scholarly journals Individual characteristics associated with the magnitude of heat acclimation adaptations

2021 ◽  
Author(s):  
Puck Alkemade ◽  
Nicola Gerrett ◽  
Thijs M. H. Eijsvogels ◽  
Hein A. M. Daanen
Keyword(s):  
Body Mass ◽  
Sweat Rate ◽  
Heat Acclimation ◽  
Individual Characteristics ◽  
Whole Body ◽  
Stress Tests ◽  
Adaptive Responses ◽  
Body Dimensions ◽  
Low Responders ◽  
High Responders

Abstract Purpose The magnitude of heat acclimation (HA) adaptations varies largely among individuals, but it remains unclear what factors influence this variability. This study compared individual characteristics related to fitness status and body dimensions of low-, medium-, and high responders to HA. Methods Twenty-four participants (9 female, 15 male; maximum oxygen uptake [$$\dot{{V}}$$ V ˙ O2peak,kg] 52 ± 9 mL kg−1 min−1) completed 10 daily controlled-hyperthermia HA sessions. Adaptations were evaluated by heat stress tests (HST; 35 min cycling 1.5 W  kg−1; 33 °C, 65% relative humidity) pre- and post-HA. Low-, medium-, and high responder groups were determined based on tertiles (n = 8) of individual adaptations for resting rectal temperature (Tre), exercise-induced Tre rise (ΔTre), whole-body sweat rate (WBSR), and heart rate (HR). Results Body dimensions (p > 0.3) and $$\dot{{V}}$$ V ˙ O2peak,kg (p > 0.052) did not differentiate low-, medium-, and high responders for resting Tre or ΔTre. High WBSR responders had a larger body mass and lower body surface area-to-mass ratio than low responders (83.0 ± 9.3 vs 67.5 ± 7.3 kg; 249 ± 12 vs 274 ± 15 cm2 kg−1, respectively; p < 0.005). Conversely, high HR responders had a smaller body mass than low responders (69.2 ± 6.8 vs 83.4 ± 9.4 kg; p = 0.02). $$\dot{{V}}$$ V ˙ O2peak,kg did not differ among levels of responsiveness for WBSR and HR (p > 0.3). Conclusion Individual body dimensions influenced the magnitude of sudomotor and cardiovascular adaptive responses, but did not differentiate Tre adaptations to HA. The influence of $$\dot{{V}}$$ V ˙ O2peak,kg on the magnitude of adaptations was limited.

Humid heat acclimation does not elicit a preferential sweat redistribution toward the limbs

2004 ◽  
Vol 286 (3) ◽  
pp. R512-R518 ◽  
Author(s):  
Mark J. Patterson ◽  
Jodie M. Stocks ◽  
Nigel A. S. Taylor
Keyword(s):  
Relative Humidity ◽  
Sweat Rate ◽  
Heat Acclimation ◽  
Relative Increase ◽  
Work Rate ◽  
Whole Body ◽  
Stress Tests ◽  
Work Intensity ◽  
Mean Body Temperature ◽  
The Mean

We tested the hypothesis that local sweat rates would not display a systematic postadaptation redistribution toward the limbs after humid heat acclimation. Eleven nonadapted males were acclimated over 3 wk (16 exposures), cycling 90 min/day, 6 days/wk (40°C, 60% relative humidity), using the controlled-hyperthermia acclimation technique, in which work rate was modified to achieve and maintain a target core temperature (38.5°C). Local sudomotor adaptation (forehead, chest, scapula, forearm, thigh) and onset thresholds were studied during constant work intensity heat stress tests (39.8°C, 59.2% relative humidity) conducted on days 1, 8, and 22 of acclimation. The mean body temperature (T̄b) at which sweating commenced (threshold) was reduced on days 8 and 22 ( P < 0.05), and these displacements paralleled the resting thermoneutral T̄b shift, such that the T̄b change to elicit sweating remained constant from days 1 to 22. Whole body sweat rate increased significantly from 0.87 ± 0.06 l/h on day 1 to 1.09 ± 0.08 and 1.16 ± 0.11 l/h on days 8 and 22, respectively. However, not all skin regions exhibited equivalent relative sweat rate elevations from day 1 to day 22. The relative increase in forearm sweat rate (117 ± 31%) exceeded that at the forehead (47 ± 18%; P < 0.05) and thigh (42 ± 16%; P < 0.05), while the chest sweat rate elevation (106 ± 29%) also exceeded the thigh ( P < 0.05). Two unique postacclimation observations arose from this project. First, reduced sweat thresholds appeared to be primarily related to a lower resting T̄b, and more dependent on T̄b change. Second, our data did not support the hypothesis of a generalized and preferential trunk-to-limb sweat redistribution after heat acclimation.

