The effect of 8-day oral taurine supplementation on thermoregulation during low-intensity exercise at fixed heat production in hot conditions of incremental humidity.

PURPOSE: To determine the effect of taurine supplementation on sweating and core temperature responses, including the transition from compensable to uncompensable heat stress, during prolonged low-intensity exercise of a fixed-heat production (~ 200W/m2) in hot conditions (37.5 °C), at both fixed and incremental vapour-pressure. METHODS: Fifteen females (n = 3) and males (n = 12; 27 ± 5 years, 78 ± 9 kg, V ˙ O2max 50.3 ± 7.8 mL/kg/min), completed a treadmill walking protocol (~ 200W/m2 heat production [Hprod]) in the heat (37.5 ± 0.1 °C) at fixed-(16-mmHg) and ramped-humidity (∆1.5-mmHg/5-min) following 1 week of oral taurine supplementation (50 mg/kg/bm) or placebo, in a double-blind, randomised, cross-over design. Participants were assessed for whole-body sweat loss (WBSL), local sweat rate (LSR), sweat gland activation (SGA), core temperature (Tcore), breakpoint of compensability (Pcrit) and calorimetric heat transfer components. Plasma volume and plasma taurine concentrations were established through pre- and post-trial blood samples. RESULTS: Taurine supplementation increased WBSL by 26.6% and 5.1% (p = 0.035), LSR by 15.5% and 7.8% (p = 0.013), SGA (1 × 1 cm) by 32.2% and 29.9% (p < 0.001) and SGA (3 × 3 cm) by 22.1% and 17.1% (p = 0.015) during the fixed- and ramped-humidity exercise periods, respectively. Evaporative heat loss was enhanced by 27% (p = 0.010), heat-storage reduced by 72% (p = 0.024) and Pcrit was greater in taurine vs placebo (25.0-mmHg vs 21.7-mmHg; p = 0.002). CONCLUSION: Taurine supplementation increased sweating responses during fixed Hprod in hot conditions, prior to substantial heat strain and before the breakpoint of compensability, demonstrating improved thermoregulatory capacity. The enhanced evaporative cooling and reduced heat-storage delayed the subsequent upward inflection in Tcore-represented by a greater Pcrit-and offers a potential dietary supplementation strategy to support thermoregulation.

Mental Rehearsal Improves Passing Skill and Stress Resilience in Rugby Players.

PURPOSE: Mental rehearsal is commonly employed, with positive visualization proposed to enhance complex skill performance. Additionally, video stimulus has been associated with enhanced kinesthetic sensations and rapid hormone fluctuations that may contribute to enhancing mental rehearsal and the conscious and unconscious emotional state for skill execution. Here, we assessed the impact of a 15-minute mental rehearsal intervention on rugby-specific tasks and the associated hormone profile. METHODS: Professional rugby players (N = 10) volunteered for a randomized crossover study. They completed three 15-minute preparatory phases (positive or negative video-guided mental rehearsal or self-directed mental rehearsal alone) prior to an exercise stressor and rugby-specific passing task. Salivary testosterone and cortisol were monitored to assess stress responses. RESULTS: Performance during the rugby passing task was improved following the positive video condition (91% [7.4%]) compared to the negative video (79% [6.0%]; ES: 1.22 ± 0.75) and self-visualization (86% [5.8%]; ES: 0.58 ± 0.75), with a significant correlation observed between passing performance and salivary testosterone (r = .47 ± .34, P = .0087). Positive video imagery prior to an exercise stressor also significantly enhanced physiological stress resilience (r = .39 ± .36, P = .0352). CONCLUSIONS: This pilot study demonstrates that mental rehearsal was enhanced by appropriate, context-specific video presentation. We propose that the interaction between sex steroids, the adrenal axis, and subsequent conscious and unconscious behaviors may be relevant to competitive rugby. Specifically, we suggest that relatively elevated free testosterone imparts a degree of stress resilience, which may lead to enhanced expression of competitive behaviors and provide an enhanced state for rugby skill execution.

The Effect of Dietary Supplements on Endurance Exercise Performance and Core Temperature in Hot Environments: A Meta-analysis and Meta-regression.

