Acute Effects of Sprint Interval Training and Blood Flow Restriction on Neuromuscular and Muscle Function.

BFR) applied during sprint interval training (SIT) on performance and neuromuscular function. METHODS: Fifteen men completed a randomized bout of SIT with CBFR, IBFR, and without BFR (No-BFR), consisting of 2, 30-s maximal sprints on a cycle ergometer with a resistance of 7.5% of body mass. Concentric peak torque (CPT), maximal voluntary isometric contraction (MVIC) torque, and muscle thickness (MT) were measured before and after SIT, including surface electromyography (sEMG) recorded during the strength assessments. Peak and mean revolutions per minute (RPM) were measured during SIT and power output was examined relative to physical working capacity at the fatigue threshold (PWCFT). RESULTS: CPT and MVIC torque decreased from pre-SIT (220.3±47.6 Nm and 355.1±72.5 Nm, respectively) to post-SIT (147.9±27.7 Nm and 252.2±45.5 Nm, respectively, all P<0.05), while MT increased (1.77±0.31 cm to 1.96±0.30 cm). sEMG mean power frequency decreased during CPT (-12.8±10.5%) and MVIC (-8.7±10.2%) muscle actions. %PWCFT was greater during No-BFR (414.2±121.9%) than CBFR (375.9±121.9%). CONCLUSION: SIT with or without BFR induced comparable alterations in neuromuscular fatigue and sprint performance across all conditions, without affecting neuromuscular function.

Acute Effects of Continuous and Intermittent Blood Flow Restriction on Sprint Interval Performance and Muscle Oxygen Responses.

ABSTRACT: Wizenberg, AM, Gonzalez-Rojas, D, Rivera, PM, Proppe, CE, Laurel, KP, Stout, JR, Fukuda, DH, Billaut, F, Keller, JL, and Hill, EC. Acute effects of continuous and intermittent blood flow restriction on sprint interval performance and muscle oxygen responses. J Strength Cond Res 37(10): e546-e554, 2023-This investigation aimed to examine the acute effects of continuous and intermittent blood flow restriction (CBFR and IBFR, respectively) during sprint interval training (SIT) on muscle oxygenation, sprint performance, and ratings of perceived exertion (RPE). Fifteen men (22.6 ± 2.4 years; 176 ± 6.3 cm; 80.0 ± 12.6 kg) completed in random order a SIT session with CBFR, IBFR (applied during rest), and no blood flow restriction (NoBFR). Each SIT session consisted of two 30-second all-out sprint tests separated by 2 minutes. Peak power (PP), total work (TW), sprint decrement score (S dec ), RPE, and muscle oxygenation were measured during each sprint. A p value ≤0.05 was considered statistically significant. PP decreased to a greater extent from sprint 1 to sprint 2 during CBFR (25.5 ± 11.9%) and IBFR (23.4 ± 9.3%) compared with NoBFR (13.4 ± 8.6%). TW was reduced similarly (17,835.6 ± 966.2 to 12,687.2 ± 675.2 J) from sprint 1 to sprint 2 for all 3 conditions, but TW was lower (collapsed across time) for CBFR (14,320.7 ± 769.1 J) than IBFR (15,548.0 ± 840.5 J) and NoBFR (15,915.4 ± 771.5 J). There were no differences in S dec (84.3 ± 1.7%, 86.1 ± 1.5%, and 87.2 ± 1.1% for CBFR, IBFR, and NoBFR, respectively) or RPE, which increased from sprint 1 (8.5 ± 0.3) to sprint 2 (9.7 ± 0.1). Collective muscle oxygenation responses increased across time and were similar among conditions, whereas increases in deoxy[heme] and total[heme] were greatest for CBFR. Applying BFR during SIT induced greater decrements in PP, and CBFR resulted in greater decrements in work across repeated sprints. The larger increases in deoxy[heme] and total[heme] for CBFR suggested it may induce greater metabolite accumulation than IBFR and NoBFR when combined with SIT.

Running exercise with end-expiratory breath holding up to the breaking point induces large and early fall in muscle oxygenation.

