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Objectives: Determine whether five days of heat acclimation reduces cardiovascular and thermoregulatory strain during consecutive exercise-heat exposures on the sixth day in the heat., Design: Pair-matched randomized control trial., Methods: Twenty-four males completed two, 120min exercise sessions (Session 1, Session 2) in a single day before (Day 1) and after (Day 6) four additional days of exercise in either hot (HOT: 40°C, 40% relative humidity, n=16) or temperate (CON: 23°C, 25% relative humidity, n=8) environments. A mixed-methods heat acclimation approach was implemented. Day 2 consisted of 120min of moderate-high intensity treadmill exercise. Days 3-5 consisted of 90min of moderate-high intensity exercise, with HOT completing this in a hyperthermia clamped manner at rectal temperature ≥38.5°C, and CON<38.5°C., Results: Session 1 end of exercise rectal temperature and heart rate were lower on Day 6 compared to Day 1 for HOT (p=0.012, p=0.003) but not CON (p=0.152, p=0.437). Session 2 end of exercise rectal temperature was not different between days for HOT (p=0.104) or CON (p=0.275). Session 2 end of exercise heart rate was lower on Day 6 compared to Day 1 for HOT (p=0.004) and CON (p=0.039). Session 1 sweat sensitivity was greater on Day 6 compared to Day 1 for HOT (p=0.039) but not CON (p=0.257). Sweat rate was unchanged for HOT and CON between days during Session 1 (p=0.184, p=0.962) and Session 2 (p=0.051, p=0.793), respectively., Conclusions: Five days of heat acclimation reduced cardiovascular strain but not thermoregulatory strain during the second, consecutive exercise-heat exposure. CLINICALTRIALS., Gov Identifier: NCT04053465., (Copyright © 2021 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.)

The combination of hyperthermia, dehydration, and strenuous exercise can result in severe reductions in kidney function, potentially leading to acute kidney injury (AKI). We sought to determine whether six days of heat acclimation (HA) mitigates the rise in clinical biomarkers of AKI during strenuous exercise in the heat. Twenty men completed two consecutive 2 h bouts of high-intensity exercise in either hot ( n = 12, 40 °C, 40% relative humidity) or mild ( n = 8, 24 °C, 21% relative humidity) environments before (PreHA) and after (PostHA) 4 days of 90-120 min of exercise per day in a hot or mild environment. Increased clinical biomarkers of AKI (CLINICAL) was defined as a serum creatinine increase ≥0.3 mg·dL -1 or estimated glomerular filtration rate (eGFR) reduction >25%. Creatinine similarly increased in the hot environment PreHA (0.35 ± 0.23 mg·dL -1 ) and PostHA (0.39 ± 0.20 mg·dL -1 ), with greater increases than the mild environment at both time points (0.11 ± 0.07 mg·dL -1 , 0.08 ± 0.06 mg·dL -1 , p ≤ 0.001), respectively. CLINICAL occurred in the hot environment PreHA ( n = 9, 75%), with fewer participants with CLINICAL PostHA ( n = 7, 58%, p = 0.007), and no participants in the mild environment with CLINICAL at either time point. Percent change in plasma volume was predictive of changes in serum creatinine PostHA and percent changes in eGFR both PreHA and PostHA. HA did not mitigate reductions in eGFR nor increases in serum creatinine during high-intensity exercise in the heat, although the number of participants with CLINICAL was reduced PostHA.

Objectives: An exercise session in a hot environment may increase thermal strain during subsequent exercise sessions on the same and consecutive days. Therefore, this study was conducted to determine lasting physiological strain from moderate-high intensity, intermittent exercise in heat on subsequent exercise., Design: Repeated measures laboratory study., Methods: Seventeen healthy, recreationally active men (age: 22±3 y, maximal oxygen consumption: 54.6±5.3mLkg -1 min -1 ) underwent two intermittent moderate-high intensity aerobic exercise sessions separated by 2h of rest one day, followed by one session 24h later in a 40°C, 40% relative humidity environment. Heart rate, rectal temperature, heat stress perception, and environmental symptoms were assessed., Results: 100%, 35%, and 71% of participants completed the full exercise protocol during the first exercise session, second exercise session, and the following day, respectively. Exercising heart rate and rectal temperature were greater during the second exercise session (189±11bpm, 38.80±0.47°C) than the first identical exercise session (180±17bpm, p=0.004; 38.41±0.52°C, p=0.001), respectively. Immediate post-exercise heart rate, rectal temperature, thirst, thermal sensation, fatigue, and perceived exertion were similar among exercise sessions despite a shorter exercise duration during the second exercise session (93±27min, p=0.001) and the following day (113±12min, p=0.032) than the first exercise session (120±0min)., Conclusions: Moderate-high-intensity intermittent exercise in the heat resulted in greater heat strain during a second exercise session the same day, and exercise the subsequent day., (Copyright © 2019 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.)

Adams, EL, Casa, DJ, Huggins, RA, DeMartini-Nolan, JK, Stearns, RL, Kennedy, RM, Bosworth, MM, DiStefano, LJ, Armstrong, LE, and Maresh, CM. Heat exposure and hypohydration exacerbate physiological strain during load carrying. J Strength Cond Res 33(3): 727-735, 2019-Heat exposure and hypohydration induce physiological and psychological strain during exercise; however, it is unknown if the separate effects of heat exposure and hypohydration are synergistic when co-occurring during loaded exercise. This study compared separate and combined effects of heat exposure and hypohydration on physiological strain, mood state, and visual vigilance during loaded exercise. Twelve men (mean ± SD; age, 20 ± 2 years; body mass, 74.0 ± 8.2 kg; maximal oxygen uptake, 57.0 ± 6.0 ml·kg·min) completed 4 trials under the following conditions: euhydrated temperate (EUT), hypohydrated temperate (HYT), euhydrated hot (EUH), and hypohydrated hot (HYH). Exercise was 90 minutes of treadmill walking (∼50% V[Combining Dot Above]O2max, 5% grade) while carrying a 45-lb rucksack. Profile of Mood States and the Scanning Visual Vigilance Test were completed before and after exercise. The separate effects of heat exposure (EUH) and hypohydration (HYT) on post-exercise rectal temperature (Tre) were similar (38.25 ± 0.63°C vs. 38.22 ± 0.29°C, respectively, p > 0.05), whereas in combination (HYH), post-exercise Tre was far greater (39.32 ± 0.43°C). Increase in Tre per 1% body mass loss (BML) for HYH (vs. EUH) was greater than HYT (vs. EUT) (0.32 vs. 0.04°C, respectively, p = 0.02); heart rate increase per 1% BML for HYH (vs. EUH) was 7 b·min compared with HYT (vs. EUT) at 3 b·min (p = 0.30). Hypohydrated hot induced greater mood disturbance (post-exercise - pre-exercise) (35 ± 21 units) compared with other conditions (EUT = 3 ± 9 units; HYT = 3 ± 16 units; EUH = 16 ± 26 units; p < 0.001). No differences occurred in visual vigilance (p > 0.05). Independently, heat exposure and hypohydration induced similar physiological strain during loaded exercise; when combined, heat exposure with hypohydration, synergistically exacerbated physiological strain and mood disturbance.