BACKGROUND: The ergogenic effects of dietary supplements on endurance exercise performance are well-established; however, their efficacy in hot environmental conditions has not been systematically evaluated. OBJECTIVES: (1) To meta-analyse studies investigating the effects of selected dietary supplements on endurance performance and core temperature responses in the heat. Supplements were included if they were deemed to: (a) have a strong evidence base for 'directly' improving thermoneutral endurance performance, based on current position statements, or (b) have a proposed mechanism of action that related to modifiable factors associated with thermal balance. (2) To conduct meta-regressions to evaluate the moderating effect of selected variables on endurance performance and core temperature responses in the heat following dietary supplementation. METHODS: A search was performed using various databases in May 2020. After screening, 25 peer-reviewed articles were identified for inclusion, across three separate meta-analyses: (1) exercise performance; (2) end core temperature; (3) submaximal core temperature. The moderating effect of several variables were assessed via sub-analysis and meta-regression. RESULTS: Overall, dietary supplementation had a trivial significant positive effect on exercise performance (Hedges' g = 0.18, 95% CI 0.007-0.352, P = 0.042), a trivial non-significant positive effect on submaximal core temperature (Hedges' g = 0.18, 95% CI - 0.021 to 0.379, P = 0.080) and a small non-significant positive effect on end core temperature (Hedges' g = 0.20, 95% CI - 0.041 to 0.439, P = 0.104) in the heat. There was a non-significant effect of individual supplements on exercise performance (P = 0.973) and submaximal core temperature (P = 0.599). However, end core temperature was significantly affected by supplement type (P = 0.003), which was attributable to caffeine's large significant positive effect (n = 8; Hedges' g = 0.82, 95% CI 0.433-1.202, P < 0.001) and taurine's medium significant negative effect (n = 1; Hedges' g = - 0.96, 95% CI - 1.855 to - 0.069, P = 0.035). CONCLUSION: Supplements such as caffeine and nitrates do not enhance endurance performance in the heat, with caffeine also increasing core temperature responses. Some amino acids might offer the greatest performance benefits in the heat. Exercising in the heat negatively affected the efficacy of many dietary supplements, indicating that further research is needed and current guidelines for performance in hot environments likely require revision.

Abbreviated Resonant Frequency Training to Augment Heart Rate Variability and Enhance On-Demand Emotional Regulation in Elite Sport Support Staff.

Support and management staff in elite sport experience work-related stress and emotional disturbance to a similar extent as athletes (Fletcher and Wagstaff 2009). The resonant frequency breathing technique (Lehrer et al. 2000) can inhibit autonomic changes associated with stressful situations or events and as such provides a potential emotional regulation tool. The present study utilised five practitioner-led heart rate variability (HRV) biofeedback sessions and home practice via mobile applications to train support and management staff (n = 9) in resonant frequency breathing techniques. Although baseline HRV did not change from pre to post training, participants increased total HRV (i.e., SDNN; p = .006), parasympathetic HRV (i.e., RMSSD; p = .028) and HRV reflective of baroreflex function (i.e., low frequency power; p = .018) while accurately performing resonant frequency breathing without a breath pacer. Post-intervention questionnaire data revealed an increase (p = .032) in habitual use of somatic strategies for emotional regulation, and social validation data suggested that the technique enhanced emotional regulation at home, work and during international competition. HRV biofeedback and the resonant frequency technique provided an on-demand emotional regulation technique for elite sport support and management staff.

Physiological and performance effects of carbohydrate gels consumed prior to the extra-time period of prolonged simulated soccer match-play.

OBJECTIVES: The physiological and performance effects of carbohydrate-electrolyte gels consumed before the 30min extra-time period of prolonged soccer-specific exercise were investigated. DESIGN: Randomised, double-blind, crossover. METHODS: Eight English Premier League academy soccer players performed 120min of soccer-specific exercise on two occasions while consuming fluid-electrolyte beverages before exercise, at half-time and 90min. Carbohydrate-electrolyte (0.7±0.1gkg(-1) BM) or energy-free placebo gels were consumed ∼5min before extra-time. Blood samples were taken before exercise, at half-time and every 15min during exercise. Physical (15-m and 30-m sprint speed, 30-m sprint maintenance and countermovement jump height) and technical (soccer dribbling) performance was assessed throughout each trial. RESULTS: Carbohydrate-electrolyte gels improved dribbling precision (+29±20%) and raised blood glucose concentrations by 0.7±0.8mmoll(-1) during extra-time (both p<0.01). Supplementation did not affect sprint velocities (15m and 30m), 30-m sprint maintenance or dribbling speed as reductions compared to 0-15min values occurred at 105-120min irrespective of trial (all p<0.05). Plasma osmolality and blood sodium concentrations increased post-exercise vs. the opening 15min (p<0.05) but no effect of supplementation existed. Selected markers of physical performance (jump height, 30-m sprint velocity and 30-m repeated sprint maintenance) also reduced by >3% during half-time (all p<0.05). CONCLUSIONS: Carbohydrate-electrolyte gel ingestion raised blood glucose concentrations and improved dribbling performance during the extra-time period of simulated soccer match-play. Supplementation did not attenuate reductions in physical performance and hydration status that occurred during extra-time.