Core Temperature and Sweating in Men and Women During a 15-km Race in Cool Conditions

2020 ◽  
Vol 15 (8) ◽  
pp. 1132-1137
Author(s):  
Coen C.W.G. Bongers ◽  
Dominique S.M. ten Haaf ◽  
Nicholas Ravanelli ◽  
Thijs M.H. Eijsvogels ◽  
Maria T.E. Hopman
Keyword(s):  
Body Mass ◽  
Heat Production ◽  
Sweat Rate ◽  
Core Body Temperature ◽  
Whole Body ◽  
Ambient Conditions ◽  
External Work ◽  
Men And Women ◽  
The Impact ◽  
Cool Conditions

Purpose: Studies often assess the impact of sex on the relation between core body temperature (CBT), whole-body sweat rate (WBSR), and heat production during exercise in laboratory settings, but less is known in free-living conditions. Therefore, the authors compared the relation between CBT, WBSR, and heat production between sexes in a 15-km race under cool conditions. Methods: During 3 editions of the Seven Hills Run (Nijmegen, the Netherlands) with similar ambient conditions (8–12°C, 80–95% relative humidity), CBT and WBSR were measured among 375 participants (52% male) before and immediately after the 15-km race. Heat production was estimated using initial body mass and mean running speed, assuming negligible external work. Results: Men finished the race in 76 (12) minutes and women in 83 (13) minutes (P < .001, effect size [ES] = 0.55). Absolute heat production was higher in men than in women (1185 [163] W vs 867 [122] W, respectively, P < .001, ES = 1.47), even after normalizing to body mass (15.0 [2.2] W/kg vs 13.8 [1.9] W/kg, P < .001, ES = 0.56). Finish CBT did not differ between men and women (39.2°C [0.7°C] vs 39.2°C [0.7°C], P = .71, ES = 0.04). Men demonstrated a greater increase in CBT (1.5°C [0.8°C] vs 1.3°C [0.7°C], respectively, P = .013, ES = 0.31); the sex difference remains after correcting for heat production (P = .004). WBSR was larger in men (18.0 [6.9] g/min) than in women (11.4 [4.7] g/min; P < .001, ES = 0.97). A weak correlation between WBSR and heat production was found irrespective of sex (R2 = .395, P < .001). Conclusions: WBSR was associated with heat production, irrespective of sex, during a self-paced 15-km running race in cool environmental conditions. Men had a higher ΔCBT than women.

scholarly journals Fluid Balance and Sodium Losses During Indoor Tennis Match Play

2011 ◽  
Vol 21 (6) ◽  
pp. 492-500 ◽  
Author(s):  
Matthew J.E. Lott ◽  
Stuart D.R. Galloway
Keyword(s):  
Heart Rate ◽  
Body Mass ◽  
Fluid Balance ◽  
Fluid Intake ◽  
Sweat Rate ◽  
Fluid Replacement ◽  
Whole Body ◽  
Electrolyte Balance ◽  
Match Play ◽  
Tennis Match

This study assessed fluid balance, sodium losses, and effort intensity during indoor tennis match play (17 ± 2 °C, 42% ± 9% relative humidity) over a mean match duration of 68.1 ± 12.8 min in 16 male tennis players. Ad libitum fluid intake was recorded throughout the match. Sweat loss from change in nude body mass; sweat electrolyte content from patches applied to the forearm, calf, and thigh, and back of each player; and electrolyte balance derived from sweat, urine, and daily food-intake analysis were measured. Effort intensity was assessed from on-court heart rate compared with data obtained during a maximal treadmill test. Sweat rate (M ± SD) was 1.1 ± 0.4 L/hr, and fluid-ingestion rate was 1.0 ± 0.6 L/hr (replacing 93% ± 47% of fluid lost), resulting in only a small mean loss in body mass of 0.15% ± 0.74%. Large interindividual variabilities in sweat rate (range 0.3–2.0 L/hr) and fluid intake (range 0.31–2.52 L/hr) were noted. Whole-body sweat sodium concentration was 38 ± 12 mmol/L, and total sodium losses during match play were 1.1 ± 0.4 g (range 0.5–1.8 g). Daily sodium intake was 2.8 ± 1.1 g. Indoor match play largely consisted of low-intensity exercise below ventilatory threshold (mean match heart rate was 138 ± 24 beats/min). This study shows that in moderate indoor temperature conditions players ingest sufficient fluid to replace sweat losses. However, the wide range in data obtained highlights the need for individualized fluid-replacement guidance.

scholarly journals Is active sweating during heat acclimation required for improvements in peripheral sweat gland function?