Objectives: To determine if intermittent exercise-heat exposures (IHE) every fifth day sustain heat acclimation (HA) adaptations 25 days after initial HA., Design: Randomized control trial., Methods: Sixteen non-heat acclimatized men heat acclimated during 10-11 days of exercise in the heat (40°C, 40% RH). A heat stress test (120min, 45% V˙O 2peak ) before (Pre HA) and after HA (Post HA) in similar hot conditions assessed HA status. Pair-matched participants were randomized into a control group (CON; n=7) that exercised in a temperate environment (24°C, 21%RH) or IHE group (n=9) that exercised in a hot environment (40°C, 40%RH) every fifth day for 25 days following HA (+25d) with out-of-laboratory exercise intensity and duration recorded. Both groups completed +25d in the hot condition., Results: Both groups heat acclimated similarly (p>0.05) evidenced by lower heart rate (HR), thermoregulatory, physiological, and perceptual responses (perceived exertion, fatigue, thermal sensation) Pre HA vs. Post HA (p≤0.05). At +25d, post-exercise HR (p=0.01) and physiological strain index (p<0.05) but neither T re (p=0.18) nor sweat rate (p=0.44) were lower in IHE vs. CON. In IHE only, post-exercise T re and perceptual responses at Post HA and +25d were lower than Pre HA (p≤0.01). +25d post-exercise epinephrine was higher in CON vs. IHE (p=0.04). Exercise intensity during out-of-lab exercise and +25d post-exercise HR were correlated (r=-0.89, p=0.02) in IHE., Conclusions: Exercise-heat exposures every fifth day for 25 days and regular intense physical activity after HA sustained HR and T re adaptations and reduced perceptual and physiological strain during exercise-heat stress ∼1 month later., (Copyright © 2018 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.)

Stress-inducible Hsp72 is a potential biomarker to track risk of exertional heat illness during exercise/environmental stress. Characterization of extracellular (eHsp72) vs cellular Hsp72 (iHsp72) responses is required to define the appropriate use of Hsp72 as a reliable biomarker. In each of four repeat visits, participants (n = 6 men, 4 trials; total n = 24): (a) passively dehydrated overnight, (b) exercised (2 h) with no fluid in a hot, humid environmental chamber, (c) rested and rehydrated (1 h), (d) maximally exercised for 0.5 h, and (e) returned after 24 h of at-home recovery and rehydration. We measured rectal temperature, hydration status (% body mass loss, urine markers, serum osmolality), and Hsp72 (ELISA, flow cytometry. eHsp72 (circulating) and iHsp72 (CD3 + PBMCs) correlated (P < 0.05) with markers of heat, exercise, and dehydration stresses. eHsp72 immediately post-exercise (>15% above baseline, P < 0.05) decreased back to baseline levels by 1 h post-exercise, but iHsp72 expression continued to rise and remained elevated 24 h post-exercise (~2.5-fold baseline, P < 0.05). These data suggest that in addition to the classic physiological biomarkers of exercise heat stress, using cellular Hsp72 as an indicator of lasting effects of stress into recovery may be most appropriate for determining long-term effects of stress on risk for exertional heat illness., (© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

This study investigated the effects of environmental temperature on repetitive box lifting (RBL) performance, associated stress hormone and creatine kinase (CK) responses. Ten healthy males performed two experimental trials in a random crossover design. The trials consisted of three 40 min (10 min sitting, 20 min standing, and 10 min RBL) circuits performed in either 23 °C or 38 °C followed by a 180 min seated recovery period in 23 °C. RBL performance (i.e., number of boxes lifted) was reduced (p ≤ 0.05) in 38 °C compared to the 23 °C trial. Physiological Strain Index was significantly different between trials (38 °C: 8.5 ± 1.1 versus 23 °C: 7.2 ± 0.7; p ≤ 0.01). Plasma testosterone was elevated (p ≤ 0.05) across both trials and then decreased at 60 min recovery, compared to pre-exercise (PRE) measures, but was higher (p ≤ 0.05) during the 38 °C trial. Plasma cortisol increased (p ≤ 0.05) at 60 min during both trials and remained elevated until 120 min in 23 °C, and until 60 min recovery in 38 °C. Serum CK was greater through 48 hr post compared to PRE values in both trials. Thus, 10 min RBL performance was reduced in 38 °C despite the 30-min rest periods between RBL intervals. Plasma testosterone and cortisol were generally higher during the 38 °C trial, suggesting a greater stress response. Additional research is needed to determine optimal work:rest cycles for maximizing work performance in thermally oppressive environments.

Background: The purpose was to: 1) correlate and compare the long Environmental Symptoms Questionnaire (56-ESQ) with markers of heat acclimation; 2) compare the 56-ESQ with a modified version of the ESQ (14-ESQ) over a 10-d exercise heat acclimation protocol; 3) correlate both scales with physiological data; and 4) determine those questions most sensitive to heat acclimation responses to further refine the 14-ESQ. This is reported as a 12-question ESQ (12-ESQ), which was correlated with physiological data., Methods: There were 10 non-trained, non-heat-acclimatized men (age 20 +/- 1 yr; height 184 +/- 8 cm; weight 81.7 +/- 12.2 kg; percent body fat 10.1 +/- 2.9%) who undertook 10 consecutive days of heat acclimation (walking at 5.6 km x h(-1), 5% grade, 90 min duration; 33 degrees C, 30-50% relative humidity). ESQ forms were completed on days 1, 4, 7, and 10 pre- and post-exercise. During exercise, rectal temperature (T(r)), heart rate (HR), and rating of perceived exertion (RPE) were recorded., Results: Verification of heat acclimation was based on T(r) and HR, which were significantly lower on day 4 (38.11 +/- 0.25 degrees C, 143 +/- 13 bpm) vs. day 1 (38.46 +/- 0.47 degrees C, 158 +/- 17 bpm) and all subsequent days. All ESQ scales demonstrated a significant effect of time, supporting evidence of heat acclimation. The 56-, 14-, and 12-ESQ post-exercise scores were significantly correlated with HR (r2 = 0.424, 0.353, and 0.430, respectively). The 12-ESQ was correlated with T(r) (r2 = 0.400)., Discussion: The 12- and 14-ESQ tracked well with the 56-ESQ. All ESQs were able to track physiological variables and symptoms of heat stress. All ESQ forms may be used as an efficient method to indicate environmental heat stress and symptoms.

