Reliability and validity of the MX3 portable sweat sodium analyser during exercise in warm conditions.

PURPOSE: Accurately measuring sweat sodium concentration ([Na+]) in the field is advantageous for coaches, scientists, and dieticians looking to tailor hydration strategies. The MX3 hydration testing system is a new portable analyser that uses pre-calibrated biosensors to measure sweat [Na+]. This study aimed to assess the validity and reliability of the MX3 hydration testing system. METHODS: Thirty-one (11 females) recreationally active participants completed one experimental trial. During this trial, participants exercised at a self-selected pace for 45 min in a warm environment (31.5 ± 0.8 °C, 63.2 ± 1.3% relative humidity). Sweat samples were collected from three measurement sites using absorbent patches. The samples were then analysed for sweat [Na+] using both the MX3 hydration testing system and the Horiba LAQUAtwin-NA-11. The reliability of the MX3 hydration testing system was determined following two measurements of the same sweat sample. RESULTS: The mean difference between measurements was 0.1 mmoL·L-1 (95% limits of agreement (LoA): - 9.2, 9.4). The analyser demonstrated a coefficient of variation (CV) of 5.6% and the standard error of measurement was 3.3 mmoL·L-1. When compared to the Horiba LAQUAtwin-NA-11, there was a mean difference of - 1.7 mmoL·L-1 (95% LoA: - 0.25 X ¯ , 0.25 X ¯ ) and the CV was 9.8%. CONCLUSION: The MX3 hydration testing system demonstrated very good single-trial reliability, moderate agreement and a very good CV relative to the Horiba LAQUAtwin-Na-11. To further validate its performance, the MX3 hydration testing system should be compared with analytical techniques known for superior reliability and validity.

Efficacy of the FIFA cooling break heat policy during an intermittent treadmill football simulation in hot conditions in trained males.

OBJECTIVE: To evaluate the efficacy of the Fédération Internationale de Football Association (FIFA) cooling break policy against alternative cooling configurations in attenuating thermal strain during simulated football in the heat. METHODS: 12 males (age: 27±6 years, V̇O2peak: 61±7 mL/kg/min) completed five 90 min intermittent treadmill football match simulations in 40°C and 41% relative humidity (32°C wet-bulb globe temperature) with different cooling configurations: regular match without cooling breaks (REG), 3 min breaks without cooling (BRKno-cool), 3 min breaks with cooling (BRKcool: current FIFA policy; chilled fluid ingestion and ice towel across neck and shoulders), 5 min extended half-time without cooling breaks (ExtHTonly) and 3 min cooling breaks with 5 min ExtHT (ExtHTcool). Rectal temperature (Tre), heart rate, whole-body sweat rate (WBSR) and rating of perceived exertion (RPE) were recorded. Data are presented as mean (95% CIs). RESULTS: Final Tre was lower in BRKno-cool (0.20°C (0.01, 0.39), p=0.038), BRKcool (0.39°C (0.21, 0.57), p<0.001) and ExtHTcool (0.40°C (0.22, 0.58), p<0.001) than REG (39.1°C (38.8, 39.3)). Mean Tre was lower in ExtHTcool (38.2°C (38.0, 38.4)) than BRKcool (38.3°C (38.1, 38.5), p=0.018), BRKno-cool and ExtHTonly (38.4°C (38.2, 38.6), p<0.001) and REG (38.5°C (38.3, 38.7), p<0.001). Mean heart rate was lower during BRKcool (6 beats/min (4, 7), p<0.001) and ExtHTcool (7 beats/min (6, 8), p<0.001) compared with REG. WBSR was comparable across trials (p≥0.07) and RPE was attenuated during BRKcool (0.4 (0.1, 0.7), p=0.004) and ExtHTcool (0.5 (0.2, 0.7), p=0.002), compared with REG. CONCLUSION: BRKcool and ExtHTcool attenuated thermal, cardiovascular and perceptual strain during a simulated football match in the heat. Additional strategies may be required in field settings or under harsher conditions.

Inter- and intra-athlete technique variability of conventional new ball swing bowling in elite and pre-elite Australian male fast bowlers.