PURPOSE: The goal of this study was to assess the effects of repeated running bouts with end-expiratory breath holding (EEBH) up to the breaking point on muscle oxygenation. METHODS: Eight male runners participated in three randomised sessions each including two exercises on a motorised treadmill. The first exercise consisted in performing 10-12 running bouts with EEBH of maximum duration either (separate sessions) at 60% (active recovery), 80% (passive recovery) or 100% (passive recovery) of the maximal aerobic velocity (MAV). Each repetition started at the onset of EEBH and ended at its release. In the second exercise of the session, subjects replicated the same procedure but with normal breathing (NB). Arterial oxygen saturation (SpO2), heart rate (HR) and the change in vastus lateralis muscle deoxy-haemoglobin/myoglobin (Δ[HHb/Mb]) and total haemoglobin/myoglobin (Δ[THb/Mb]) were continuously monitored throughout exercises. RESULTS: On average, the EEBHs were maintained for 10.1 ± 1.1 s, 13.2 ± 1.8 s and 12.2 ± 1.7 s during exercise at 60%, 80% and 100% of MAV, respectively. In the three exercise intensities, SpO2 (mean nadir values: 76.3 ± 2.5 vs 94.5 ± 2.5%) and HR were lower with EEBH than with NB at the end of the repetitions; whereas, the mean Δ[HHb/Mb] (12.6 ± 5.2 vs 7.7 ± 4.4 µm) and Δ[THb/Mb] (- 0.6 ± 2.3 vs 3.8 ± 2.6 µm) were, respectively, higher and lower with EEBH (p < 0.05). CONCLUSION: This study showed that performing repeated bouts of running exercises with EEBH up to the breaking point induced a large and early drop in muscle oxygenation compared with the same exercise with NB. This phenomenon was probably the consequence of the strong arterial oxygen desaturation induced by the maximal EEBHs.

The effect of HIIT vs. SIT on muscle oxygenation in trained sprint kayakers.

PURPOSE: To assess the performance change and physiological adaptations following nine sessions of short high-intensity interval training (HIIT) or sprint-interval training (SIT) in sprint kayakers. METHODS: Twelve trained kayakers performed an incremental test and 3 time trials (200 m, 500 m and 1000 m) on a kayak ergometer. Oxygen consumption (V̇O2) and muscle oxygenation of the latissimus dorsi, biceps brachii, and vastus lateralis were measured. Athletes were then paired for sex and V̇O2max and randomized into a HIIT or a SIT training group, and performed nine training sessions before repeating the tests. RESULTS: Training improved performance in HIIT (200 m: + 3.8 ± 3.1%, p = 0.06; 500 m: + 2.1 ± 4.1%, p = 0.056; 1000 m: + 3.0 ± 4.6%, p = 0.13) but changes in performance remained within the smallest worthwhile change in SIT (200 m: + 0.8 ± 4.1%, p = 0.59; 500 m: + 0.5 ± 4.1%, p = 0.87; 1000 m: + 1.3 ± 4.6%, p = 0.57). In the 1000 m, training led to a greater deoxygenation in the biceps brachii and vastus lateralis in HIIT, and in the latissimus dorsi in SIT. In HIIT, the best predictors of improvements in 1000 m performance were increases in latissimus dorsi and vastus lateralis maximal deoxygenation. CONCLUSION: In a group of trained sprint kayakers, greater improvements in performance can be obtained with HIIT compared with SIT, for any distance. Training did not change V̇O2peak, but increased muscle maximal deoxygenation, suggesting both HIIT and SIT elicit peripheral adaptations. Performance improvement in the 1000 m was associated with increased maximal muscle deoxygenation, reinforcing the contribution of peripheral adaptations to performance in sprint kayaking.

Fifteen days of moderate normobaric hypoxia does not affect mitochondrial function, and related genes and proteins, in healthy men.

PURPOSE: To investigate within the one study potential molecular and cellular changes associated with mitochondrial biogenesis following 15 days of exposure to moderate hypoxia. METHODS: Eight males underwent a muscle biopsy before and after 15 days of hypoxia exposure (FiO2 = 0.140-0.154; ~ 2500-3200 m) in a hypoxic hotel. Mitochondrial respiration, citrate synthase (CS) activity, and the content of genes and proteins associated with mitochondrial biogenesis were investigated. RESULTS: Our main findings were the absence of significant changes in the mean values of CS activity, mitochondrial respiration in permeabilised fibers, or the content of genes and proteins associated with mitochondrial biogenesis, after 15 days of moderate normobaric hypoxia. CONCLUSION: Our data provide evidence that 15 days of moderate normobaric hypoxia have negligible influence on skeletal muscle mitochondrial content and function, or genes and proteins content associated with mitochondrial biogenesis, in young recreationally active males. However, the increase in mitochondrial protease LON content after hypoxia exposure suggests the possibility of adaptations to optimise respiratory chain function under conditions of reduced O2 availability.