Purpose: This study aimed to evaluate the effects of hypohydration and hyperthermia during exercise on movement technique and postural control., Methods: Twelve healthy men (age = 20 ± 2 yr, height = 182 ± 8 cm, mass = 74.0 ± 8.2 kg, V˙O2max = 57.0 ± 6.0 mL·kg·min; mean ± SD) completed four randomized test sessions: euhydrated temperate (EUT), euhydrated hot (EUH), hypohydrated temperate (HYT), and hypohydrated hot (HYH). Temperate and hot conditions were performed in 18.0°C ± 0.2°C, 50.0% ± 3.5% relative humidity, and 34.0°C ± 0.3°C, 45.0% ± 4.5% relative humidity, respectively. Movement technique and postural control were assessed before exercise (PRE), after exercise (POST), and after recovery (REC). Movement technique was evaluated using the Landing Error Scoring System (LESS). Postural control was assessed using the Balance Error Scoring System (BESS) and center-of-pressure sway velocity (SV) and elliptical sway area (ESA) during a dynamic balance test. The 90-min treadmill exercise protocol (1.34-1.78 m·s; 5% grade) required subjects to walk carrying a 20.5-kg rucksack. Subjects sat quietly in the test environment during a 60-min recovery period after exercise. Repeated-measures ANOVAs with a Tukey-HSD post hoc test evaluated differences between time and condition for dependent variables., Results: Exercise during HYH significantly increased LESS scores (PRE = 3.72 ± 1.73, POST = 4.42 ± 1.75) compared with HYT (3.75 ± 1.76) and EUH (3.61 ± 1.71) (P < 0.05). LESS scores remained elevated during REC for HYH compared with EUT (4.39 ± 1.47 vs 3.47 ± 2.05, P < 0.05). The HYH condition caused the greatest number of BESS errors (P = 0.02), largest ESA (P < 0.05), and highest SV (P = 0.02). Regardless of the condition, participants had the most BESS errors (P = 0.002) and highest SV (P = 0.003) during POST compared with the PRE and REC., Conclusions: Hypohydration during exercise in the heat impairs neuromuscular control. These findings suggest that physical activity in the heat while dehydrated may affect parameters associated with a higher risk of injury.

Introduction: Orthostatic hypotension (OH) occurs among several populations; elevated temperatures increase an individual's susceptibility, whereas the effect of sleep loss (SL) remains inconclusive. The purpose was: 1) to evaluate the effects of 10 d of heat acclimation (HA) and 28 h of SL on OH; and 2) to determine the best measurements to assess OH in clinical and field settings., Methods: There were 11 men (mean +/- SD; age, 20 +/- 1 yr; mass, 81.7 +/- 12.2 kg) who underwent a repeated measures research design. Before and after 90 min of HA, with the 11th day performed in conjunction with SL, subjects performed a lie-to-stand test where blood pressure (BP), heart rate (HR), and OH signs and symptoms were obtained., Results: OH incidence and intensity, assessed via acute changes in post-exercise systolic BP (SBP), significantly decreased during HA from Day 2 (15 +/- 12 mmHg) to Day 8 (8 +/- 8 mmHg), while SL showed no effect. As OH responses decreased, concomitant HR increases diminished from Day 2 (113 +/- 15 bpm) to Day 8 (103 +/- 14 bpm). Post-exercise lightheadedness, dizziness, and nausea significantly decreased from Day 2 to Day 8, while no changes were associated with SL., Conclusions: During HA, BP control improved and cardiovascular strain was reduced, along with OH signs and symptoms; mild SL had no measurable effect. Acute HR changes may be explained by decreased cardiac output and increased stroke volume. In clinical settings, SBP delta may indicate the threshold at which OH signs and symptoms arise. In the absence of a sphygmomanometer, HR taken upon standing, or ratings of lightheadedness and dizziness may be used as alternative field expedient techniques.

The purpose of this study was to assess whether a lymphocyte heat shock response and altered heat tolerance to ex vivo heat shock is evident during acclimation. We aimed to use flow cytometry to assess the CD3(+)CD4(+) T lymphocyte cell subset. We further aimed to induce acclimation using moderately stressful daily exercise-heat exposures to achieve acclimation. Eleven healthy males underwent 11 days of heat acclimation. Subjects walked for 90 min (50 ± 8% VO(2max)) on a treadmill (3.5 mph, 5% grade), in an environmental chamber (33°C, 30-50% relative humidity). Rectal temperature (°C), heart rate (in beats per minute), rating of perceived exertion , thermal ratings, hydration state, and sweat rate were measured during exercise and recovery. On days 1, 4, 7, 10, and 11, peripheral blood mononuclear cells were isolated from pre- and post-exercise blood samples. Intracellular and surface HSP70 (SPA-820PE, Stressgen, Assay Designs), and annexin V (ab14085, Abcam Inc.), as a marker of early apoptosis, were measured on CD3(+) and CD4(+) (sc-70624, sc-70670, Santa Cruz Biotechnology) gated lymphocytes. On day 10, subjects experienced 28 h of sleep loss. Heat acclimation was verified with decreased post-exercise rectal temperature, heart rate, and increased sweat rate on day 11, versus day 1. Heat acclimation was achieved in the absence of significant changes in intracellular HSP70 mean fluorescence intensity and percent of HSP70(+) lymphocytes during acclimation. Furthermore, there was no increased cellular heat tolerance during secondary ex vivo heat shock of the lymphocytes acquired from subjects during acclimation. There was no effect of a mild sleep loss on any variable. We conclude that our protocol successfully induced physiological acclimation without induction of cellular heat shock responses in lymphocytes and that added mild sleep loss is not sufficient to induce a heat shock response.

The purpose of this study was to determine the effects of dehydration at a controlled relative intensity on physiological responses and trail running speed. Using a randomized, controlled crossover design in a field setting, 14 male and female competitive, endurance runners aged 30 ± 10.4 years completed 2 (hydrated [HY] and dehydrated [DHY]) submaximal trail runs in a warm environment. For each trial, the subjects ran 3 laps (4 km per lap) on trails with 4-minute rests between laps. The DHY were fluid restricted 22 hours before the trial and during the run. The HY arrived euhydrated and were given water during rest breaks. The subjects ran at a moderate pace matched between trials by providing pacing feedback via heart rate (HR) throughout the second trial. Gastrointestinal temperature (T(GI)), HR, running time, and ratings of perceived exertion (RPE) were monitored. Percent body mass (BM) losses were significantly greater for DHY pretrial (-1.65 ± 1.34%) than for HY (-0.03 ± 1.28%; p < 0.001). Posttrial, DHY BM losses (-3.64 ± 1.33%) were higher than those for HY (-1.38 ± 1.43%; p < 0.001). A significant main effect of T(GI) (p = 0.009) was found with DHY having higher T(GI) postrun (DHY: 39.09 ± 0.45°C, HY: 38.71 ± 0.45°C; p = 0.030), 10 minutes post (DHY: 38.85 ± 0.48°C, HY: 38.46 ± 0.46°C; p = 0.009) and 30 minutes post (DHY: 38.18 ± 0.41°C, HY: 37.60 ± 0.25°C; p = 0.000). The DHY had slower run times after lap 2 (p = 0.019) and lap 3 (p = 0.025). The DHY subjects completed the 12-km run 99 seconds slower than the HY (p = 0.027) subjects did. The RPE in DHY was slightly higher than that in HY immediately postrun (p = 0.055). Controlling relative intensity in hypohydrated runners resulted in slower run times, greater perceived effort, and elevated T(GI), which is clinically meaningful for athletes using HR as a gauge for exercise effort and performance.