This study aimed to investigate inter- and intra-athlete technique variability in pre-elite and elite Australian fast bowlers delivering new ball conventional swing bowling. Ball grip angle and pelvis, torso, shoulder, elbow, wrist, upper arm, forearm, and hand kinematics were investigated at the point of ball release for inswing and outswing deliveries. Descriptive evaluations of group and individual data and k-means cluster analyses were used to assess inter- and intra-bowler technique variability. Inter-athlete technique and ball grip variability were identified, demonstrating that skilled bowlers use individualised strategies to generate swing. Functional movement variability was demonstrated by intra-athlete variability in successful swing bowling trials. Bowlers demonstrated stable technique parameters in large proximal body segments of the pelvis and torso, providing a level of repeatability to their bowling action. Greater variation was observed in bowling arm kinematics, allowing athletes to manipulate the finger and ball position to achieve the desired seam orientation at the point of ball release. This study demonstrates that skilled bowlers use individualised techniques and grips to generate swing and employ technique variations in successive deliveries. Coaches should employ individualised training strategies and use constraints-led approaches in training environments to encourage bowlers to seek adaptive movement solutions to generate swing.

Bowler and coach experiential knowledge of new ball swing bowling in elite cricket.

Swing bowling can influence the outcome of cricket matches, but technique characteristics and coaching practices have not been investigated at an elite level. This study aimed to provide insight into the perceived technique parameters, coaching practices and variables contributing to conventional new ball swing bowling in elite cricket. Six Australian Test match fast bowlers and six Australian international and national-level coaches were interviewed. A reflexive thematic analysis of interview transcripts generated themes associated with swing bowling. Most bowlers reported their technique allows them to naturally create either inswing or outswing, with technique variations used to create swing in the opposite direction. To increase delivery effectiveness, bowlers and coaches recommended pitching the ball closer to the batter in length and varying release positions along the crease. Coaches recommended making individualised technique adjustments, but suggested all bowlers could benefit from maintaining balance and forward momentum to create a consistent release position in repeated deliveries. This study could inform training strategies to alter techniques and improve swing bowling performance. Future research should investigate the physical qualities of fast bowlers and use biomechanical analyses to provide a deeper understanding of swing bowling.

Rapid detection of isthmus block and rhythm change using local electrogram changes during complex atrial flutter ablation.

AIMS: Multiple re-entry circuits may operate simultaneously in the atria in the form of dual loop re-entry using a common isthmus, or multiple re-entrant loops without a common isthmus. When two or more re-entrant circuits coexist, ablation of an individual isthmus may lead to a seamless transition (without significant changes in surface electrocardiogram, coronary sinus activation or tachycardia cycle length) to a second rhythm, and the isthmus block can go unnoticed. METHODS AND RESULTS: We hypothesize and subsequently illustrate in three patient cases, methods to rapidly identify a transition in the rhythm and isthmus block using local electrogram changes at the ablation site. CONCLUSION: Local activation sequence changes, electrogram timing, and the behaviour of pre-existing double potentials can reveal isthmus block promptly when rhythm transitions occur during ablation of multiloop re-entry tachycardias.

The effect of α-lactalbumin consumption on sleep quality and quantity in female rugby union athletes: a field-based study.

This double-blind randomised placebo-controlled trial aimed to investigate the effects of α-lactalbumin consumption on sleep quality and quantity in female rugby union athletes during a competition season. Eighteen semi-professional female rugby union players (age 23.8 ± 5.2 y; mean ± SD) wore wrist actigraphy watches for four seven-day blocks corresponding to the pre-season, a home game, a bye week (i.e. no competition game scheduled) and an away game. Participants consumed either an α-lactalbumin (α-LAC), or placebo drink (PLA) every night two hours before bed for the duration of the season. Generalised linear mixed models were used to investigate the effects of the nutritional intervention on sleep variables (total sleep time, sleep efficiency (SE), sleep onset latency (SOL) and wake after sleep onset) over the duration of the season. There was a significant condition by period interaction effect on SOL (p = 0.01). While similar at baseline (23.3 ± 16.3 and 23.2 ± 18.9 min α-LAC and placebo respectively) and for the home game (22.4 ± 17.6 and 19.3 ± 14.9 min α-LAC and placebo respectively), SOL was reduced in the α-LAC group for the bye (11.6 ± 13.4 min) and away game (17.0 ± 11.5 min; p = 0.045). In comparison, SOL remained unchanged in the PLA group (bye 21.2 ± 17.3 and away 22.5 ± 18.5 min). Pre-sleep α-lactalbumin consumption improved SOL in a semi-professional female team-sport cohort. Thus, α-lactalbumin could be utilised by athletes to support sleep during a competitive season.