The impact of neuromuscular electrical stimulation on recovery after intensive, muscle damaging, maximal speed training in professional team sports players.

OBJECTIVES: During congested fixture periods in team sports, limited recovery time and increased travel hinder the implementation of many recovery strategies; thus alternative methods are required. We examined the impact of a neuromuscular electrical stimulation device on 24-h recovery from an intensive training session in professional players. DESIGN: Twenty-eight professional rugby and football academy players completed this randomised and counter-balanced study, on 2 occasions, separated by 7 days. METHODS: After baseline perceived soreness, blood (lactate and creatine kinase) and saliva (testosterone and cortisol) samples were collected, players completed a standardised warm-up and baseline countermovement jumps (jump height). Players then completed 60 m × 50 m maximal sprints, with 5 min recovery between efforts. After completing the sprint session, players wore a neuromuscular electrical stimulation device or remained in normal attire (CON) for 8 h. All measures were repeated immediately, 2 and 24-h post-sprint. RESULTS: Player jump height was reduced from baseline at all time points under both conditions; however, at 24-h neuromuscular electrical stimulation was significantly more recovered (mean±SD; neuromuscular electrical stimulation -3.2±3.2 vs. CON -7.2±3.7%; P<0.001). Creatine kinase concentrations increased at all time points under both conditions, but at 24-h was lower under neuromuscular electrical stimulation (P<0.001). At 24-h, perceived soreness was significantly lower under neuromuscular electrical stimulation, when compared to CON (P=0.02). There was no effect of condition on blood lactate, or saliva testosterone and cortisol responses (P>0.05). CONCLUSIONS: Neuromuscular electrical stimulation improves recovery from intensive training in professional team sports players. This strategy offers an easily applied recovery strategy which may have particular application during sleep and travel.

Electrostimulation's enhancement of recovery during a rugby preseason.

UNLABELLED: Rugby preseason training involves high-volume strength and conditioning training, necessitating effective management of the recovery-stress state to avoid overtraining and maximize adaptive gains. PURPOSE: Compression garments and an electrostimulation device have been proposed to improve recovery by increasing venous blood flow. These devices were assessed using salivary testosterone and cortisol, plasma creatine kinase, and player questionnaires to determine sleep quality, energy level, mood, and enthusiasm. METHODS: Twenty-five professional rugby players were assigned to 1 of 2 treatments (compression garment or a concurrent combination of electrostimulation and compression) in a crossover design over 2 × 2-wk training blocks. RESULTS: Substantial benefits were observed in self-assessed energy levels (effect size [ES] 0.86), and enthusiasm (ES 0.80) as a result of the combined treatment when compared with compression-garment use. The combination treatment had no discernable effect on salivary hormones, with no treatment effect observed. The electrostimulation device did tend to accelerate the return of creatine kinase to baseline levels after 2 preseason rugby games when compared with the compression-garment intervention (ES 0.61; P = .08). CONCLUSIONS: Electrostimulation elicited psychometric and physiological benefits reflective of an improved recovery-stress state in professional male rugby players when combined with a lower-body compression garment.

Role of creatine supplementation on exercise-induced cardiovascular function and oxidative stress.