Context: Authors of most field studies have not observed decrements in physiologic function and performance with increases in dehydration, although authors of well-controlled laboratory studies have consistently reported this relationship. Investigators in these field studies did not control exercise intensity, a known modulator of body core temperature., Objective: To directly examine the effect of moderate water deficit on the physiologic responses to various exercise intensities in a warm outdoor setting., Design: Semirandomized, crossover design., Setting: Field setting., Patients or Other Participants: Seventeen distance runners (9 men, 8 women; age = 27 +/- 7 years, height = 171 +/- 9 cm, mass = 64.2 +/- 9.0 kg, body fat = 14.6% +/- 5.5%)., Intervention(s): Participants completed four 12-km runs (consisting of three 4-km loops) in the heat (average wet bulb globe temperature = 26.5 degrees C): (1) a hydrated, race trial (HYR), (2) a dehydrated, race trial (DYR), (3) a hydrated, submaximal trial (HYS), and (4) a dehydrated, submaximal trial (DYS)., Main Outcome Measure(s): For DYR and DYS trials, dehydration was measured by body mass loss. In the submaximal trials, participants ran at a moderate pace that was matched by having them speed up or slow down based on pace feedback provided by researchers. Intestinal temperature was recorded using ingestible thermistors, and participants wore heart rate monitors to measure heart rate., Results: Body mass loss in relation to a 3-day baseline was greater for the DYR (-4.30% +/- 1.25%) and DYS trials (-4.59% +/- 1.32%) than for the HYR (-2.05% +/- 1.09%) and HYS (-2.0% +/- 1.24%) trials postrun (P < .001). Participants ran faster for the HYR (53.15 +/- 6.05 minutes) than for the DYR (55.7 +/- 7.45 minutes; P < .01), but speed was similar for HYS (59.57 +/- 5.31 minutes) and DYS (59.44 +/- 5.44 minutes; P > .05). Intestinal temperature immediately postrun was greater for DYR than for HYR (P < .05), the only significant difference. Intestinal temperature was greater for DYS than for HYS postloop 2, postrun, and at 10 and 20 minutes postrun (all: P < .001). Intestinal temperature and heart rate were 0.22 degrees C and 6 beats/min higher, respectively, for every additional 1% body mass loss during the DYS trial compared with the HYS trial., Conclusions: A small decrement in hydration status impaired physiologic function and performance while trail running in the heat.

Context: Previous researchers have not investigated the thermoregulatory responses to multiple consecutive days of American football in adolescents., Objective: To examine the thermoregulatory and hydration responses of high school players during formal preseason football practices., Design: Observational study., Setting: Players practiced outdoors in late August once per day on days 1 through 5, twice per day on days 6 and 7, and once per day on days 8 through 10. Maximum wet bulb globe temperature averaged 23 +/- 4 degrees C., Patients or Other Participants: Twenty-five heat-acclimatized adolescent boys (age = 15 +/- 1 years, height = 180 +/- 8 cm, mass = 81.4 +/- 15.8 kg, body fat = 12 +/- 5%, Tanner stage = 4 +/- 1)., Main Outcome Measure(s): We observed participants within and across preseason practices of football. Measures included gastrointestinal temperature (T(GI)), urine osmolality, sweat rate, forearm sweat composition, fluid consumption, testosterone to cortisol ratio, perceptual measures of thirst, perceptual measures of thermal sensation, a modified Environmental Symptoms Questionnaire, and knowledge questionnaires assessing the participants' understanding of heat illnesses and hydration. Results were analyzed for differences across time and were compared between younger (14-15 years, n = 13) and older (16-17 years, n = 12) participants., Results: Maximum daily T(GI) values remained less than 40 degrees C and were correlated with maximum wet bulb globe temperature (r = 0.59, P = .009). Average urine osmolality indicated that participants generally experienced minimal to moderate hypohydration before (881 +/- 285 mOsmol/kg) and after (856 +/- 259 mOsmol/kg) each practice as a result of replacing approximately two-thirds of their sweat losses during exercise but inadequately rehydrating between practices. Age did not affect most variables; however, sweat rate was lower in younger participants (0.6 +/- 0.2 L/h) than in older participants (0.8 +/- 0.1 L/h) (F(1,18) = 8.774, P = .008)., Conclusions: Previously heat-acclimatized adolescent boys (T(GI) < 40 degrees C) can safely complete the initial days of preseason football practice in moderate environmental conditions using well-designed practice guidelines. Adolescent boys replaced most sweat lost during practice but remained mildly hypohydrated throughout data collection, indicating inadequate hydration habits when they were not at practice.

Context: The protective equipment worn during American football has been shown to increase thermal strain; however, the perception of this increased heat has not been examined., Objective: To evaluate perceptual responses of American football players while wearing different uniforms during exercise in the heat and to evaluate how these responses may be used to monitor athlete safety., Design: Randomized controlled trial., Setting: Human Performance Laboratory., Patients or Other Participants: Ten men with more than 3 years of competitive experience as football linemen (age = 23.8 +/- 1.3 years, height = 183.9 +/- 1.8 cm, mass = 117.4 +/- 3.5 kg, body fat = 30.1% +/- 1.7%) participated., Intervention(s): On 3 occasions in hot, humid (33 degrees C, 48%-49% relative humidity) environmental conditions, participants completed 10 minutes of strenuous repetitive box lifting (RBL), 10 minutes of seated rest, and up to 60 minutes of treadmill walking. At each trial, they wore a different uniform condition: control (CON) clothing comprising shorts, socks, and sneakers; partial (PART) National Football League (NFL) uniform comprising the uniform without helmet or shoulder pads; or full (FULL) NFL uniform. Exercise, meals, and hydration status were controlled., Main Outcome Measure(s): Rectal temperature (T(re)), skin temperature (T(sk)), rating of perceived exertion (RPE), thermal perception (THM), perception of thirst (TST), and perception of muscle pain (MPN) were obtained for time points matched across trials., Results: Nineteen of the 30 trials ended before 60 minutes of treadmill walking as a result of participant exhaustion. Mean treadmill time was longer for the CON condition (51.7 +/- 13.4 minutes) than for the PART (43.1 +/- 15.6 minutes; t(9) = 3.092, P = .01) or the FULL (36.2 +/- 13.2 minutes; t(9) = 4.393, P = .002) conditions. Neck and forearm T(sk) increased between the initial time point and the end of exercise in the PART (33.6 +/- 0.9 degrees C and 35.0 +/- 0.6 degrees C, respectively; F(2,18) = 9.034, P < .001) and the FULL (33.4 +/- 0.9 degrees C and 35.2 +/- 0.6 degrees C, respectively; F(2,18) = 21.011, P = .002) conditions. Rate of T(re) rise was greater in the FULL (0.042 +/- 0.010 degrees C/min) than in the PART (0.034 +/- 0.006 degrees C/min) condition (F(2,27) = 10.69, P = .04). We found a relationship at the post-RBL and final time points between RPE and THM (r = 0.75, P < .001 and r = 0.59, P < .001, respectively), RPE and TST (r = 0.76, P < .001 and r = 0.61, P < .001, respectively), and RPE and MPN (r = 0.63, P < .001 and r = 0.64, P < .001, respectively). The RPE was greater at the end of exercise in the PART (17 +/- 2) and FULL (18 +/- 1) conditions than in the CON (15 +/- 3) condition (F(2,18) = 7.403, P = .005)., Conclusions: Although no differences in perceptual scales existed between the PART and FULL conditions, the T(sk) and rate of T(re) increase differed, indicating that football athletes find it difficult to perceptually rate exercise conditions as potentially dangerous hyperthermia develops. In addition, correlations between the perceptual scales further defined perceptual responses during exercise in the heat.