Influence of sex and biological maturation on the sudomotor response to exercise-heat stress: are girls disadvantaged?

Both adult females and children have been reported to have a lower sweating capacity and thus reduced evaporative heat loss potential that may increase their susceptibility to exertional hyperthermia in the heat. Compared with males, females have a lower maximal sweat rate and thus a theoretically lower maximum skin wettedness due to a lower sweat output per gland. Similarly, children have been suggested to be disadvantaged in high ambient temperatures due to a lower sweat production and therefore reduced evaporative capacity, despite modifications of heat transfer due to physical attributes and possible evaporative efficiency. The reported reductions in the sudomotor activity of females and children suggest a lower sweating capacity in girls. However, because of the complexities of isolating sex and maturation from the confounding effects of morphological differences (e.g., body surface area-to-mass ratio) and metabolic heat production, limited evidence exists supporting whether children, and, more specifically, girls are at a thermoregulatory disadvantage. Furthermore, a limited number of child-adult comparison studies involve females and very few studies have directly compared regional and whole body sudomotor activity between boys and girls. This minireview highlights the exercise-induced sudomotor response of females and children, summarizes previous research investigating the sudomotor response to exercise in girls, and suggests important areas for further research.

What are the sleep characteristics of elite female athletes? A systematic review with meta-analysis.

With the recent growth in female sport, practitioners need to be able to provide specific support to female athletes to ensure their sleep, health and athletic performance are optimised. Examine the patterns, duration and quality of sleep among elite female athletes, and consider the impact of situational challenges and their effects on the sleep of elite female athletes. Data was located through a search of SPORTDiscus, MEDLINE and Scopus from inception up to May 2021. Studies needed to be peer-reviewed research reporting quantitative sleep outcomes for female athletes ≥ 18 years of age and competing at a predefined elite level. A meta-analysis was performed on habitual sleep outcomes (e.g. total sleep time [TST] and sleep efficiency [SE]) measured with actigraphy. A total of 38 studies were included. Meta-analysis showed habitual TST (n = 14) was 7.8 h [7.4, 8.2] (mean [95% CI]), and SE was 86.7% [84.7, 88.6], with high variability among studies (I2 = 97.8-98.2%). Subjective sleep complaints are common before a competition, as do post-training sleep disturbances (63% studies report TST decrease), and post-competition sleep disturbances (75% studies report TST decrease). Female athletes achieve satisfactory objective sleep quantity and quality during habitual periods, but experience sleep disturbances pre- and post-situational challenges. There is high variability of objective sleep outcomes, demonstrating the individual nature of habitual female athlete sleep. Overall, future research must focus on optimising the sleep appraisal methods and creating high-quality study designs in a broader number of sports.

Novel approach to intracardiac defibrillator placement in patients with atriopulmonary Fontan: Ventricular defibrillation with an atrial positioned ICD lead.

INTRODUCTION: The Fontan procedure, used to palliate univentricular physiology, eliminates direct venous access to the ventricle and complicates implantable cardioverter-defibrillator (ICD) placement. METHODS AND RESULTS: We describe two patients with Fontan palliation who underwent a novel transvenous approach to ICD placement. The approach uses a transvenous bipolar lead placed in a coronary sinus branch for ventricular sensing, and a defibrillation lead placed in the right atrium for atrial sensing and ventricular defibrillation. CONCLUSION: Transvenous ICD implantation is possible in some patients with an atriopulmonary Fontan. This approach avoids a redo sternotomy for epicardial leads and excludes the need for lead placement in the systemic circulation.