Sport-Specific Agility and Change of Direction in Water Polo: The Reliability and Validity of Two Newly Developed Tests.

ABSTRACT: Dong, L, Paradelo, D, Delorme, A, Oliveira, J, Parillo, B, Croteau, F, Romeas, T, Dubé, E, Bieuzen, F, Billaut, F, and Berryman, N. Sport-specific agility and change of direction in water polo: The reliability and validity of two newly developed tests. J Strength Cond Res 35(12S): S111-S118, 2021-There is a gap in water-based agility testing that considers both the change-of-direction (COD) and perceptive-reactive components of agility. This study sought to develop easily implementable, sport-specific in-water agility tests for water polo and to verify the reliability and validity of these new tests: the in-water Stop and Go (SG) and Jump and Go (JG). Female water polo athletes at the Senior (n = 12, age = 22.1 ± 2.1 years), Junior (n = 19, age = 18.5 ± 1.0 years), and Youth (n = 11, age = 16.5 ± 0.8 years) national levels performed 3 trials of each of the SG, JG, and the existing Functional Test for Agility Performance (FTAP). Senior athletes performed an additional experimental session to assess reliability parameters. Relative reliability for agility and COD versions of the SG and JG was high or very high (intraclass correlation coefficient [ICC] = 0.76-0.95). For construct validity analyses, significant between-group differences for each of the new tests (p < 0.05) were found. In contrast, the FTAP was moderately reliable (ICC = 0.57) and was unsuccessful in discriminating between playing levels. Considering the favorable metrological properties of the SG and JG, their fidelity to in-game demands, and their accessible setups, these new tests represent viable options to implement at grassroots and elite levels for the assessment and training of water polo-specific agility.

Neuromuscular and perceptual responses during repeated cycling sprints-usefulness of a "hypoxic to normoxic" recovery approach.

PURPOSE: We investigated the consequence of varying hypoxia severity during an initial set of repeated cycling sprints on performance, neuromuscular fatigability, and exercise-related sensations during a subsequent set of repeated sprints in normoxia. METHODS: Nine active males performed ten 4-s sprints (recovery = 30 s) at sea level (SL; FiO2 ~ 0.21), moderate (MH; FiO2 ~ 0.17) or severe normobaric hypoxia (SH; FiO2 ~ 0.13). This was followed, after 8 min of passive recovery, by five 4-s sprints (recovery = 30 s) in normoxia. RESULTS: Mean power decrement during Sprint 10 was exacerbated in SH compared to SL and MH (- 34 ± 12%, - 22 ± 13%, - 25 ± 14%, respectively, p < 0.05). Sprint performance during Sprint 11 recovered to that of Sprint 1 in all conditions (p = 0.267). All exercise-related sensations at Sprint 11 recovered significantly compared to Sprint 1, with no difference for Set 2 (p > 0.05). Ratings of overall perceived discomfort, difficulty breathing, and limb discomfort were exacerbated during Set 1 in SH versus SL (p < 0.05). Compared to SL, the averaged MPO value for Set 2 was 5.5 ± 3.0% (p = 0.003) lower in SH. Maximal voluntary force and twitch torque decreased similarly in all conditions immediately after Set 1 (p < 0.05), without further alterations after Set 2. Peripheral and cortical voluntary activation values did not change (p > 0.05). CONCLUSION: Exercise-related sensations, rather than neuromuscular function integrity, may play a pivotal role in influencing performance of repeated sprints and its recovery.

Capsaicin Supplementation during High-intensity Continuous Exercise: A Double-blind Study.