The purpose of this research was to characterize the movement of ingested water through body fluids, during exercise-heat stress. Deuterium oxide ((2)H(2)O) accumulation in plasma and eccrine sweat was measured at two sites (back and forehead). The exercise of 14 males was controlled via cycle ergometry in a warm environment (60 min; 28.7 degrees C, 51%rh). Subjects consumed (2)H(2)O (0.15 mg kg(-1), 99.9% purity) mixed in flavored, non-caloric, colored water before exercise, then consumed 3.0 ml kg(-1) containing no (2)H(2)O every 15 min during exercise. We hypothesized that water transit from mouth to skin would occur before 15 min. (2)H(2)O appeared rapidly in both plasma and sweat (P < 0.05), within 10 min of water consumption. The ratio (2)H(2)O/H(2)O (D:H) was 47.3-55.0 times greater in plasma than in back sweat at minutes 10, 20, and 30 (DeltaD:H relative to baseline). At elapsed minute 20, the mean rate of deuterium accumulation (DeltaD:H min(-1)) in plasma was 14.9 and 23.7 times greater than in forehead and back sweat samples, respectively. Mean (+/-SE) whole-body sweat rate was 1.04 +/- 0.05 L h(-1) and subjects with the greatest whole-body sweat rate exhibited the greatest peak deuterium enrichment in sweat (r(2) = 0.87, exponential function); the peak (2)H(2)O enrichment in sweat was not proportional (P > 0.05) to body mass, volume of the deuterium dose, or total volume of fluid consumed. These findings clarify the time course of fluid movement from mouth to eccrine sweat glands, and demonstrate considerable differences of (2)H(2)O enrichment in plasma versus sweat.

Context: When assessing exercise hyperthermia outdoors, the validity of certain commonly used body temperature measuring devices has been questioned. A controlled laboratory environment is generally less influenced by environmental factors (eg, ambient temperature, solar radiation, wind) than an outdoor setting. The validity of these temperature measuring devices in a controlled environment may be more acceptable., Objective: To assess the validity and reliability of commonly used temperature devices compared with rectal temperature in individuals exercising in a controlled, high environmental temperature indoor setting and then resting in a cool environment., Design: Time series study., Setting: Laboratory environmental chamber (temperature = 36.4 +/- 1.2 degrees C [97.5 +/- 2.16 degrees F], relative humidity = 52%) and cool laboratory (temperature = approximately 23.3 degrees C [74.0 degrees F], relative humidity = 40%)., Patients or Other Participants: Fifteen males and 10 females., Intervention(s): Rectal, gastrointestinal, forehead, oral, aural, temporal, and axillary temperatures were measured with commonly used temperature devices. Temperature was measured before and 20 minutes after entering the environmental chamber, every 30 minutes during a 90-minute treadmill walk in the heat, and every 20 minutes during a 60-minute rest in mild conditions. Device validity and reliability were assessed with various statistical measures to compare the measurements using each device with rectal temperature. A device was considered invalid if the mean bias (average difference between rectal and device temperatures) was more than +/-0.27 degrees C (+/-0.50 degrees F)., Main Outcome Measure(s): Measured temperature from each device (mean and across time)., Results: The following devices provided invalid estimates of rectal temperature: forehead sticker (0.29 degrees C [0.52 degrees F]), oral temperature using an inexpensive device (-1.13 degrees C [-2.03 degrees F]), temporal temperature measured according to the instruction manual (-0.87 degrees C [-1.56 degrees F]), temporal temperature using a modified technique (-0.63 degrees C [-1.13 degrees F]), oral temperature using an expensive device (-0.86 degrees C, [-1.55 degrees F]), aural temperature (-0.67 degrees C, [-1.20 degrees F]), axillary temperature using an inexpensive device (-1.25 degrees C, [-2.24 degrees F]), and axillary temperature using an expensive device (-0.94 degrees F [-1.70 degrees F]). Measurement of intestinal temperature (mean bias of -0.02 degrees C [-0.03 degrees F]) was the only device considered valid. Devices measured in succession (intestinal, forehead, temporal, and aural) showed acceptable reliability (all had a mean bias = 0.09 degrees C [0.16 degrees F] and r >or= 0.94])., Conclusions: Even during laboratory exercise in a controlled environment, devices used to measure forehead, temporal, oral, aural, and axillary body sites did not provide valid estimates of rectal temperature. Only intestinal temperature measurement met the criterion. Therefore, we recommend that rectal or intestinal temperature be used to assess hyperthermia in individuals exercising indoors in the heat.

This investigation evaluated the effects of a nutritional supplement (the organic osmolyte betaine) in rehydration solutions, with and without carbohydrate and electrolytes. Ten male runners ((mean +/- SD) age, 20 +/- 2 years; weight, 70.6 +/- 6.8 kg; maximal aerobic power, 63.5 +/- 4.1 mL O2 x kg(-1) x min(-1)) dehydrated to -2.7% of body weight. They next rehydrated to -1.4% of body weight by consuming 1 L fluid during each of four experiments (double-blind, randomized, cross-over design): flavored, non-caloric water (W); W + 5 g x L(-1) betaine (W+B); 6% carbohydrate-electrolyte fluid (C); or C + 5 g x L(-1) betaine (C+B). Subjects then performed prolonged treadmill running (75 minutes at 65%Vo2max) plus a performance sprint to volitional exhaustion (3.1-3.8 minutes at 84%Vo2max) in an environmental chamber (31.1 degrees C, 88.0 degrees F). Only W versus W+B and C versus C+B statistical comparisons were germane to the research questions. Observations indicated that rehydration with fluids containing betaine resulted in significant differences (p < 0.05) of plasma volume, oxygen consumption, plasma lactate concentration, and thermal sensation. The present experiments did not support the use of betaine to improve sprint duration, but nonsignificant trends occurred when betaine trials were compared with non-betaine trials (mean C+B > C by 32 seconds, +16%; mean W+B > W by 38 seconds, +21%). We interpret the increases of both aerobic and anaerobic metabolism (C+B > C) to mean that further investigation of betaine as a nutritional supplement, using other types of exercise, is warranted.