Left atrial hypertension and the risk of early incident heart failure after atrial fibrillation ablation.

INTRODUCTION: Elevated left atrial pressure (LAP) during catheter ablation of atrial fibrillation (AF) is associated with an increased risk of AF recurrence, but it is unknown if this correlates with heart failure (HF). The objective of the study was to determine if elevated LAP after AF ablation correlates with HF events. METHODS: Prospective, single-center, cohort study measuring LAP and right atrial pressure (RAP) during AF ablation in 100 patients. The primary endpoint was clinical HF within 30 days of ablation. The secondary outcome was AF-free HF. RESULTS: One hundred patients (63% male, mean age 64.5) were enrolled and 20% had clinical HF within 30 days. Bivariate correlates included mitral valve (MV) disease, persistent AF, class III antiarrhythmics, LAP, and recurrent AF. Multivariate analysis revealed class III antiarrhythmics were protective (odds ratio [OR]: 0.24 [0.1-0.5], p = .04), while MV disease (OR: 8.7 [3.3-23], p = .03) and loop diuretics (OR: 4.8 [2.6-9.1], p = .01) were hazardous. AF-free HF occurred in 9% of patients and correlated with higher LAP and RAP, and chronic kidney disease. CONCLUSION: Patients with HF after AF ablation had higher LAP. MV disease, diuretic use, and class III antiarrhythmics also correlated to HF. These present opportunities to target future interventions to reduce a common complication of AF ablation.

Mechanism and interpretation of two-for-one response to premature atrial complexes during atrioventricular node re-entry tachycardia.

AIMS: The response to premature atrial complexes (PACs) during tachycardia has been shown to differentiate atrioventricular nodal re-entrant tachycardia (AVNRT) from focal junctional tachycardia (JT). His refractory PAC (HrPACs) perturbing the next His (resetting with fusion) is diagnostic of AVNRT and such a late PAC fusing with the native beat cannot reset the focal source of JT. Early PAC advancing the immediate His with continuation of tachycardia suggests JT but can also occur in AVNRT due to simultaneous conduction through the AV nodal fast and slow pathways [two-for-one response (TFOR)]. The objective of this study was to evaluate the incidence and mechanism of TFOR after early premature atrial complexes (ePACs) during AVNRT and to differentiate it from the known response to ePACs during JT. METHODS AND RESULTS: Typical AVNRT cases were diagnosed using standard criteria. We evaluated the responses to scanning PACs delivered during tachycardia in 100 patients undergoing AV node slow pathway modification for AVNRT. The responses to HrPACs and ePACs delivered from coronary sinus os or high right atrium were retrospectively reviewed. In 10 patients, ePACs advanced the immediate His with continuation of tachycardia. In all 10 cases, HrPACs advanced the next His, confirming AVNRT as the mechanism, and indicating a TFOR. CONCLUSION: A TFOR can occur in a small number of patients during AVNRT and is therefore not diagnostic of JT. However, HrPACs always perturbed the next His in these cases, confirming the diagnosis of AVNRT and allowing for differentiation from JT.

Quinine Ingestion During the Latter Stages of a 3,000-m Time Trial Fails to Improve Cycling Performance.

The ingestion of quinine, a bitter tastant, improves short-term (30 s) cycling performance, but it is unclear whether this effect can be integrated into the last effort of a longer race. The purpose of this study was to determine whether midtrial quinine ingestion improves 3,000-m cycling time-trial (TT) performance. Following three familiarization TTs, 12 well-trained male cyclists (mean ± SD: mass = 76.6 ± 9.2 kg, maximal aerobic power = 390 ± 50 W, maximal oxygen uptake = 4.7 ± 0.6 L/min) performed four experimental 3,000-m TTs on consecutive days. This double-blind, crossover design study had four randomized and counterbalanced conditions: (a) Quinine 1 (25-ml solution, 2 mM of quinine); (b) Quinine 2, replicate of Quinine 1; (c) a 25-ml sweet-tasting no-carbohydrate solution (Placebo); and (d) 25 ml of water (Control) consumed at the 1,850-m point of the TT. The participants completed a series of perceptual scales at the start and completion of all TTs, and the power output was monitored continuously throughout all trials. The power output for the last 1,000 m for all four conditions was similar: mean ± SD: Quinine 1 = 360 ± 63 W, Quinine 2 = 367 ± 63 W, Placebo = 364 ± 64 W, and Control = 367 ± 58 W. There were also no differences in the 3,000-m TT power output between conditions. The small perceptual differences between trials at specific 150-m splits were not explained by quinine intake. Ingesting 2 mM of quinine during the last stage of a 3,000-m TT did not improve cycling performance.

