These findings suggest that total PYY increases only after high-intensity exercise and exhibits a greater responsiveness to SIT compared to moderate-intensity exercise. Compensatory increases in hunger do not seem to occur at any exercise intensity. These findings support a dose-response relationship between exercise intensity and total PYY, though the effects on total GLP-1 and hunger perceptions seem unclear.

Effects of Sprint Interval Cycling on Fatigue, Energy, and Cerebral Oxygenation.

Feelings of fatigue are reduced after a session of continuous exercise of low-to-moderate intensity lasting 20 min or more, but only when feelings of energy are increased. Feelings of fatigue and energy have not been described after fatiguing, high-intensity interval exercise. Cerebral oxygenation has been implicated as a central correlate of fatigability, but it has not been studied concurrent with perceived fatigue during or after exercise. Fifteen recreationally active participants (8 women, 7 men) completed bouts of sprint interval cycling (four, 30-s all-out sprints each followed by 4 min of active recovery) and a time- and work-matched bout of constant resistance cycling. Oxygenation (oxygenated hemoglobin [HbO2]) and deoxygenation (deoxygenated hemoglobin [HHb]) in the dorsolateral prefrontal cortex were measured using near-infrared spectroscopy. Fatigue ratings during each sprint and feelings of fatigue and energy during recovery were assessed. Increases in HbO2 and HHb in frontal cortex were greater during sprint cycling than during constant resistance cycling (P = 0.001). Fatigability (decreased power output) increased over successive sprints (P = 0.001). About 95% of the increase in fatigue ratings across sprints (P < 0.001) was accounted for by fatigability and cortical HbO2. Feelings of fatigue were decreased (P < 0.001) and feelings of energy were increased (P < 0.05) across sprint recovery periods but were unchanged during constant resistance cycling. About 85% of the changes in feelings of fatigue or energy during recovery were explained by fatigue ratings across sprints and maximum HbO2 in the cortex during recovery. Repeated, high-intensity sprints were fatiguing, but paradoxical reductions in feelings of fatigue and increases in feelings of energy occurred during recovery that were accounted for by ratings of fatigue during exercise and oxygenation in the dorsolateral prefrontal cortex during recovery.

Comparison of Cardiorespiratory and Metabolic Responses in Kettlebell High-Intensity Interval Training Versus Sprint Interval Cycling

The purpose of this study was to determine the effectiveness of a novel exercise protocol we developed for kettlebell high-intensity interval training (KB-HIIT) by comparing the cardiorespiratory and metabolic responses to a standard sprint interval cycling (SIC) exercise protocol. Eight men volunteered for the study and completed 2 preliminary sessions, followed by two 12-minute sessions of KB-HIIT and SIC in a counterbalanced fashion. In the KB-HITT session, 3 circuits of 4 exercises were performed using a Tabata regimen. In the SIC session, three 30-second sprints were performed, with 4 minutes of recovery in between the first 2 sprints and 2.5 minutes of recovery after the last sprint. A within-subjects' design over multiple time points was used to compare oxygen consumption (V[Combining Dot Above]O2), respiratory exchange ratio (RER), tidal volume (TV), breathing frequency (f), minute ventilation (VE), caloric expenditure rate (kcal·min), and heart rate (HR) between the exercise protocols. Additionally, total caloric expenditure was compared. A significant group effect, time effect, and group × time interaction were found for V[Combining Dot Above]O2, RER, and TV, with V[Combining Dot Above]O2 being higher and TV and RER being lower in the KB-HIIT compared with the SIC. Only a significant time effect and group × time interaction were found for f, VE, kcal·min, and HR. Additionally, total caloric expenditure was found to be significantly higher during the KB-HIIT. The results of this study suggest that KB-HIIT may be more attractive and sustainable than SIC and can be effective in stimulating cardiorespiratory and metabolic responses that could improve health and aerobic performance.

Acute responses of circulating microRNAs to low-volume sprint interval cycling.

Low-volume high-intensity interval training is an efficient and practical method of inducing physiological responses in various tissues to develop physical fitness and may also change the expression of circulating microRNAs (miRNAs). The purpose of the present study was to examine whether miRNAs for muscle, heart, somatic tissue and metabolism were affected by 30-s intervals of intensive sprint cycling. We also examined the relationship of these miRNAs to conventional biochemical and performance indices. Eighteen healthy young males performed sprint interval cycling. Circulating miRNAs in plasma were detected using TaqMan-based quantitative PCR and normalized to Let-7d/g/i. In addition, we determined the levels of insulin-like growth factor-I, testosterone and cortisol, and anaerobic capacity. Compared to plasma levels before exercise muscle-specific miR-1 (0.12 ± 0.02 vs. 0.09 ± 0.02), miR-133a (0.46 ± 0.10 vs. 0.31 ± 0.06), and miR-133b (0.19 ± 0.02 vs. 0.10 ± 0.01) decreased (all P < 0.05), while miR-206 and miR-499 remained unchanged. The levels of metabolism related miR-122 (0.62 ± 0.07 vs. 0.34 ± 0.03) and somatic tissues related miR-16 (1.74 ± 0.27 vs. 0.94 ± 0.12) also decreased (both P < 0.05). The post-exercise IGF-1 and cortisol concentrations were significantly increased, while testosterone concentrations did not. Plasma levels of miR-133b correlated to peak power (r = 0.712, P = 0.001) and miR-122 correlated to peak power ratio (r = 0.665, P = 0.003). In conclusion sprint exercise provokes genetic changes for RNA related to specific muscle or metabolism related miRNAs suggesting that miR-133b and miR-122 may be potential useful biomarkers for actual physiological strain or anaerobic capacity. Together, our findings on the circulating miRNAs may provide new insight into the physiological responses that are being performed during exercise and delineate mechanisms by which exercise confers distinct phenotypes and improves performance.