Context: Rectal temperature is recommended by the National Athletic Trainers' Association as the criterion standard for recognizing exertional heat stroke, but other body sites commonly are used to measure temperature. Few authors have assessed the validity of the thermometers that measure body temperature at these sites in athletic settings., Objective: To assess the validity of commonly used temperature devices at various body sites during outdoor exercise in the heat., Design: Observational field study., Setting: Outdoor athletic facilities., Patients or Other Participants: Fifteen men and 10 women (age = 26.5 +/- 5.3 years, height = 174.3 +/- 11.1 cm, mass = 72.73 +/- 15.95 kg, body fat = 16.2 +/- 5.5%)., Intervention(s): We simultaneously tested inexpensive and expensive devices orally and in the axillary region, along with measures of aural, gastrointestinal, forehead, temporal, and rectal temperatures. Temporal temperature was measured according to the instruction manual and a modified method observed in medical tents at local road races. We also measured forehead temperatures directly on the athletic field (other measures occurred in a covered pavilion) where solar radiation was greater. Rectal temperature was the criterion standard used to assess the validity of all other devices. Subjects' temperatures were measured before exercise, every 60 minutes during 180 minutes of exercise, and every 20 minutes for 60 minutes of postexercise recovery. Temperature devices were considered invalid if the mean bias (average difference between rectal temperature and device temperature) was greater than +/-0.27 degrees C (+/-0.5 degrees F)., Main Outcome Measure(s): Temperature from each device at each site and time point., Results: Mean bias for the following temperatures was greater than the allowed limit of +/-0.27 degrees C (+/-0.5 degrees F): temperature obtained via expensive oral device (-1.20 degrees C [-2.17 degrees F]), inexpensive oral device (-1.67 degrees C [-3.00 degrees F]), expensive axillary device (-2.58 degrees C [-4.65 degrees F]), inexpensive axillary device (-2.07 degrees C [-3.73 degrees F]), aural method (-1.00 degrees C [-1.80 degrees F]), temporal method according to instruction manual (-1.46 degrees C [-2.64 degrees F]), modified temporal method (-1.36 degrees C [-2.44 degrees F]), and forehead temperature on the athletic field (0.60 degrees C [1.08 degrees F]). Mean bias for gastrointestinal temperature (-0.19 degrees C [-0.34 degrees F]) and forehead temperature in the pavillion (-0.14 degrees C [-0.25 degrees F]) was less than the allowed limit of +/-0.27 degrees C (+/-0.5 degrees F). Forehead temperature depended on the setting in which it was measured and showed greater variation than other temperatures., Conclusions: Compared with rectal temperature (the criterion standard), gastrointestinal temperature was the only measurement that accurately assessed core body temperature. Oral, axillary, aural, temporal, and field forehead temperatures were significantly different from rectal temperature and, therefore, are considered invalid for assessing hyperthermia in individuals exercising outdoors in the heat.

This study examined the effects of rehydration (Rehy) with fluids of varying tonicities and routes of administration after exercise-induced hypohydration on exercise performance, fluid regulatory hormone responses, and cardiovascular and thermoregulatory strain during subsequent exercise in the heat. On four occasions, eight men performed an exercise-dehydration protocol of approximately 185 min (33 degrees C) to establish a 4% reduction in body weight. Following dehydration, 2% of the fluid lost was replaced during the first 45 min of a 100-min rest period by one of three random Rehy treatments (0.9% saline intravenous; 0.45% saline intravenous; 0.45% saline oral) or no Rehy (no fluid) treatment. Subjects then stood for 20 min at 36 degrees C and then walked at 50% maximal oxygen consumption for 90 min. Subsequent to dehydration, plasma Na(+), osmolality, aldosterone, and arginine vasopressin concentrations were elevated (P < 0.05) in each trial, accompanied by a -4% hemoconcentration. Following Rehy, there were no differences (P > 0.05) in fluid volume restored, post-rehydration (Post-Rehy) body weight, or urine volume. Percent change in plasma volume was 5% above pre-Rehy values, and plasma Na(+), osmolality, and fluid regulatory hormones were lower compared with no fluid. During exercise, skin and core temperatures, heart rate, and exercise time were not different (P > 0.05) among the Rehy treatments. Plasma osmolality, Na(+), percent change in plasma volume, and fluid regulatory hormones responded similarly among all Rehy treatments. Neither a fluid of greater tonicity nor the route of administration resulted in a more rapid or greater fluid retention, nor did it enhance heat tolerance or diminish physiological strain during subsequent exercise in the heat.

Although endogenous and exogenous steroid hormones affect numerous physiological processes, the interactions of reproductive hormones, chronic exercise training, and heat acclimation are unknown. This investigation evaluated the responses and adaptations of 36 inactive females [age 21 +/- 3 (SD) yr] as they undertook a 7- to 8-wk program [heat acclimation and physical training (HAPT)] of indoor heat acclimation (90 min/day, 3 days/wk) and outdoor physical training (3 days/wk) while using either an oral estradiol-progestin contraceptive (ORAL, n = 15), a contraceptive injection of depot medroxyprogesterone acetate (DEPO, n = 7), or no contraceptive (EU-OV, n = 14; control). Standardized physical fitness and exercise-heat tolerance tests (36.5 degrees C, 37% relative humidity), administered before and after HAPT, demonstrated that the three subject groups successfully (P < 0.05) acclimated to heat (i.e., rectal temperature, heart rate) and improved muscular endurance (i.e., sit-ups, push-ups, 4.6-km run time) and body composition characteristics. The stress of HAPT did not disrupt the menstrual cycle length/phase characteristics, ovulation, or plasma hormone concentrations of EU-OV. No between-group differences (P > 0.05) existed for rectal and skin temperatures or metabolic, cardiorespiratory, muscular endurance, or body composition variables. A significant difference post-HAPT in the onset temperature of local sweating, ORAL (37.2 +/- 0.4 degrees C) vs. DEPO (37.7 +/- 0.2 degrees C), suggested that steroid hormones influenced this adaptation. In summary, virtually all adaptations of ORAL and DEPO were similar to EU-OV, suggesting that exogenous reproductive hormones neither enhanced nor impaired the ability of women to complete 7-8 wk of strenuous physical training and heat acclimation.