2009 ◽  
Vol 297 (4) ◽  
pp. R1082-R1085 ◽  
Author(s):  
Michael J. Buono ◽  
Travis R. Numan ◽  
Ryan M. Claros ◽  
Stephanie K. Brodine ◽  
Fred W. Kolkhorst
Keyword(s):  
Sweat Gland ◽  
Sweat Rate ◽  
Heat Acclimation ◽  
Whole Body ◽  
Moderate Intensity ◽  
Sweat Glands ◽  
Exercise Heart Rate ◽  
Sweat Production ◽  
Gland Function ◽  
Pilocarpine Iontophoresis

We investigated whether the eccrine sweat glands must actively produce sweat during heat acclimation if they are to adapt and increase their capacity to sweat. Eight volunteers received intradermal injections of BOTOX, to prevent neural stimulation and sweat production of the sweat glands during heat acclimation, and saline injections as a control in the contralateral forearm. Subjects performed 90 min of moderate-intensity exercise in the heat (35°C, 40% relative humidity) on 10 consecutive days. Heat acclimation decreased end-exercise heart rate (156 ± 22 vs. 138 ± 17 beats/min; P = 0.0001) and rectal temperature (38.2 ± 0.3 vs. 37.9 ± 0.3°C; P = 0.0003) and increased whole body sweat rate (0.70 ± 0.29 vs. 1.06 ± 0.50 l/h; P = 0.030). During heat acclimation, there was no measurable sweating in the BOTOX-treated forearm, but the control forearm sweat rate during exercise increased 40% over the 10 days ( P = 0.040). Peripheral sweat gland function was assessed using pilocarpine iontophoresis before and after heat acclimation. Before heat acclimation, the pilocarpine-induced sweat rate of the control and BOTOX-injected forearms did not differ (0.65 ± 0.20 vs. 0.66 ± 0.22 mg·cm−2·min−1). However, following heat acclimation, the pilocarpine-induced sweat rate in the control arm increased 18% to 0.77 ± 0.21 mg·cm−2·min−1 ( P = 0.021) but decreased 52% to 0.32 ± 0.18 mg·cm−2·min−1 ( P < 0.001) in the BOTOX-treated arm. Using complete chemodenervation of the sweat glands, coupled with direct cholinergic stimulation via pilocarpine iontophoresis, we demonstrated that sweat glands must be active during heat acclimation if they are to adapt and increase their capacity to sweat.

Local versus whole-body sweating adaptations following 14 days of traditional heat acclimation

2016 ◽  
Vol 41 (8) ◽  
pp. 816-824 ◽  
Author(s):  
Martin P. Poirier ◽  
Daniel Gagnon ◽  
Glen P. Kenny
Keyword(s):  
Sweat Gland ◽  
Sweat Rate ◽  
Recovery Period ◽  
Exercise Bout ◽  
Heat Acclimation ◽  
Whole Body ◽  
Regional Variability ◽  
Thermal Chamber ◽  
Local Measurements ◽  
Body Level