To investigate the effect of acute capsaicin (CAP) supplementation on time to exhaustion, physiological responses and energy systems contribution during continuous high-intensity exercise session in runners. Fifteen recreationally-trained runners completed two randomized, double-blind continuous high-intensity exercises at the speed eliciting 90% V̇O2peak (90% s V̇O2peak), 45 minutes after consuming capsaicin or an isocaloric placebo. Time to exhaustion, blood lactate concentration, oxygen consumption during and 20-min post-exercise, energy systems contribution, time to reach V̇O2peak, heart rate and the rate of perceived exertion (RPE) were evaluated. There was no significant difference between conditions for time to reach V̇O2peak (CAP:391.71±221.8 vs. PLA:298.20±174.5 sec, ES:0.58, p=0.872), peak lactate (CAP:7.98±2.11 vs. PLA:8.58±2.15 µmol, ES:-0.28, p=0.257), time to exhaustion (CAP:654.28±195.44 vs. PLA:709.20±208.44 sec, ES:-0.28, p=0.462, end-of-exercise heart rate (CAP:177.6±14.9 vs. PLA:177.5±17.9 bpm, ES:-0.10, p=0.979) and end-of-exercise RPE (CAP: 19±0.8 vs. PLA: 18±2.4, ES: 0.89, p=0.623). In conclusion, acute CAP supplementation did not increase time to exhaustion during high-intensity continuous exercise nor alter physiological responses in runners.

Similar Recovery of Maximal Cycling Performance after Ischemic Preconditioning, Neuromuscular Electrical Stimulation or Active Recovery in Endurance Athletes.

This study investigated the efficacy of ischemic preconditioning (IPC) on the recovery of maximal aerobic performance and physiological responses compared with commonly used techniques. Nine endurance athletes performed two 5-km cycling time trials (TT) interspersed by 45 minutes of recovery that included either IPC, active recovery (AR) or neuromuscular electrical stimulation (NMES) in a randomized crossover design. Performance, blood markers, arterial O2 saturation (SpO2), heart rate (HR), near-infrared spectroscopy-derived muscle oxygenation parameters and perceptual measures were recorded throughout TTs and recovery. Differences were analyzed using repeated-measures ANOVAs and Cohen's effect size (ES). The decrement in chronometric performance from TT1 to TT2 was similar between recovery modalities (IPC: -6.1 sec, AR: -7.9 sec, NMES: -5.4 sec, p = 0.84, ES 0.05). The modalities induced similar increases in blood volume before the start of TT2 (IPC: 13.3%, AR: 14.6%, NMES: 15.0%, p = 0.79, ES 0.06) and similar changes in lactate concentration and pH. There were negligible differences between conditions in bicarbonate concentration, base excess of blood and total concentration of carbon dioxide, and no difference in SpO2, HR and muscle O2 extraction during exercise (all p > 0.05). We interpreted these findings to suggest that IPC is as effective as AR and NMES to enhance muscle blood volume, metabolic by-products clearance and maximal endurance performance. IPC could therefore complement the athlete's toolbox to promote recovery.

Effects of inspiratory muscle warm-up on locomotor muscle oxygenation in elite speed skaters during 3000 m time trials.

PURPOSE: It has been shown that an inspiratory muscle warm-up (IMW) could enhance performance. IMW may also improve the near-infrared spectroscopy (NIRS)-derived tissue oxygen saturation index (TSI) during cycling. However, there exists contradictory data about the effect of this conditioning strategy on performance and muscle oxygenation. We examined the effect of IMW on speed skating performance and studied the underpinning physiological mechanisms related to muscle oxygenation. METHODS: In a crossover, randomized, single-blind study, eight elite speed skaters performed 3000 m on-ice time trials, preceded by either IMW (2 × 30 breaths, 40% maximal inspiratory pressure) or SHAM (2 × 30 breaths, 15% maximal inspiratory pressure). Changes in TSI, oxyhemoglobin-oxymyoglobin ([O2HbMb]), deoxyhemoglobin-deoxymyoglobin ([HHbMb]), total hemoglobin-myoglobin ([THbMb]) and HHbMbdiff ([O2HbMb]-[HHbMb]) in the right vastus lateralis muscle were monitored by NIRS. All variables were compared at different time points of the race simulation with repeated-measures analysis of variance. Differences between IMW and SHAM were also analyzed using Cohen's effect size (ES) ± 90% confidence limits, and magnitude-based inferences. RESULTS: Compared with SHAM, IMW had no clear impact on skating time (IMW 262.88 ± 17.62 s vs. SHAM 264.05 ± 21.12 s, effect size (ES) 0.05; 90% confidence limits, - 0.22, 0.32, p = 0.7366), TSI, HbMbdiff, [THbMb], [O2HbMb] and perceptual responses. CONCLUSIONS: IMW did not modify skating time during a 3000 m time trial in speed skaters, in the conditions of our study. The unchanged [THbMb] and TSI demonstrate that the mechanisms by which IMW could possibly exert an effect on performance were unaffected by this intervention.

