Antoine Jolicoeur Desroches

Pre-exercise internal cooling through cold-water-induced hyperhydration may attenuate increases in core body temperature (T_C) and improve endurance performance. Quantifying the extent of reduction in T_C induced by hyperhydration is important for optimizing its timing before exercise. We compared T_C values obtained from a wearable sensor, the CORE, with those of a gastrointestinal temperature telemetric sensor (G_TS) during hyperhydration. Eleven participants (two women; age: 24 ± 4 yrs) completed a 120 min seated period where they consumed, over the first 60 min, four boluses of 4 °C water (7.5 mL · kg fat-free mass [FFM]⁻¹), each containing 0.35 g · kg FFM⁻¹ of glycerol. Measures of T_C were taken every 20 min with both sensors. According to the G_TS, hyperhydration induced a peak T_C decline of −0.76 ± 0.31 °C at min 60; at this time, the change in T_C from baseline estimated by the CORE was −0.09 °C ± 0.20 °C. The greatest decline in T_C detected by the CORE was −0.11 ± 0.19 °C. Bland and Altman analyses revealed that average T_C declines of –0.1, −0.2, −0.3, −0.4, −0.5 and −0.6 °C from baseline were associated with T_C values estimated by the CORE that were respectively +0.29, +0.41, +0.57, +0.65, +0.77 and +0.89 °C higher than the G_TS. An intraclass correlation coefficient of 0.12 suggested poor agreement between instruments. These results raise concerns about the ability of the CORE to detect changes in T_C induced by a hyperhydration protocol generating a substantial heat sink.

Pre-exercise internal cooling through cold water-induced hyperhydration may attenuate increases in core body temperature (T_C) and improve endurance performance. Quantifying the extent of reduction in T_C induced by hyperhydration is important for optimizing its timing before exercise. We compared T_C values obtained from a wearable sensor, the CORE, with those of a gastrointestinal temperature telemetric sensor (G_TS) during hyperhydration. Eleven participants (2 women; age: 24 ± 4 yrs) completed a 120 min seated period where they consumed, over the first 60 min, four boluses of 4 °C water (7.5 mL · kg fat-free mass [FFM]⁻¹), each containing 0.35 g · kg FFM⁻¹ of glycerol. Measures of T_C were taken every 20 min with both sensors. According to the G_TS, hyperhydration induced a peak T_C decline of − 0.76 ± 0.31 °C at min 60; at this time, the change in T_C from baseline estimated by the CORE was − 0.09 °C ± 0.20 °C. The greatest decline in T_C detected by the CORE was − 0.11 ± 0.19 °C. Bland and Altman analyses revealed that average T_C declines of − 0.2, − 0.3, − 0.4, − 0.5 and − 0.6 °C from baseline were associated with T_C values estimated by the CORE that were respectively + 0.41, + 0.57, + 0.65, + 0.77 and + 0.89 °C higher than the G_TS. An intraclass correlation coefficient of 0.12 suggested poor agreement between instruments. These results raise concerns about the ability of the CORE to detect changes in T_C induced by a hyperhydration protocol generating a substantial heat sink.