The purpose of this study was to examine if local changes in sweat rate following 14 days of heat acclimation reflect those that occur at the whole-body level. Both prior to and following a 14-day traditional heat acclimation protocol, 10 males exercised in the heat (35 °C, ∼20% relative humidity) at increasing rates of heat production equal to 300 (Ex1), 350 (Ex2), and 400 (Ex3) W·m−2. A 10-min recovery period followed Ex1, while a 20-min recovery period separated Ex2 and Ex3. The exercise protocol was performed in a direct calorimeter to measure whole-body sweat rate and, on a separate day, in a thermal chamber to measure local sweat rate (LSR), sweat gland activation (SGA), and sweat gland output (SGO) on the upper back, chest, and mid-anterior forearm. Post-acclimation, whole-body sweat rate was greater during each exercise bout (Ex1: 14.3 ± 0.9; Ex2: 17.3 ± 1.2; Ex3: 19.4 ± 1.3 g·min−1, all p ≤ 0.05) relative to pre-acclimation (Ex1: 13.1 ± 0.6; Ex2: 15.4 ± 0.8; Ex3: 16.5 ± 1.3 g·min−1). In contrast, only LSR on the forearm increased with acclimation, and this increase was only observed during Ex2 (Post: 1.32 ± 0.33 vs. Pre: 1.06 ± 0.22 mg·min−1·cm−2, p = 0.03) and Ex3 (Post: 1.47 ± 0.41 vs. Pre: 1.17 ± 0.23 mg·min−1·cm−2, p = 0.05). The greater forearm LSR post-acclimation was due to an increase in SGO, as no changes in SGA were observed. Overall, these data demonstrate marked regional variability in the effect of heat acclimation on LSR, such that not all local measurements of sweat rate reflect the improvements observed at the whole-body level.

scholarly journals Thermoregulatory adaptations with progressive heat acclimation are predominantly evident in uncompensable, but not compensable, conditions

2019 ◽  
Vol 127 (4) ◽  
pp. 1095-1106 ◽  
Author(s):  
Nicholas Ravanelli ◽  
Geoff Coombs ◽  
Pascal Imbeault ◽  
Ollie Jay
Keyword(s):  
Heat Stress ◽  
Core Temperature ◽  
Heat Dissipation ◽  
Sweat Rate ◽  
Heat Acclimation ◽  
Whole Body ◽  
Evaporative Heat Loss ◽  
Physiological Limits ◽  
Physiological Capacity ◽  
Uncompensable Heat Stress

This study assessed whether, notwithstanding lower resting absolute core temperatures, alterations in time-dependent changes in thermoregulatory responses following partial and complete heat acclimation (HA) are only evident during uncompensable heat stress. Eight untrained individuals underwent 8 wk of aerobic training (i.e., partial HA) followed by 6 days of HA in 38°C/65% relative humidity (RH) (i.e., complete HA). On separate days, esophageal temperature (Tes), arm (LSRarm), and back (LSRback) sweat rate, and whole body sweat rate (WBSR) were measured during a 45-min compensable (37°C/30% RH) and 60-min uncompensable (37°C/60% RH) heat stress trial pre-training (PRE-TRN), post-training (POST-TRN), and post–heat acclimation (POST-HA). For compensable heat stress trials, resting Tes was lower POST-TRN (36.74 ± 0.27°C, P = 0.05) and POST-HA (36.60 ± 0.27°C, P = 0.001) compared with PRE-TRN (36.99 ± 0.19°C); however, ΔTes was similar in all trials (PRE-TRN:0.40 ± 0.23°C; POST-TRN:0.42 ± 0.20°C; POST-HA:0.43 ± 0.12°C, P = 0.97). While LSRback was unaltered by HA ( P = 0.94), end-exercise LSRarm was higher POST-TRN (0.70 ± 0.14 mg·cm−2·min−1, P < 0.001) and POST-HA (0.75 ± 0.16 mg·cm−2·min−1, P < 0.001) compared with PRE-TRN (0.61 ± 0.15 mg·cm−2·min−1). Despite matched evaporative heat balance requirements, steady-state WBSR (31st–45th min) was greater POST-TRN (12.7 ± 1.0 g/min, P = 0.02) and POST-HA (12.9 ± 0.8 g/min, P = 0.004), compared with PRE-TRN (11.7 ± 0.9 g/min). For uncompensable heat stress trials, resting Tes was lower POST-TRN (36.77 ± 0.22°C, P = 0.05) and POST-HA (36.62 ± 0.15°C, P = 0.03) compared with PRE-TRN (36.86 ± 0.24°C). But ΔTes was smaller POST-TRN (0.77 ± 0.19°C, P = 0.05) and POST-HA (0.75 ± 0.15°C, P = 0.04) compared with PRE-TRN (1.10 ± 0.32°C). LSRback and LSRarm increased with HA ( P < 0.007), supporting the greater WBSR with HA (POST-TRN:14.4 ± 2.4 g/min, P < 0.001; POST-HA:16.8 ± 2.8 g/min, P < 0.001) compared with PRE-TRN (12.7 ± 3.2 g/min). In conclusion, the thermal benefits of HA are primarily evident when conditions challenge the physiological capacity to dissipate heat. NEW & NOTEWORTHY We demonstrate that neither partial nor complete heat acclimation alters the change in core temperature during compensable heat stress compared with an unacclimated state, despite a marginally greater whole body sweat rate. However, the greater local and whole body sweat rate with partial and complete heat acclimation reduced the rise in core temperature during 60 min of uncompensable heat stress compared with an unacclimated state, suggesting the improvements in heat dissipation associated with heat acclimation are best observed when the upper physiological limits for evaporative heat loss are challenged.