Capsaicin supplementation increases time to exhaustion in high-intensity intermittent exercise without modifying metabolic responses in physically active men.

PURPOSE: The purpose of this study was to investigate the acute effect of capsaicin supplementation on performance and physiological responses during high-intensity intermittent exercise (HIIE). METHOD: Thirteen physically active men (age = 24.4 ± 4.0 years; height = 176.4 ± 6.9 cm; body mass = 78.7 ± 13.8 kg; running training per week = 3.9 ± 0.9 h) performed an incremental running test to determine peak oxygen uptake ([Formula: see text]) and the speed associated with [Formula: see text] (s[Formula: see text]). Thereafter, subjects completed two randomized, double-blind HIIE (15s:15 s at 120% s[Formula: see text]) trials 45-min after consuming capsaicin (12 mg) or an isocaloric placebo. Time to exhaustion, blood lactate concentration, oxygen consumption during and 20 min post-exercise, energy expenditure, time spent above 90% of [Formula: see text], and the rate of perceived exertion were evaluated. RESULTS: There was no difference between capsaicin and placebo for any variable except time to exhaustion [capsaicin: 1530 ± 515 s (102 efforts) vs placebo: 1342 ± 446 s (89 efforts); p < 0.001]. CONCLUSION: In conclusion, capsaicin supplementation increased time to exhaustion in high-intensity intermittent exercise without modifying the metabolic response of exercise or the rate of perceived exertion in physically active men. Capsaicin could be used to increase the training load during specific exercise training sessions.

Repeated Treadmill Sprints Impair Cognitive Performance in Amateur Team-Sport Athletes When Performed in Normobaric Hypoxia.

This study determined if a single bout of repeated-sprint running under hypoxic (RSH) conditions was associated with impaired cognitive function when compared with repeated-sprint running under normoxic (RSN) conditions. Eleven amateur team-sport athletes performed a repeated-sprint running protocol (4 sets of 4, 4-s all-out sprints; i.e., RSR444) under both conditions (14.5% and 20.9% O2) on a non-motorized treadmill. Changes in SpO2, pre-frontal cortex total haemoglobin (Δ[THb]), oxyhaemoglobin (Δ[O2Hb]), deoxyhaemoglobin (Δ[HHb]) and cognitive function (detection task: DET; identification task: IDN; one card learning task: OCL; performed pre and 20 min post RSR444) were examined. During RSH, SpO2 was lower following each set (p ≤ 0.05), while [HHb] was higher after each set (p ≤ 0.05) compared with RSN. In addition, while there was no effect of condition on DET (p = 0.20) or IDN (p = 0.14), OCL accuracy was lower after, compared with before, RSH (p=0.04), but not RSN (p = 0.52). A significant relationship was observed between Δ[HHB] and ΔOCL accuracy (r = -0.68, p = 0.01). Performance of a single bout of RSH with 14.5% O2 resulted in impaired cognitive function in amateur team-sport athletes. Coaches should be mindful of timing of RSH prescription with regard to other training sessions that challenge speed and movement accuracy.

Cerebral oxygenation declines but does not impair peak oxygen uptake during incremental cycling in women using oral contraceptives.

PURPOSE: To compare prefrontal cortex oxygenation in recreationally-active women using oral contraceptives (WomenOC; n = 8) to women with a natural menstrual cycle (WomenNC; n = 8) during incremental exercise to exhaustion. METHODS: Participants performed incremental cycling to exhaustion to determine lactate threshold 1 (LT1) and 2 (LT2) and peak oxygen uptake (VO2peak). Prefrontal cortex oxygenation was monitored via near-infrared spectroscopy through concentration changes in oxy-haemoglobin (Δ[HbO2]), deoxy-haemoglobin (Δ[HHb]), total-haemoglobin (Δ[tHb]) and tissue saturation index (TSI). RESULTS: 17ß-oestradiol and progesterone were lower in WomenOC (35 ± 26; 318 ± 127 pmol·L-1, respectively) than WomenNC (261 ± 156; 858 ± 541 pmol·L-1, respectively). There were no differences in full blood examination results or serum nitric oxide (p > 0.05). However, WomenOC presented lower concentrations in ferric-reducing ability of plasma (- 8%; effect size; ES - 0.52 ± 0.61), bilirubin (- 32%; ES - 0.56 ± 0.62) and uric acid (- 17%; ES - 0.53 ± 0.61). Cardiopulmonary parameters were similar between groups during cycling, including VO2peak (p = 0.99). While there was a significant effect of time on all parameters measured by near-infrared spectroscopy during incremental cycling, there was no effect of OC at LT1, LT2 or exhaustion calculated as a change from baseline (TSI; p = 0.096, Δ[HbO2]; p = 0.143, Δ[HHb]; p = 0.085 and Δ[tHb]; p = 0.226). The change in TSI from LT1 to LT2 was significantly different between groups (WomenNC; mean difference + 2.06%, WomenOC; mean difference - 1.73%; p = 0.003). CONCLUSION: Prefrontal tissue oxygenation declined at a lower relative exercise intensity in WomenOC as compared to WomenNC, however, this did not influence VO2peak. The results provide the first evidence for variance in the cerebral oxygenation response to exercise, which may be associated with female sex hormones.

