ECSS Paris 2023: OP-PN05
INTRODUCTION: Global warming and rising ambient temperatures pose significant challenges for outdoor sports, including football, by increasing the physiological risks associated with heat stress. Female referees are exposed to the same environmental challenges as football players; however, they are often overlooked, and their physiological response to exercise in the heat remains unknown. This study aimed to assess the effects of exercising in hot and humid (HEAT) compared to temperate (TEMP) conditions on the core temperature (Tc) and hydration status of female football referees. METHODS: Twelve female football referees (27.9 ± 5.1 y, Tier 3), users (n = 8) and non-users (n = 4) of hormonal contraceptives, performed a 90-minute exercise protocol with two 45-minute halves separated by a 15-minute break (SAFT90) in HEAT (ambient temperature [Ta], 31ºC; relative humidity [RH], 74%; Wet Bulb Globe Temperature [WBGT], 28ºC) and TEMP (22ºC Ta; 65% RH; 19ºC WBGT). The study had a randomised, crossover design and was conducted indoors. Menstrual cycle and hormonal contraceptive use were tracked. Users of hormonal contraceptives were tested during the taking phase, while naturally menstruating participants were mostly tested during the luteal phase. Tc was recorded continuously via ingestible telemetric capsules (BodyCAP). Hydration status was assessed by urine specific gravity (USG), saliva osmolality (SOSM), body mass loss, sweat rate, and sweat sodium concentration [Na+]. Four participants did not complete the study due to knee pain (n = 2) or not tolerating the humid heat (n = 2). Their available data were included in the analysis. Data were analysed using linear mixed-effects models and are presented as mean and 95% confidence intervals. RESULTS: The participants started both exercise sessions in a euhydrated state (USG: 1.012 ± 0.006; SOSM: 64.6 ± 12.3 mOsm). During exercise, the peak Tc reached was higher in HEAT (39.0ºC [38.7, 39.2] vs 38.5ºC [38.2, 38.9]; p = .006). A Tc value of 39.0ºC was reached or exceeded by two participants in TEMP and by eight in HEAT. Overall, the peak Tc was 39.3ºC among those who fully completed the study and 39.5ºC among those who did not. Peak values were mainly reached during the first half (between minutes 17 and 47), except for two participants in HEAT (minutes 85 and 95). The mean Tc values (38.3ºC [38.1, 38.6] vs 38.0ºC [37.8, 38.2]; p = .017) and the sweat rate (0.9 L/h [0.7, 1.0] vs 0.6 L/h [0.6, 0.7]; p = .004) were both higher in HEAT. Neither body mass loss (HEAT: 1.1% [0.8, 1.4] vs TEMP: 1.2% [1.0, 1.5]; p = .558) nor saliva osmolarity (HEAT: 92.8 [80.2, 105.4] vs TEMP: 94.3 [78.5, 110.0]; p = 1.000) differed between conditions. Similarly, the sweat [Na+] was not impacted by HEAT (HEAT: 36.6 mmol/L [24.5, 48.6] vs TEMP: 32.8 mmol/L [17.7, 48.0]; p = .387). CONCLUSION: Exposure to hot and humid conditions during a 90-minute exercise protocol increased both thermal strain and sweat rate in female football referees relative to temperate conditions.
Read CV Catarina Batista OliveiraECSS Paris 2023: OP-PN05
INTRODUCTION: Exercise-associated muscle cramps (EAMCs) can have race-ruining consequences for endurance athletes, though the relevance of sodium (Na+) loss to cramp risk remains debated. Previous laboratory and field studies reporting no differences in serum [Na+] between athletes who do and do not experience cramp have contributed to the view that electrolyte disturbance is not a key factor in cramp risk. However, serum [Na+] is tightly regulated, potentially obscuring meaningful inter-individual differences in Na+ loss during prolonged endurance exercise. Consequently, the relationship between sweat [Na+] and EAMC risk remains insufficiently characterised in large, real-world athlete populations. We, therefore, aimed to examine the association between sweat [Na+] and EAMC frequency, and to provide normative sweat [Na+] across a diverse population. METHODS: Sweat [Na+] and self-reported EAMC frequency data from 24,498 athletes (men: 18,924; women: 4,963; prefer not to say: 611) undergoing standardised sweat testing were analysed. Associations were assessed using the Kruskal-Wallis H test and ordinal logistic regression. Secondary analyses on a larger cohort (n = 29,835) across 32,249 individual tests examined relationships between sweat [Na+] and interactions with sex, age, competitive level (professional [n=4,876] and recreational [n= 27,373]) and sport category (endurance [n=16,742], team [n=1,002], other [n= 14,457]) without EAMC frequency data. RESULTS: Sweat Na+ concentration differed significantly across cramping categories (H = 293.06, p < 0.001), increasing from 948 mg·L-1 (never) to 1065 mg·L-1 (often). Sweat [Na+] concentration was a predictor of cramping frequency (OR = 1.18 per 250 mg·L-1 increase, 95% CI 1.16–1.20, p < 0.001). Athletes with sweat [Na+] of 1500 mg·L-1 had approximately twice the odds of reporting a higher cramping frequency (never to rarely, rarely to sometimes, sometimes to often, often to always) compared to those at 500 mg·L-1 (OR = 1.94). A significant sex × age interaction was observed (p < 0.001); women in older age groups exhibited higher sweat Na+, with differences most pronounced around menopausal age, while men showed stable values across age groups. CONCLUSION: These data demonstrate an elevated risk of EAMCs with increased sweat sodium concentration. While the modest effect size is consistent with the multifactorial aetiology of EAMC (namely, neuromuscular fatigue and free water loss), these findings suggest that higher individual sweat Na+ losses increase the risk of cramping. Individualising sodium replacement strategies beyond standardised guidelines for endurance athletes warrants further investigation. Additionally, the observed rise in sweat [Na+] in women around menopausal age highlights a need for further research into the potential hormonal and physiological mechanisms driving these differences.