scholarly journals A comparison of thermoregulatory responses to exercise between mass-matched groups with large differences in body fat

2016 ◽  
Vol 120 (6) ◽  
pp. 615-623 ◽  
Author(s):  
Sheila Dervis ◽  
Geoff B. Coombs ◽  
Georgia K. Chaseling ◽  
Davide Filingeri ◽  
Jovana Smoljanic ◽  
...  
Keyword(s):  
Lean Body Mass ◽  
Body Mass ◽  
Body Fat ◽  
Sweat Rate ◽  
Whole Body ◽  
Total Body Mass ◽  
Percentage Body Fat ◽  
Thermoregulatory Responses ◽  
Local Sweat Rate ◽  
Total Body

We sought to determine 1) the influence of adiposity on thermoregulatory responses independently of the confounding biophysical factors of body mass and metabolic heat production (Hprod); and 2) whether differences in adiposity should be accounted for by prescribing an exercise intensity eliciting a fixed Hprod per kilogram of lean body mass (LBM). Nine low (LO-BF) and nine high (HI-BF) body fat males matched in pairs for total body mass (TBM; LO-BF: 88.7 ± 8.4 kg, HI-BF: 90.1 ± 7.9 kg; P = 0.72), but with distinctly different percentage body fat (%BF; LO-BF: 10.8 ± 3.6%; HI-BF: 32.0 ± 5.6%; P < 0.001), cycled for 60 min at 28.1 ± 0.2°C, 26 ± 8% relative humidity (RH), at a target Hprod of 1) 550 W (FHP trial) and 2) 7.5 W/kg LBM (LBM trial). Changes in rectal temperature (ΔTre) and local sweat rate (LSR) were measured continuously while whole body sweat loss (WBSL) and net heat loss (Hloss) were estimated over 60 min. In the FHP trial, ΔTre (LO-BF: 0.66 ± 0.21°C, HI-BF: 0.87 ± 0.18°C; P = 0.02) was greater in HI-BF, whereas mean LSR (LO-BF 0.52 ± 0.19, HI-BF 0.43 ± 0.15 mg·cm−2·min−1; P = 0.19), WBSL (LO-BF 586 ± 82 ml, HI-BF 559 ± 75 ml; P = 0.47) and Hloss (LO-BF 1,867 ± 208 kJ, HI-BF 1,826 ± 224 kJ; P = 0.69) were all similar. In the LBM trial, ΔTre (LO-BF 0.82 ± 0.18°C, HI-BF 0.54 ± 0.19°C; P < 0.001), mean LSR (LO-BF 0.59 ± 0.20, HI-BF 0.38 ± 0.12 mg·cm−2·min−1; P = 0.04), WBSL (LO-BF 580 ± 106 ml, HI-BF 381 ± 68 ml; P < 0.001), and Hloss (LO-BF 1,884 ± 277 kJ, HI-BF 1,341 ± 184 kJ; P < 0.001) were all greater at end-exercise in LO-BF. In conclusion, high %BF individuals demonstrate a greater ΔTre independently of differences in mass and Hprod, possibly due to a lower mean specific heat capacity or impaired sudomotor control. However, thermoregulatory responses of groups with different adiposity levels should not be compared using a fixed Hprod in watts per kilogram lean body mass.

Changes in Hydration Factors Over the Course of Heat Acclimation in Endurance Athletes

2021 ◽  
pp. 1-6
Author(s):  
Yasuki Sekiguchi ◽  
Courteney L. Benjamin ◽  
Samantha O. Dion ◽  
Ciara N. Manning ◽  
Jeb F. Struder ◽  
...  
Keyword(s):  
Oxygen Consumption ◽  
Relative Humidity ◽  
Body Mass ◽  
Fluid Intake ◽  
Sweat Rate ◽  
Maximal Oxygen Consumption ◽  
Heat Acclimation ◽  
Endurance Athletes ◽  
Body Mass Loss ◽  
Ad Libitum