Knee extensor fatigue developed during high-intensity exercise limits lower-limb power production.

We investigated the association between changes in vastii electromyography (EMG) and knee extensor fatigue during high-intensity cycling, and the subsequent effect on lower-limb power and intermuscular coordination during all-out cycling. On two separate days, participants completed 30-s all-out cycling or 10-min of high-intensity cycling followed by 30-s all-out cycling. EMG for gluteus maximus (GMAX), rectus femoris (RF), vastii (VAS), hamstrings (HAM) and gastrocnemius (GAS); co-activation for GMAX/RF, VAS/HAM and VAS/GAS; isometric maximal voluntary force (IMVF) and resting twitch (RT) of the knee extensors were measured. VAS EMG increases during high-intensity cycling (6% to 14%, P < 0.05) were negatively correlated (r = -0.791, P < 0.05) with knee extensor IMVF decreases (-2% to-36%, P < 0.05) following the exercise. Knee extensor IMVF decreases were positively correlated (r = 0.757, P < 0.05) with all-out cycling power reductions (0% to -27%, P < 0.05). VAS/GAS co-activation did not change (P > 0.05) during all-out cycling while VAS and GAS EMG decreased. Larger increase in VAS EMG during high-intensity cycling was associated with greater knee extensor fatigue and larger power reduction during all-out cycling. High VAS/GAS co-activation potentially limited power reduction induced by knee extensor fatigue during all-out cycling.

Effects of Lower-Limb Strength Training on Agility, Repeated Sprinting With Changes of Direction, Leg Peak Power, and Neuromuscular Adaptations of Soccer Players.

Hammami, M, Negra, Y, Billaut, F, Hermassi, S, Shephard, RJ, and Chelly, MS. Effects of lower-limb strength training on agility, repeated sprinting with changes of direction, leg peak power, and neuromuscular adaptations of soccer players. J Strength Cond Res 32(1): 37-47, 2018-We examined the effects on explosive muscular performance of incorporating 8 weeks strength training into the preparation of junior male soccer players, allocating subjects between an experimental group (E, n = 19) and a matched control group (C, n = 12). Controls maintained their regular training program, but the experimental group replaced a part of this schedule by strength training. Performance was assessed using running times (5, 10, 20, 30 and 40 m), a sprint test with 180° turns (S180°), a 9-3-6-3-9 m sprint with backward and forward running (SBF), a 4 × 5 m sprint test with turns, repeated shuttle sprinting, repeated changes of direction, squat (SJ) and counter-movement (CMJ) jumping, back half-squatting, and a force-velocity test. Electromyographic (EMG) activity of the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) muscles was recorded during jumping. Two-way ANOVA showed significant gains in E relative to C during the straight sprint (all distances). Scores of E increased substantially (p ≤ 0.01) on S4 × 5 and SBF and moderately on S180°. Leg peak power, SJ, and CMJ were also enhanced, with significant increases in EMG activity. However, repeated-sprint parameters showed no significant changes. We conclude that biweekly strength training improves key components of performance in junior soccer players relative to standard in-season training.

Exercise-related sensations contribute to decrease power during repeated cycle sprints with limited influence on neural drive.