Predictors of successful ultrasound-guided lead implantation.

BACKGROUND: Technical advances have improved the safety of cardiac implantable electronic device (CIED) insertion, but periprocedural complications persist. Despite ultrasound (US) guidance for vascular access being feasible and exhibiting shorter fluoroscopy times, it is not widely adopted for insertion of CIEDs. Thus, we studied the use of US for CIED insertion to (1) quantify the success rate of venous cannulation, (2) identify predictors of failed cannulation, and (3) quantify the rate of complications using US guidance. METHODS: We studied 166 consecutive patients who underwent US-guided CIED implantation. Anatomic parameters of the axillary vein were measured. The primary outcome was success (group 1) or failure (group 2) to obtain vascular access utilizing US guidance. Secondary outcomes included pneumothorax and hematoma. RESULTS: Successful US-guided cannulation occurred in 154 of 166 patients (93%). No patient had a pneumothorax. Hematoma occurred in 1 of 166 patients (0.01%). Group 2 exhibited higher male proportion at 11 of 12 (92%) compared with 94 of 154 (61%) in group 1 (P = .03), increased vein depth at 3.84 versus 2.85 cm (P = .003), more right-sided implants (P = .03), higher weight at 104.6 versus 85.3 kg (P = .017), higher body mass index at 35.6 versus 29.2 kg/m2 (P = .049), and higher body surface area at 2.24 versus 1.99 m2 (P = .013). Other parameters were statistically nonsignificant. In multivariate analysis, vein depth remained significantly associated with failure. CONCLUSION: Using US guidance for CIED implantation is successful in the vast majority (93%) of patients. Rare cases of unsuccessful cannulation were associated with right-sided implants and increased venous depth.

Perceptions and use of recovery strategies: Do swimmers and coaches believe they are effective?

This study aimed to investigate swimmer's use and coach prescription of recovery strategies during training and competition while examining perceived challenges, barriers, and beliefs in the importance of their effectiveness. A mixed-methods sequential explanatory design was implemented. Thirty-seven male and 45 female sub-elite to elite swimmers (age 18 ± 3 y), and 4 male and 6 female coaches (age 40 ± 9 y) completed an online, 78-item recovery strategy survey. Swimmers and coaches responded to questions regarding when, why, and how they used recovery strategies, perceived challenges and barriers to strategy inclusion during training and competition. Data were coded and analysed thematically. Fisher's Exact Test was conducted on 5-point Likert scale responses. Most recovery strategies were used and prescribed more during competition. Swimmers reported active recovery as the most effective recovery strategy (44%), whereas coaches rated sleep or napping (40%). Swimmers and coaches perceived most recovery strategies to be more effective and important during competition than in training. Swimmers used, and coaches prescribed, recovery strategies more during the competition, highlighting the discrepancies in use between training and competition. Targeted education programmes should enhance athletes and coach's recovery knowledge and practical application of strategies, while accounting for individual sport and life demands.

Training Quantification and Periodization during Live High Train High at 2100 M in Elite Runners: An Observational Cohort Case Study.