During exercise-heat stress, ad libitum drinking frequently fails to match sweat output, resulting in deleterious changes in hormonal, circulatory, thermoregulatory, and psychological status. This condition, known as voluntary dehydration, is largely based on perceived thirst. To examine the role of preexercise dehydration on thirst and drinking during exercise-heat stress, 10 healthy men (21 +/- 1 yr, 57 +/- 1 ml x kg(-1) x min(-1) maximal aerobic power) performed four randomized walking trials (90 min, 5.6 km/h, 5% grade) in the heat (33 degrees C, 56% relative humidity). Trials differed in preexercise hydration status [euhydrated (Eu) or hypohydrated to -3.8 +/- 0.2% baseline body weight (Hy)] and water intake during exercise [no water (NW) or water ad libitum (W)]. Blood samples taken preexercise and immediately postexercise were analyzed for hematocrit, hemoglobin, serum aldosterone, plasma osmolality (P(osm)), plasma vasopressin (P(AVP)), and plasma renin activity (PRA). Thirst was evaluated at similar times using a subjective nine-point scale. Subjects were thirstier before (6.65 +/- 0.65) and drank more during Hy+W (1.65 +/- 0.18 liters) than Eu+W (1.59 +/- 0.41 and 0.31 +/- 0.11 liters, respectively). Postexercise measures of P(osm) and P(AVP) were significantly greater during Hy+NW and plasma volume lower [Hy+NW = -5.5 +/- 1.4% vs. Hy+W = +1.0 +/- 2.5% (P = 0.059), Eu+NW = -0.7 +/- 0.6% (P < 0.05), Eu+W = +0.5 +/- 1.6% (P < 0.05)] than all other trials. Except for thirst and drinking, however, no Hy+W values differed from Eu+NW or Eu+W values. In conclusion, dehydration preceding low-intensity exercise in the heat magnifies thirst-driven drinking during exercise-heat stress. Such changes result in similar fluid regulatory hormonal responses and comparable modifications in plasma volume regardless of preexercise hydration state.

The purposes of this study were to characterize measures of fluid intake and perception of thirst in women over a 6-week period of exercise-heat acclimation and outdoor training and examine if this lengthy acclimation period would result in changes in fluid intake that differ from those previously reported in men utilizing a shorter acclimation protocol of 8-10 days. Voluntary water intake (11-17 degrees C) and perception of thirst were measured in a group of 5 women (21-26 yr) undergoing exercise-heat acclimation for 90 min/day, 3 days/wk (36 degrees C, rh 50-70%) and outdoor training 3 days/wk for 6 weeks. Decreased drinking during acclimation was characterized by a decrease in the number of drinks (35 +/- 10 to 17 +/- 5; p <.05), greater time to first drink (9.9 +/- 2.0 to 23.1 +/- 4.7 min; p <.05), and a decrease in total volume ingested per week (3310 +/- 810 to 1849 +/- 446 ml; p <.05) through the 6-week study. Mean perceived thirst measurements remained low and showed only slight variance (3 +/- 0.4 to 5 +/- 0.4). These observations support a psycho-physiological response pattern different than that previously observed during 8-10 day acclimation protocols in men.

Purpose: The purpose of the study was to compare the effects of a brief period (20 min) of intravenous (IV) fluid rehydration and oral (ORAL) rehydration on ratings of perceived exertion (RPE), thirst, and thermal sensation (TS) during exercise in the heat., Methods: After dehydration (-4% of body weight), eight nonacclimated highly trained cyclists (age = 24 +/- 1 yr; VO2 = 61.4 +/- 0.8 mL.kg.min-1) performed three experimental trials. Rehydration (randomized, cross-over design) included: 1) ORAL (0.45% NaCl) equal to 50% of prior dehydration; 2) IV (0.45% NaCl) equal to 50% of prior dehydration; and 3) a control (CON), no fluid trial. Subjects then cycled at 74% VO2peak until volitional exhaustion in a hot environment (37 degrees C)., Results: Central (C-), local (L-), and overall-RPE (O-RPE) were significantly higher in CON compared to ORAL and IV at minutes 5 and 15 of exercise. C-RPE responses at minute 5 of exercise were lower (P < 0.05) during ORAL compared with IV, and C-RPE and O-RPE responses at minute 15 were lower (P < 0.05) during ORAL compared with IV. TS responses during CON were higher (P < 0.05) than ORAL and IV at minute 5, and TS was higher (P < 0.05) during IV versus ORAL at minute 15. TS were significantly correlated with all RPE responses at minute 15 in all trials. Thirst ratings were lower (P < 0.05) during ORAL compared with CON and IV at minutes 0, 5, and 15., Conclusion: It was concluded that ORAL resulted in lower RPE, thirst, and TS compared with CON and IV during exercise in the heat.

Purpose: The purpose of this study was to assess whether a brief period (20 min) of intravenous (i.v.) fluid rehydration versus oral rehydration differentially affects cardiovascular, thermoregulatory, and performance factors during exhaustive exercise in the heat., Methods: Following dehydration (-4% of body weight), eight nonacclimated highly trained cyclists (age = 23.5 +/- 1.2 yr; VO2peak = 61.4 +/- 0.8 mL x kg x min(-1); body fat = 13.5 +/- 0.6%) rehydrated and then cycled at 70% VO2peak to exhaustion in 37 degrees C. Rehydration (randomized, cross-over design) included: 1) CONTROL (no fluid), 2) DRINK (oral rehydration, 0.45% NaCl) equal to 50% of prior dehydration, and 3) IV (intravenous rehydration, 0.45% NaCl), equal to 50% of prior dehydration. Thus, in the DRINK and IV treatments subjects began exercise (EX) at -2% of body weight., Results: Exercise time to exhaustion was not different (P = 0.07) between DRINK (34.9 +/- 4 min) and IV (29.5 +/- 3.5 min), but both were significantly (P < 0.05) longer than CONTROL (18.9 +/- 2.7 min). Plasma volume was better (P < 0.05) restored during IV than CONTROL and DRINK at pre-exercise and 5 min EX, but different (P < 0.05) from only CONTROL at 15 min EX. Plasma lactate during DRINK was lower (P < 0.05) than IV at 15 min EX and postexercise. Heart rate during CONTROL was greater (P < 0.05) than DRINK and IV from 0-8 min EX, and greater (P < 0.05) than DRINK from 10-14 min EX. Rectal temperature during DRINK was less (P < 0.05) than IV from 0-24 min EX. Mean weighted skin temperature during DRINK was less (P < 0.05) than IV from 4-12 min EX., Conclusions: Thus, despite no statistically significant performance differences between DRINK and IV, it appears that certain physiological parameters were better maintained in the DRINK trial, and the trend toward performance differences may be important to elite athletes.