PURPOSES: We manipulated the inspired oxygen fraction (FiO2) to examine the effects of physiological perturbations on exercise-related sensations and the neural drive of the quadriceps during repeated, brief, maximal cycle sprints. METHODS: Nine active males completed a repeated sprint cycle protocol (10 × 4-s maximal sprints with 30 s of passive recovery) in normoxia (NM; FiO2 0.21) and severe normobaric hypoxia (HY; FiO2 0.13). Peak power, quadriceps Root Mean Squared electromyography (RMS EMG), physiological (heart rate, arterial oxygen saturation, blood lactate concentration) and perceptual responses were recorded. RESULTS: The 10 sprints in HY were associated with lower arterial oxygen saturation values compared to NM [80.7 ± 0.9 vs. 95.6 ± 0.6%; P < 0.001; effect size (ES) = 0.98], higher blood lactate values (11.9 ± 0.4 vs. 9.9 ± 0.9 mmol L-1; P = 0.05; ES = 0.36), and greater exercise-related sensations (~36%; P < 0.001; ES > 0.47). Mean power for sprints 1-10 were lower (-13 ± 3%; P = 0.001; ES = 0.79), and sprint decrement was more pronounced in HY compared to NM (21.4 ± 3.7 vs. 13.2 ± 2.7%; P = 0.003). There was a 17% decrease in RMS EMG activity from the first to the last sprint (P < 0.001; ES = 0.65), independent of condition (P = 0.597; ES = 0.04). CONCLUSIONS: Despite severe hypoxia exacerbating both physiological and perceptual perturbations, the performance decrement observed during the repeated sprint protocol did not coincide with an accentuated decline in RMS EMG activity. These data suggest that higher-than-normal exercise-related sensations or perceptions coincide with fatigue during repeated sprinting, independent of changes in neural drive, when the task characteristics are known beforehand.

Reliability of measures of quadriceps muscle function using magnetic stimulation.

INTRODUCTION: Magnetic stimulation can be used to assess muscle function by calculating voluntary activation using an interpolated twitch during maximal voluntary contractions (MVCs) and control twitches to potentiated muscle. In this study we assessed the reliability of torque, electromyography (EMG), and voluntary activation variables. METHODS: Fifteen men completed 5 testing sessions (2 familiarization and 3 reliability trials) to assess quadriceps femoris muscle function. Intra- and interday reliability levels of torque and EMG variables were estimated using typical error ± 90% confidence limits, expressed as percentage [coefficient of variation (CV)] and intraclass correlation coefficient. The smallest worthwhile change was calculated as 0.2 × between-participant standard deviation. RESULTS: Intra- and interday torque variables for MVC were reliable (CV < 4%, ICC 0.98, and CV < 5%, ICC 0.99, respectively). EMG variables were less reliable than torque variables, with CVs ranging from 7% to 18%. CONCLUSION: Magnetic stimulation of the femoral nerve is a reliable method for assessing muscle function.

Salbutamol effects on systemic potassium dynamics during and following intense continuous and intermittent exercise.

PURPOSE: Salbutamol inhalation is permissible by WADA in athletic competition for asthma management and affects potassium regulation, which is vital for muscle function. Salbutamol effects on arterial potassium concentration ([K+]a) during and after high-intensity continuous exercise (HIcont) and intermittent exercise comprising repeated, brief sprints (HIint), and on performance during HIint are unknown and were investigated. METHODS: Seven recreationally active men participated in a double-blind, randomised, cross-over design, inhaling 1000 µg salbutamol or placebo. Participants cycled continuously for 5 min at 40 % [Formula: see text]O2peak and 60 % [Formula: see text]O2peak, then HIcont (90 s at 130 % [Formula: see text]O2peak), 20 min recovery, and then HIint (3 sets, 5 × 4 s sprints), with 30 min recovery. RESULTS: Plasma [K+]a increased throughout exercise and subsequently declined below baseline (P < 0.001). Plasma [K+]a was greater during HIcont than HIint (P < 0.001, HIcont 5.94 ± 0.65 vs HIint set 1, 4.71 ± 0.40 mM); the change in [K+]a from baseline (Δ[K+]a) was 2.6-fold greater during HIcont than HIint (P < 0.001). The Δ[K+] throughout the trial was less with salbutamol than placebo (P < 0.001, treatment main effect, 0.03 ± 0.67 vs 0.22 ± 0.69 mM, respectively); and remained less after correction for fluid shifts (P < 0.001). The Δ[K+] during HIcont was less after salbutamol (P < 0.05), but not during HIint. Blood lactate, plasma pH, and the work output during HIint did not differ between trials. CONCLUSIONS: Inhaled salbutamol modulated the [K+]a rise across the trial, comprising intense continuous and intermittent exercise and recovery, lowering Δ[K+] during HIcont. The limited [K+]a changes during HIint suggest that salbutamol is unlikely to influence systemic [K+] during periods of intense effort in intermittent sports.