The questionable efficacy of Live High Train High altitude training (LHTH) is compounded by minimal training quantification in many studies. We sought to quantify the training load (TL) periodization in a cohort of elite runners completing LHTH immediately prior to competition. Eight elite runners (6 males, 2 females) with a V̇O2peak of 70 ± 4 mL·kg-1·min-1 were monitored during 4 weeks of sea-level training, then 3-4 weeks LHTH in preparation for sea-level races following descent to sea-level. TL was calculated using the session rating of perceived exertion (sRPE) method, whereby duration of each training session was multiplied by its sRPE, then summated to give weekly TL. Performance was assessed in competition at sea-level before, and within 8 days of completing LHTH, with runners competing in 800 m (n = 1, 1500 m/mile (n = 6) and half-marathon (n = 1). Haemoglobin mass (Hbmass) via CO rebreathing and running economy (RE) were assessed pre and post LHTH. Weekly TL during the first 2 weeks at altitude increased by 75% from preceding sea-level training (p = 0.0004, d = 1.65). During the final week at altitude, TL was reduced by 43% compared to the previous weeks (p = 0.002; d = 1.85). The ratio of weekly TL to weekly training volume increased by 17% at altitude (p = 0.009; d = 0.91) compared to prior sea-level training. Hbmass increased by 5% from pre- to post-LHTH (p = 0.006, d = 0.20). Seven athletes achieved lifetime personal best performances within 8 days post-altitude (overall improvement 1.1 ± 0.7%, p = 0.2, d = 0.05). Specific periodization of training, including large increases in training load upon arrival to altitude (due to increased training volume and greater stress of training in hypoxia) and tapering, were observed during LHTH in elite runners prior to personal best performances. Periodization should be individualized and align with timing of competition post-altitude.

Quantifying Exercise Heat Acclimatisation in Athletes and Military Personnel: A Systematic Review and Meta-analysis.

BACKGROUND: Athletes and military personnel are often expected to compete and work in hot and/or humid environments, where decrements in performance and an increased risk of exertional heat illness are prevalent. A physiological strategy for reducing the adverse effects of heat stress is to acclimatise to the heat. OBJECTIVE: The aim of this systematic review was to quantify the effects of relocating to a hotter climate to undergo heat acclimatisation in athletes and military personnel. ELIGIBILITY CRITERIA: Studies investigating the effects of heat acclimatisation in non-acclimatised athletes and military personnel via relocation to a hot climate for < 6 weeks were included. DATA SOURCES: MEDLINE, SPORTDiscus, CINAHL Plus with Full Text and Scopus were searched from inception to June 2022. RISK OF BIAS: A modified version of the McMaster critical review form was utilised independently by two authors to assess the risk of bias. DATA SYNTHESIS: A Bayesian multi-level meta-analysis was conducted on five outcome measures, including resting core temperature and heart rate, the change in core temperature and heart rate during a heat response test and sweat rate. Wet-bulb globe temperature (WBGT), daily training duration and protocol length were used as predictor variables. Along with posterior means and 90% credible intervals (CrI), the probability of direction (Pd) was calculated. RESULTS: Eighteen articles from twelve independent studies were included. Fourteen articles (nine studies) provided data for the meta-analyses. Whilst accounting for WBGT, daily training duration and protocol length, population estimates indicated a reduction in resting core temperature and heart rate of - 0.19 °C [90% CrI: - 0.41 to 0.05, Pd = 91%] and - 6 beats·min-1 [90% CrI: - 16 to 5, Pd = 83%], respectively. Furthermore, the rise in core temperature and heart rate during a heat response test were attenuated by - 0.24 °C [90% CrI: - 0.67 to 0.20, Pd = 85%] and - 7 beats·min-1 [90% CrI: - 18 to 4, Pd = 87%]. Changes in sweat rate were conflicting (0.01 L·h-1 [90% CrI: - 0.38 to 0.40, Pd = 53%]), primarily due to two studies demonstrating a reduction in sweat rate following heat acclimatisation. CONCLUSIONS: Data from athletes and military personnel relocating to a hotter climate were consistent with a reduction in resting core temperature and heart rate, in addition to an attenuated rise in core temperature and heart rate during an exercise-based heat response test. An increase in sweat rate is also attainable, with the extent of these adaptations dependent on WBGT, daily training duration and protocol length. PROSPERO REGISTRATION: CRD42022337761.

Influence of Biological Sex and Fitness on Core Temperature Change and Sweating in Children Exercising in Warm Conditions.