Many degenerative diseases are associated with increased oxidative stress. Creatine has the potential to act as an indirect and direct antioxidant; however, limited data exist to evaluate the antioxidant capabilities of creatine supplementation within in-vivo human systems. This study aimed to investigate the effects of oral creatine supplementation on markers of oxidative stress and antioxidant defenses following exhaustive cycling exercise. Following preliminary testing and two additional familiarization sessions, 18 active males repeated two exhaustive incremental cycling trials (T1 and T2) separated by exactly 7 days. The subjects were assigned, in a double-blind manner, to receive either 20 g of creatine (Cr) or a placebo (P) for the 5 days preceding T2. Breath-by-breath respiratory data and heart rate were continually recorded throughout the exercise protocol and blood samples were obtained at rest (preexercise), at the end of exercise (postexercise), and the day following exercise (post24 h). Serum hypdroperoxide concentrations were elevated at postexercise by 17 +/- 5% above pre-exercise values (P = 0.030). However, supplementation did not influence lipid peroxidation (serum hypdroperoxide concentrations), resistance of low density lipoprotein to oxidative stress (t1/2max LDL oxidation) and plasma concentrations of non-enzymatic antioxidants (retinol, alpha-carotene, beta-carotene, alpha-tocopherol, gamma-tocopherol, lycopene, and vitamin C). Heart rate and oxygen uptake responses to exercise were not affected by supplementation. These findings suggest that short-term creatine supplementation does not enhance non-enzymatic antioxidant defence or protect against lipid peroxidation induced by exhaustive cycling in healthy males.

Phosphatidylserine supplementation and recovery following downhill running.

PURPOSE: This study investigated the effects of 750 mg of soybean-derived phosphatidylserine (S-PtdSer), administered daily for 7 d prior to a bout of eccentric exercise and for 2d following exercise, on delayed onset of muscle soreness and markers of muscle damage, inflammation, and oxidative stress that followed prolonged downhill running. METHODS: Following preliminary testing and a familiarization session, eight recreationally active males repeated an individualized downhill run at -16.5% for 51.0 +/- 1.5 min at 8.7 +/- 0.3 km x h(-1) on four occasions (trials 1-4). Trials 1 and 37 were presupplementation control trials. After trials 1 and 3 the subjects received, in a double-blind and crossover fashion, either S-PtdSer or a glucose polymer placebo. Trials 2 and 3 were separated by a 4-wk washout period. Venous blood, perceived soreness ratings, and feeling states were assessed prior to exercise, after exercise, and at 24 and 48 h after exercise during each trial. RESULTS: Downhill running led to elevations in perceived soreness (P < 0.05), creatine kinase activities (P < 0.001), myoglobin concentrations (P < 0.001), interleukin-6 (IL-6) concentrations (P < 0.001), and lipid hydroperoxide concentrations (P < 0.01). However, supplementation did not significantly attenuate these responses. CONCLUSION: These results suggest that supplementation with 750 mg x d(-1) S-PtdSer for 10 d does not afford additional protection against delayed onset of muscle soreness and markers of muscle damage, inflammation, and oxidative stress that follow prolonged downhill running.

Effects of phosphatidylserine on exercise capacity during cycling in active males.

PURPOSE: The purpose of the study was to investigate the effects of 750 mg of soybean-derived phosphatidylserine, administered daily for 10 d, on exercise capacity, oxygen uptake kinetic response, neuroendocrine function, and feeling states during exhaustive intermittent exercise. METHODS: Following preliminary testing, fourteen active males completed a staged intermittent exercise protocol on two further occasions (T1 and T2) separated by 16 +/- 1 d. The protocol consisted of three 10-min stages of cycling at 45, 55, and 65% VO2max, followed by a final bout at 85% VO2max that was continued until exhaustion. Approximately 5 d after T1 the subjects were assigned, in a double-blind manner, to either phosphatidylserine (PS) or placebo (P). Breath-by-breath respiratory data and heart rate were continually recorded throughout the exercise protocol, and blood samples were obtained at rest, during the rest periods within the protocol (Post-55, Post-65), at the end of exercise (Post-85), 20 min after the completion of exercise (postexercise), and the day following exercise (Post-24 h). RESULTS: The main finding of this study was that supplementation had a significant effect on exercise time to exhaustion at 85% VO2max (P = 0.005). The exercise time to exhaustion in PS increased following supplementation (7:51 +/- 1:36 to 9:51 +/- 1:42 min:s, P = 0.001), whereas P remained unchanged (8:09 +/- 0:54 to 8:02 +/- 0:54 min:s, P = 0.670). Supplementation did not significantly affect oxygen kinetic mean response times (MRT(on) and MRT(off)), serum cortisol concentrations, substrate oxidation, and feeling states during the trial. CONCLUSION: This is the first study to report improved exercise capacity following phosphatidylserine supplementation. These findings suggest that phosphatidylserine might possess potential ergogenic properties.

Effects of phosphatidylserine on oxidative stress following intermittent running.