Background: Leading sports medicine and nutrition organizations recommend replacing sodium losses during prolonged exercise; however, practical guidance for implementing sodium replacement strategies remains limited. Estimating sodium needs during exercise requires assessment of both whole-body sweat sodium concentration (WBSSC) and sweat rate. Objectives: This study focused on WBSSC by examining its temporal stability, reproducibility, and predictability during prolonged cycling exercise while drinking according to two hydration strategies. Methods: Using a randomized, crossover, counterbalanced design, eight highly trained men completed two 5 h cycling sessions (183 ± 14 W, 30 °C) while consuming fluids either in a programmed (P) or ad libitum (A_L) fashion. Sweat was collected with patches applied on the forearm for ~20 min before sampling, which occurred at ~40, 130, 220, and 290 min. Local sweat sodium concentration was converted to WBSSC using a validated equation. Results: A main effect of time was observed for WBSSC (p < 0.05), with only the 40 min time point differing from later measurements; no condition or interaction effects were detected. The within-trial typical variation in WBSSC was 7.2 mmol·L⁻¹ for P and 6.1 mmol·L⁻¹ for A_L, while the between-trial typical variation was 5.6 mmol·L⁻¹. The WBSSC measured at 40 min predicted mean exercise WBSSC with good precision and moderate stability (y = 0.2738 + 1.3397x, R² = 0.87, standard error of the estimate = 5.4 mmol·L⁻¹, 95% confidence interval slope = 0.82–1.86 mmol·L⁻¹). Conclusions: These findings indicate that during prolonged cycling exercise, WBSSC (1) varies trivially within and between trials; (2) can reasonably be predicted using a single sweat sample and; (3) is not influenced by P or A_L drinking.

This study reveals, for the first time, that mild hypohydration equivalent to ∼1% of body mass does not alter pain perception in healthy older adults when they are blinded to their hydration status, despite electroencephalography signals showing modulation of pain-related brain responses.

Exercise performed under hot/humid conditions can hinder endurance performance. The Omius^TM headband (OH) is purported to reduce the perception of heat and improve performance. We examined the impact of OH on selected thermal and cardiovascular functions, subjective perceptions and running performance. Using a randomized crossover protocol, 10 trained male athletes (28 ± 4 yrs) completed two trials (OH and SH (sham headband), 35.0 ± 0.3ºC, 56 ± 3% relative humidity) comprising 70 min of running (60% O_2max) followed by a 5-km running time-trial (TT). Heart rate, perceived exertion and whole-body thermal comfort did not significantly differ between OH and SH during the submaximal running effort and the TT. Rectal temperature was significantly lower with SH (− 0.18 ± 0.17ºC) than OH prior to the submaximal running effort; this significant difference persisted during the submaximal running effort. Rectal temperature did not differ significantly between conditions during the TT. Forehead temperature was significantly lower with OH than SH during the submaximal running effort, but no significant difference was observed at the end of the TT. Perceived forehead thermal comfort was only significantly lower with OH than SH during the submaximal running effort. TT time did not significantly differ between OH (19.8 ± 1.2 min) and SH (20.2 ± 1.0 min). We conclude that in hot/humid conditions, OH does not improve heart rate, forehead and rectal temperatures, perceived exertion, whole-body and forehead thermal comfort and performance during a 5-km running TT preceded by 70 min of moderate-intensity running.

A drinking strategy aiming to replace a given percentage of the sweat losses incurred during exercise should result in reproducible fluid intake volume and, hence, fluid balance from one exercise session to the other performed under similar scenarios. Whether this may also be the case with ad libitum drinking during exercise is unclear. We characterized the repeatability of ad libitum fluid intake during repeated 1 h exercise sessions and examine its effect over time on fluid balance and selected physiological functions and perceptual sensations. Twelve (3 women) healthy individuals participated in this study. At weekly intervals, they completed 4, 2 x 30 min walking/jogging exercise bouts (55% VO2max, 40°C, 20-30% relative humidity) interspersed by a 3 min recovery period. During exercise, participants replaced water (20°C) ad libitum. There were no significant differences among the 4 exercise sessions for absolute fluid intake volume (~ 1000 mL · h-1), percent body mass loss (~ 0.4%), sweat rate (~ 1300 mL · h-1) and percent of sweat loss replaced by fluid intake (~ 80%). Heart rate, rectal temperature and perceived thirst and heat stress did not differ significantly between the first and fourth exercise session. Perceived exertion was significantly lower during the fourth vs. the first exercise session, but the difference was trivial, < 1 arbitrary unit. In conclusion, ad libitum fluid intake during 4 successive identical 1 h walking/jogging sessions conducted in the heat will result in similar fluid intake volumes and perturbations in fluid balance, heart rate, rectal temperature and perceived thirst, heat stress and exertion.