Read CV Lindsey HuntECSS Paris 2023: OP-PN05
INTRODUCTION: Sodium-induced pre-exercise hyperhydration can promote fluid retention, reduce cardiovascular and thermal strain, and improve cycling performance in the heat, yet evidence for its effects on time-trial (TT) running performance remains limited. Prior research has focused on high doses of sodium, yet it is uncertain whether moderate doses have similar physiological and performance outcomes. Furthermore, whilst emerging evidence indicates that glycerol-induced hyperhydration can improve running economy (RE), the impact of sodium-induced hyperhydration on RE remains unclear. METHODS: Ten non-heat-acclimated male runners (age 34 ± 8 years, body mass (BM) 76.9 ± 9.3 kg, V̇O₂ₘₐₓ 56 ± 5 ml·kg⁻¹·min⁻¹) completed three trials in a controlled hot environment (30 °C, 50% humidity, 2.9 m·s⁻¹ airflow). Each trial consisted of 60 min running at 90% of the first lactate threshold, followed by a 5-kilometre TT. Participants ingested 13 mL·kg BM⁻¹ of either water, an 82 mmol·L⁻¹ (ModNa⁺) or a 120 mmol·L⁻¹ (HighNa⁺) sodium chloride (NaCl) solution over a 60 min period, commencing 90 min before and ending 30 min prior to running. Linear mixed models were used to compare between trials, with Sidak-adjusted post hoc tests used to determine differences between trial and/or time where significant main or interaction effects were observed. RESULTS: Fluid retention (+0.205 L, 95% CI: +0.055 to +0.356 L, P = 0.006) and change in plasma volume from baseline (+5.3%, 95% CI: +1.1 to +9.6%, P = 0.004) were higher in HighNa⁺ compared with water, whereas ModNa⁺ did not produce the same effect (P ≥ 0.16). Serum sodium concentration (S[Na⁺]) decreased by 2.06 mmol·L⁻¹ following water ingestion (95% CI: −2.93 to −1.18 mmol·L⁻¹, P < 0.001), but both sodium-containing solutions prevented this serum dilution (P ≥ 0.55). RE during steady-state exercise was improved by ~3.0% in HighNa⁺ compared to water (−5.79 mL·kg⁻¹·km⁻¹, 95% CI: −9.96 to −1.62 mL·kg⁻¹·km⁻¹, P = 0.004), but ModNa⁺ did not elicit the same improvements (P = 0.19). TT performance was not different between trials (Water 19:02 ± 01:48 min, ModNa⁺ 18:44 ± 01:33 min, HighNa⁺ 18:52 ± 01:55 min, P = 0.31). Heart rate, rectal temperature, skin temperature, whole-body sweat rate, local sweat rate and sweat [Na⁺] were also not different between trials (all P > 0.05). CONCLUSION: Pre-exercise ingestion of 13 mL·kg BM⁻¹ of a 120 mmol·L⁻¹ NaCl solution maintained S[Na⁺] and improved hydration status and RE compared with water, whereas ingestion of an 82 mmol·L⁻¹ NaCl solution maintained serum electrolytes but did not enhance hydration status or RE. Neither sodium-containing solution improved 5 km TT performance or attenuated thermal strain compared with water. Overall, although higher drink Na⁺ concentrations more effectively supported fluid retention and reduced the oxygen cost of submaximal running, these physiological benefits did not translate into improved 5-kilometre TT performance.
Read CV Sean SageECSS Paris 2023: OP-PN05