A Combination of Amino Acids and Caffeine Enhances Sprint Running Capacity in a Hot, Hypoxic Environment.

Heat and hypoxia exacerbate central nervous system (CNS) fatigue. We therefore investigated whether essential amino acid (EAA) and caffeine ingestion attenuates CNS fatigue in a simulated team sport-specific running protocol in a hot, hypoxic environment. Subelite male team sport athletes (n = 8) performed a repeat sprint running protocol on a nonmotorized treadmill in an extreme environment on 4 separate occasions. Participants ingested one of four supplements: a double placebo, 3 mg.kg-1 body mass of caffeine + placebo, 2 x 7 g EAA (Musashi Create)+placebo, or caffeine + EAA before each exercise session using a randomized, double-blind crossover design. Electromyography (EMG) activity and quadriceps evoked responses to magnetic stimulation were assessed from the dominant leg at preexercise, halftime, and postexercise. Central activation ratio (CAR) was used to quantify completeness of quadriceps activation. Oxygenation of the prefrontal cortex was measured via near-infrared spectroscopy. Mean sprint work was higher (M = 174 J, 95% CI [23, 324], p < .05, d = 0.30; effect size, likely beneficial) in the caffeine + EAA condition versus EAAs alone. The decline in EMG activity was less (M = 13%, 95% CI [0, 26]; p < .01, d = 0.58, likely beneficial) in caffeine + EAA versus EAA alone. Similarly, the pre- to postexercise decrement in CAR was significantly less (M = -2.7%, 95% CI [0.4, 5.4]; p < .05, d = 0.50, likely beneficial) when caffeine + EAA were ingested compared with placebo. Cerebral oxygenation was lower (M = -5.6%, 95% CI [1.0, 10.1]; p < .01, d = 0.60, very likely beneficial) in the caffeine + EAA condition compared with LNAA alone. Co-ingestion of caffeine and EAA appears to maintain muscle activation and central drive, with a small improvement in running performance.

Hot But Not Cold Water Immersion Mitigates the Decline in Rate of Force Development following Exercise-Induced Muscle Damage.

PURPOSE: In recent years, there has been significant advancement in the guidelines for recovery protocols involving heat or cold water immersion. Yet, comparison between the effects of hot and cold water immersion on key markers of neuromuscular recovery following exercise-induced muscle damage (EIMD) is lacking. METHODS: Thirty physically active males completed an individualized and tailored EIMD protocol immediately followed by one of the following recovery interventions: cold water immersion (11 °C, CWI11), hot water immersion (41 °C, HWI41) or warm-bath control (36 °C, CON36). Gastrointestinal temperature was tracked throughout HWI41. Knee extensors' maximal isokinetic strength [peak torque (Tpeak)] and explosive strength [late-phase rate of force development, (RFD100-200)] were measured prior to EIMD (pre-), 24 h (post-24 h) and 48 h (post-48 h) post-EIMD. In addition, pressure pain threshold (PPT) was measured to quantify the recovery from muscle soreness. Surface electromyography signals (sEMG) from the vastus lateralis were captured to extract the rates of electromyography rise (REMGR) and the spectral power in the low-frequency band. RESULTS: At post-48 h, Tpeak returned to baseline values following both CWI11 (-8.3 ± 6.8 %, p = 0.079) and HWI41 (-1.4 ± 4.1%, p = 1). In contrast, RFD100-200 (-2.3 ± 29.3%, p = 1) and PPT (+5.6 ± 14.6%, p = 1) returned to baseline values at post-48 h only following HWI41. Spectral analysis of the sEMG signal revealed that the low-frequency band was significantly increased following CWI11 (+9.0 ± 0.52%, p = 0.012). REMGR was unchanged regardless of the condition (all p > 0.05). CONCLUSIONS: A single session of HWI41, rather than CWI11, improved the recovery of the late-phase rate of force development following EIMD in physically active males. This suggests that in athletic contexts where a rapid force development is a key performance determinant, hot bath should be preferred over cold bath.