This study compared the influence of intravenous vs. oral rehydration after exercise-induced dehydration during a subsequent 90-min exercise bout. It was hypothesized that cardiovascular, thermoregulatory, and hormonal variables would be the same between intravenous and oral rehydration because of similar restoration of plasma volume (PV) and osmolality (Osmo). Eight non-heat-acclimated men received three experimental treatments (counterbalanced design) immediately after exercise-induced dehydration (33 degrees C) to -4% body weight loss. Treatments were intravenous 0.45% NaCl (iv; 25 ml/kg), no fluid (NF), and oral saline (Oral; 25 ml/kg). After rehydration and rest (2 h total), subjects walked at 50% maximal O2 consumption for up to 90 min at 36 degrees C. The following observations were made: 1) heart rate was higher (P < 0.05) in Oral vs. iv at minutes 45, 60, and 75 of exercise; 2) rectal temperature, sweat rate, percent change in PV, and change in plasma Osmo were similar between iv and Oral; 3) change in plasma norepinephrine decreased less (P < 0.05) in Oral compared with iv at minute 45; 4) changes in plasma adrenocorticotropic hormone and cortisol were similar between iv and Oral after exercise was initiated; and 5) exercise time was similar between iv (77.4 +/- 5.4 min) and Oral (84.2 +/- 2.3 min). These data suggest that after exercise-induced dehydration, iv and Oral were equally effective as rehydration treatments. Thermoregulation, change in adrenocorticotropic hormone, and change in cortisol were not different between iv and Oral after exercise began; this is likely due to similar percent change in PV and change in Osmo.

Twenty (12 male and 8 female) tennis players from two Division I university tennis teams performed three days of round-robin tournament play (i.e., two singles tennis matches followed by one doubles match per day) in a hot environment (32.2 +/- 1.5 degrees C and 53.9 +/- 2.4% rh at 1200 hr), so that fluid-electrolyte balance could be evaluated. During singles play, body weight percentage changes were minimal and were similar for males and females (males -1.3 +/- 0.8%, females -0.7 +/- 0.8%). Estimated daily losses (mmol.day-1) of sweat sodium (Na+) and potassium (K+) (males, Na+ 158.7, K+ 31.3; females, Na+ 86.5, K+ 18.9) were met by the players' daily dietary intakes (mmol.day-1) of these electrolytes (males, Na+ 279.1 +/- 109.4, K+ 173.5 +/- 57.7; females, Na+ 178.9 +/- 68.9, K+ 116.1 +/- 37.5). Daily plasma volume and electrolyte (Na+, K+) levels were generally conserved, although, plasma [Na+] was lower (p < .05) on the morning of Day 4. This study indicated that these athletes generally maintained overall fluid-electrolyte balance, in response to playing multiple tennis matches on 3 successive days in a hot environment, without the occurrence of heat illness.

Wheelchair athletes with spinal cord injuries (WA) face challenges to thermal homeostasis, including reduced cutaneous vasoaction and sweat production. The purpose of this study was to evaluate the efficacy of local cooling to reduce heat strain in WA. Six elite, endurance-trained male WA (33 +/- 3 yr, 64 +/- 4 kg) performed three strenuous exercise tests in a hot-humid environment (32.9 +/- 0.1 degrees C, 75 +/- 3% RH) by pushing a racing chair on a stationary roller (30 min, 16.5 km.h-1, 704-766 W metabolic heat) while wearing shorts and socks. The three treatments involved an ice-packet vest (V) (0.14 m2 of skin surface), a refrigerated headpiece (H) (0.16 m2), or no cooling (C) (control). The vest and headpiece offered potential cooling of 388 W and 266 W. Mean body heat storage for trials V (117 +/- 26 W), H (117 +/- 22 W), and C (164 +/- 40 W) were statistically similar, partly because V (117 +/- 47 W) and H (75 +/- 59 W) cooled inefficiently (30 and 28%, respectively). Repeated measure ANOVA indicated no significant between-treatment differences (P > 0.05) for any variable in trials V, H, and C. We concluded that local cooling during V and H was ineffective because heat storage decreased, but was not prevented.

A tennis player's metabolism during play in a hot environment generates an abundance of heat, which is primarily eliminated from the body by evaporation of sweat. An individual's on-court rate of fluid loss will depend on the environmental conditions, intensity of play, acclimatization, aerobic fitness, hydration status, age, and gender. Unless fluid intake closely matches sweat loss, a progressive and significant body water deficit may develop that will proportionately impair cardiovascular and thermoregulatory functions. As a result, a player can experience an increase in core temperature, premature fatigue, performance decrements, and an increased potential for heat illness. Although sweat is hypotonic compared to plasma, extended tennis play, in a hot environment, can lead to sizable Na+ and Cl- losses. Also, ad libitum drinking often leads to involuntary dehydration in these conditions. Therefore, for tennis play and training in the heat, it is important to follow a hydration plan that will minimize on-court water deficits, by optimizing fluid availability, consumption, and absorption. For tennis matches greater than 1 hour in duration, a CHO-electrolyte drink (as described earlier) is the recommended on-court beverage.

This investigation examined the influence of pre-exercise hydration status, and water intake during low intensity exercise (5.6 km.h-1 at 5% gradient) in the heat (33 degrees C), on plasma testosterone (TEST), cortisol (CORT), adrenaline (A), and noradrenaline (NA) concentrations at baseline (BL), pre-exercise (PRE), and immediately (IP), 24 h (24 P), and 48 h postexercise (48 P). Ten active men participated in four experimental treatments. These treatments differed in pre-exercise hydration status [euhydrated or hypohydrated (HY, -3.8 (SD 0.7)% body mass)] and water intake during exercise (water ad libitum or no water intake during exercise, NW). There were no significant changes in TEST, CORT, or A concentrations with time (BL, PRE, IP, 24 P, and 48 P), or among treatments. However, significant increases from BL and PRE plasma NA concentrations were observed at IP during all four treatment conditions. In addition, HY+NW resulted in significantly higher plasma NA concentrations at IP compared to all other treatments. These results suggest that moderate levels of hypohydration during prolonged, low intensity exercise in the heat do not influence plasma TEST, CORT, or A concentrations. However, plasma NA appears to respond in a sensitive manner to these hydration and exercise stresses.

Heat acclimatisation/acclimation involves a complex of adaptations which includes decreased heart rate, rectal temperature, perceived exertion as well as increased plasma volume and sweat rate. These adaptations serve to reduce physiological strain, improve an athlete's ability to exercise in a hot environment, and reduce the incidence of some forms of heat illness. Few differences exist in the ability of men and women to acclimatise to heat. Typically, older runners do not perform in the heat as well as younger runners, but physical training can negate differences between these groups. Hormonal adaptations (e.g. aldosterone, vasopressin) during heat acclimatisation encourage fluid-electrolyte retention and cardiovascular stability. Athletes with high maximal aerobic power (VO2max) acclimatise to heat faster (and lose adaptations slower when they are inactive in a cool environment) than athletes with low VO2max values. Physical training in a cool environment improves physiological responses to exercise at high ambient temperatures. In attempting to optimise heat acclimatisation, athletes should maintain fluid-electrolyte balance, exercise at intensities greater than 50% VO2max for 10 to 14 days, and avoid factors (e.g. sleep loss, infectious disease) which are known to reduce heat tolerance. Once acclimatisation has been achieved, inactivity results in a decay of favourable adaptations, after only a few days or weeks.