The purpose of this study was to examine the effect of heat acclimation (HA) on thirst levels, sweat rate, and percentage of body mass loss (%BML), and changes in fluid intake factors throughout HA induction. Twenty-eight male endurance athletes (mean ± SD; age, 35 ± 12 years; body mass, 73.0 ± 8.9 kg; maximal oxygen consumption, 57.4 ± 6.8 ml·kg−1·min−1) completed 60 min of exercise in a euhydrated state at 58.9 ± 2.3% velocity of maximal oxygen consumption in the heat (ambient temperature, 35.0 ± 1.3 °C; relative humidity, 48.0 ± 1.3%) prior to and following HA where thirst levels, sweat rate, and %BML were measured. Then, participants performed 5 days of HA while held at hyperthermia (38.50–39.75 °C) for 60 min with fluid provided ad libitum. Sweat volume, %BML, thirst levels, and fluid intake were measured for each session. Thirst levels were significantly lower following HA (pre, 4 ± 1; post, 3 ± 1, p < .001). Sweat rate (pre, 1.76 ± 0.42 L/hr; post, 2.00 ± 0.60 L/hr, p = .039) and %BML (pre, 2.66 ± 0.53%; post, 2.98 ± 0.83%, p = .049) were significantly greater following HA. During HA, thirst levels decreased (Day 1, 4 ± 1; Day 2, 3 ± 2; Day 3, 3 ± 2; Day 4, 3 ± 1; Day 5, 3 ± 1; p < .001). However, sweat volume (Day 1, 2.34 ± 0.67 L; Day 2, 2.49 ± 0.58 L; Day 3, 2.67 ± 0.63 L; Day 4, 2.74 ± 0.61 L; Day 5, 2.74 ± 0.91 L; p = .010) and fluid intake (Day 1, 1.20 ± 0.45 L; Day 2, 1.52 ± 0.58 L; Day 3, 1.69 ± 0.63 L; Day 4, 1.65 ± 0.58 L; Day 5, 1.74 ± 0.51 L; p < .001) increased. In conclusion, thirst levels were lower following HA even though sweat rate and %BML were higher. Thirst levels decreased while sweat volume and fluid intake increased during HA induction. Thus, HA should be one of the factors to consider when planning hydration strategies.

Effect of plasma prolactin on sweat rate and sweat composition during exercise in men

1993 ◽  
Vol 264 (5) ◽  
pp. F816-F820
Author(s):  
P. Boisvert ◽  
G. R. Brisson ◽  
F. Peronnet
Keyword(s):  
Sweat Rate ◽  
Cycle Ergometer ◽  
Plasma Prolactin ◽  
Young Males ◽  
Low Responders ◽  
Exercise Induced ◽  
Plasma Prl ◽  
Response To Exercise ◽  
High Responders

We investigated the role of the exercise-induced elevation of plasma prolactin (PRL) concentration on sweat rate and composition during prolonged exercise in men. Two groups of healthy young males (20-26 yr old) showing a high (high responders; n = 8) or a low (low responders; n = 7) response of plasma PRL concentration to exercise were studied during a 60-min period of exercise on a cycle ergometer (65% maximum O2 consumption) in warm conditions (26.2 +/- 0.1 degrees C; 57 +/- 1% relative humidity), 1 h after receiving 1.25 mg bromocriptine (BRC) per os or a placebo. In high responders, administration of BRC totally abolished the threefold increase in plasma PRL observed in response to exercise with placebo [placebo, 10 +/- 2 (rest) and 30 +/- 2 micrograms/l (exercise); BRC, 9 +/- 1 (rest) and 8 +/- 1 microgram/l (exercise)]. The latter was associated with a significant decrease in sweat rate (2.7 +/- 0.5 to 1.9 +/- 0.3 microliter.cm-2.min-1) and a significant increase in sweat Na+ concentration (57 +/- 7 to 68 +/- 5 mmol/l). BRC also reduced the small response in plasma PRL concentration observed in low responders [placebo, 10 +/- 1 (rest) and 15 +/- 1 microgram/l (exercise); BRC, 9 +/- 1 (rest) and 7 +/- 1 microgram/l (exercise)], but this was not associated with any change in sweat rate (2.2 +/- 0.2 to 1.9 +/- 0.3 microliter.cm-2.min-1) or in sweat Na+ concentration (63 +/- 10 to 64 +/- 9 mmol/l).(ABSTRACT TRUNCATED AT 250 WORDS)

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