PURPOSE: This study aimed to investigate the associations of biological sex and aerobic fitness (i.e., V̇O 2peak ) on the change in gastrointestinal temperature (∆ Tgi ) and whole-body sweat rate (WBSR) of children exercising in warm conditions. METHODS: Thirty-eight children (17 boys, mean ± SD = 13.7 ± 1.2 yr; 21 girls, 13.6 ± 1.8 yr) walked for 45 min at a fixed rate of metabolic heat production (8 W·kg -1 ) in 30°C and 40% relative humidity. Biological sex and relative V̇O 2peak were entered as predictors into a Bayesian hierarchical generalized additive model for Tgi . For a subsample of 13 girls with measured body composition, body fat percent was entered into a separate hierarchical generalized additive model for Tgi . Sex, V̇O 2peak , and the evaporative requirement for heat balance ( Ereq ) were entered into a Bayesian hierarchical linear regression for WBSR. RESULTS: The mean ∆ Tgi for boys was 0.71°C (90% credible interval = 0.60-0.82) and for girls 0.78°C (0.68-0.88). A predicted 20 mL·kg -1 ·min -1 higher V̇O 2peak resulted in a 0.19°C (-0.03 to 0.43) and 0.24°C (0.07-0.40) lower ∆ Tgi in boys and girls, respectively. A predicted ~13% lower body fat in the subsample of girls resulted in a 0.15°C (-0.12 to 0.45) lower ∆ Tgi . When Ereq was standardized to the grand mean, the difference in WBSR between boys and girls was -0.00 L·h -1 (-0.06 to 0.06), and a 20-mL·kg -1 ·min -1 higher predicted V̇O 2peak resulted in a mean difference in WBSR of -0.07 L·h -1 (-0.15 to 0.00). CONCLUSIONS: Biological sex did not independently influence ∆ Tgi and WBSR in children. However, a higher predicted V̇O 2peak resulted in a lower ∆ Tgi of children, which was not associated with a greater WBSR, but may be related to differences in body fat percent between high and low fitness individuals.

Biological sex does not independently influence core temperature change and sweating of children exercising in uncompensable heat stress.

The purpose of this study was to investigate the influence of biological sex, independent of differences in aerobic fitness and body fatness, on the change in gastrointestinal temperature (ΔTgi) and whole body sweat rate (WBSR) of children exercising under uncompensable heat stress. Seventeen boys (means ± SD; 13.7 ± 1.3 yr) and 18 girls (13.7 ± 1.4 yr) walked for 45 min at a fixed rate of metabolic heat production per kg body mass (8 W·kg-1) in 40°C and 30% relative humidity. Sex and peak oxygen consumption (V̇o2peak) were entered into a Bayesian hierarchical general additive model (HGAM) for Tgi. Sex, V̇o2peak, and the evaporative requirement for heat balance (Ereq) were entered into a Bayesian hierarchical linear regression for WBSR. For 26 (12 M and 14 F) of the 35 children with measured body composition, body fat percentage was entered in a separate HGAM and hierarchical linear regression for Tgi and WBSR, respectively. Conditional on sex-specific mean V̇o2peak, ΔTgi was 1.00°C [90% credible intervals (Crl): 0.84, 1.16] for boys and 1.17°C [1.01, 1.33] for girls, with a difference of 0.17°C [-0.39, 0.06]. When sex differences in V̇o2peak were accounted for, the difference in ΔTgi between boys and girls was 0.01°C [-0.25, 0.22]. The difference in WBSR between boys and girls was 0.03 L·h-1 [-0.02, 0.07], when isolated from differences in Ereq. The difference in ΔTgi between boys and girls was -0.10°C [-0.38, 0.17] when sex differences in body fat (%) were accounted for. Biological sex did not independently influence the ΔTgi and WBSR of children exercising under uncompensable heat stress.NEW & NOTEWORTHY Limited studies have investigated the thermoregulatory responses of boys and girls exercising under uncompensable heat stress. Boys and girls often differ in physiological characteristics other than biological sex, such as aerobic fitness and body fat percentage, which may confound interpretations. We investigated the influence of biological sex on exercise thermoregulation in children, independent of differences in aerobic fitness and body fatness.