PURPOSE: The aim of the study was to investigate the effects of 750 mg of soybean-derived phosphatidylserine or a glucose polymer placebo, administered daily for 10 d, on markers of oxidative stress, perceived soreness, and muscle damage initiated by intermittent exercise (designed to simulated soccer match play) immediately followed by an exhaustive run. METHODS: Following familiarization, 16 male soccer players completed an exhaustive intermittent exercise protocol on two further occasions (T1 and T2) separated by approximately 14 d. Ten days before T2, the subjects were assigned, in a double-blind manner, to receive either phosphatidylserine (PS) or a placebo (P). Exercise time to exhaustion, sprint performance, ratings of perceived exertion, and HR were recorded throughout both main exercise trials. Venous blood samples were obtained at rest (preexercise), 15 min following exercise (postexercise), 24 h after exercise (post-24 h), and 48 h after exercise (post-48 h). RESULTS: Preexercise and postexercise concentrations of plasma gamma-tocopherol were increased following supplementation in PS, although supplementation had no effect on plasma concentrations of other nonenzymatic antioxidants (vitamin C, alpha-tocopherol, retinol, and beta-carotene). Serum cortisol concentrations, perceived soreness, markers of muscle damage (creatine kinase (CK) and myoglobin (Mb)), and lipid peroxidation (hydroperoxides and conjugated diene lag times) were elevated to an equal extent in PS and P following exhaustive exercise before and following supplementation. The changes in running times to exhaustion from T1 to T2 in PS and P were 4.2 +/- 0.7 and -3.7 +/- 4.2%, respectively (P = 0.084). CONCLUSION: Supplementation with phosphatidylserine was not effective in attenuating the cortisol response, perceived soreness, and markers of muscle damage and lipid peroxidation following exhaustive running; however, supplementation tended to increase running time to exhaustion. Therefore, future research should be undertaken to investigate the potential ergogenic properties of this supplement.

Effects of creatine on isometric bench-press performance in resistance-trained humans.

PURPOSE: The purpose of this study was to investigate the effects of creatine (Cr) supplementation on force generation during an isometric bench-press in resistance-trained men. METHODS: 32 resistance-trained men were matched for peak isometric force and assigned in double-blind fashion to either a Cr or placebo group. Subjects performed an isometric bench-press test involving five maximal isometric contractions before and after 5 d of Cr (20 g.d-1 Cr + 180 g.d-1 dextrose) or placebo (200 g.d-1 dextrose). Body composition was measured before and after supplementation. Subjects completed 24-h urine collections throughout the study period; these were subsequently analyzed to provide total Cr and creatinine excretion. RESULTS: The amount of Cr retained over the supplementation period was 45 +/- 18 g (mean +/- SD), with an estimated intramuscular Cr storage of 43 (13-61) mmol x kg(-1) x dry weight muscle (median [range]). Four subjects in the Cr group were classified as "nonresponders" (< or =21 mmol x kg(-1) x dry weight muscle increase following Cr supplementation) and the remaining 17 subjects were classed as "responders" (> or =32 mmol x kg(-1) x dry weight muscle). For the Cr group, peak force and total force pre- or post-supplementation were not different from placebo. However, when the analysis was confined to the responders, both the change in peak force [Repetition 2: 59(81) N vs -26(85) N; Repetition 3: 45(59) N vs -26(64) N) and the change in total force (Repetition 1: 1471(1274) N vs 209(1517) N; Repetition 2: 1575(1254) N vs 196(1413) N; Repetition 3: 1278(1245) N vs -3(1118) N; Repetition 4: 918(935) N vs -83(1095) N] post-supplementation were significantly greater compared with the placebo group (P < 0.01). For the Cr group, estimated Cr uptake was inversely correlated with training status (r = -0.68, N = 21, P = 0.001). Cr significantly increased body weight (84.1 +/- 8.6 kg pre- vs 85.3 +/- 8.3 kg post-supplementation) and fat-free mass (71.8 +/- 6.0 kg pre- vs 72.6 +/- 6.0 kg post-supplementation), with the magnitude of increase being significantly greater in the responder group than in the placebo group. CONCLUSION: Five days of Cr supplementation increased body weight and fat-free body mass in resistance-trained men who were classified as responders. Peak force and total force during a repeated maximal isometric bench-press test were also significantly greater in the responders compared to the placebo group.