To investigate the effects of varying levels of hypohydration on ratings of perceived exertion (RPE) during moderate and heavy submaximal exercise, and at the lactate threshold (LT) and ventilatory threshold (VT), 9 male subjects cycled under states of euhydration (EU), moderate hypohydration (MH), and severe hypohydration (SH). The desired level of hypohydration was achieved over a 36-hr period by having subjects cycle at 50% VO2max in a 38°C environment on two occasions while controlling fluid intake and diet. During submaximal exercise, oxygen uptake, ventilation, heart rate, blood lactate, and RPE were not significantly different among treatments. Hypohydration did not significantly alter LT or VT, or perceptual responses at LT or VT. It is concluded that hypohydration of up to 5.6% caused by fluid manipulation and exercise in the heat over a 36-hr period does not alter RPE or the lactate or ventilatory threshold, nor RPE at the lactate and ventilatory thresholds measured during moderate and heavy submaximal cycling in a neutral (22°C) environment.
Donald R. Dengel, Peter G. Weyand, Donna M. Black and Kirk J. Cureton
Stefan Pettersson and Christina M. Berg
Weight category athletes are known for practicing rapid weight loss before competition weigh-in. After weigh-in, athletes strive to restore euhydration and body mass through food and fluid intake. The aim of the current study was to assess prevalence of hypohydration at competition time among elite athletes’ in four different combat sports, and how water intake and timing of official weigh-in were related to hydration status. Participants were 31 taekwondo practitioners and wrestlers who performed evening weigh-in (EWI) the night before competition day and had thus time for rehydration, and 32 boxers and judokas conducting competition day morning weigh-in (MWI). In total, 32% were female. Urine specific gravity (USG) was measured by refractometry on the competition day’s first morning urine sample. Hypohydration was defined as USG ≥1.020 and serious hypohydration as USG > 1.030. Water intake was measured by means of dietary records. The prevalence of hypohydration was 89% in the morning of competition day. Serious hypohydration was also prevalent. This was found in over 50% of MWI athletes and in 42% of the EWI group. A higher water intake, from both fluids and solid foods, in the evening before competition day was not associated with a more favorable hydration status the following morning. In conclusion, neither weigh-in close to competition nor evening weigh-in with more time for rehydration seems to prevent hypohydration before competition.
Martin J. Turner and Alberto P. Avolio
International guidelines suggest limiting sodium intake to 86–100 mmol/day, but average intake exceeds 150 mmol/day. Participants in physical activities are, however, advised to increase sodium intake before, during and after exercise to ensure euhydration, replace sodium lost in sweat, speed rehydration and maintain performance. A similar range of health benefits is attributable to exercise and to reduction in sodium intake, including reductions in blood pressure (BP) and the increase of BP with age, reduced risk of stroke and other cardiovascular diseases, and reduced risk of osteoporosis and dementia. Sweat typically contains 40–60 mmol/L of sodium, leading to approximately 20–90 mmol of sodium lost in one exercise session with sweat rates of 0.5–1.5 L/h. Reductions in sodium intake of 20–90 mmol/day have been associated with substantial health benefits. Homeostatic systems reduce sweat sodium as low as 3–10 mmol/L to prevent excessive sodium loss. “Salty sweaters” may be individuals with high sodium intake who perpetuate their “salty sweat” condition by continual replacement of sodium excreted in sweat. Studies of prolonged high intensity exercise in hot environments suggest that sodium supplementation is not necessary to prevent hyponatremia during exercise lasting up to 6 hr. We examine the novel hypothesis that sodium excreted in sweat during physical activity offsets a significant fraction of excess dietary sodium, and hence may contribute part of the health benefits of exercise. Replacing sodium lost in sweat during exercise may improve physical performance, but may attenuate the long-term health benefits of exercise.
Nidia Rodriguez-Sanchez and Stuart D.R. Galloway
Dual energy x-ray absorptiometry (DXA) is a popular tool to determine body composition (BC) in athletes, and is used for analysis of fat-free soft tissue mass (FFST) or fat mass (FM) gain/loss in response to exercise or nutritional interventions. The aim of the current study was to assess the effect of exercise-heat stress induced hypohydration (HYP, >2% of body mass (BM) loss) vs. maintenance of euhydration (EUH) on DXA estimates of BC, sum of skinfolds (SF), and impedance (IMP) measurements in athletes. Competitive athletes (23 males and 15 females) recorded morning nude BM for 7 days before the first main trial. Measurements on the first trial day were conducted in a EUH condition, and again after exercise-heat stress induced HYP. On the second trial day, fluid and electrolyte losses were replaced during exercise using a sports drink. A reduction in total BM (1.6 ± 0.4 kg; 2.3 ± 0.4% HYP) and total FFST (1.3 ± 0.4 kg), mainly from trunk (1.1 ± 0.5 kg), was observed using DXA when participants were HYP, reflecting the sweat loss. Estimated fat percent increased (0.3 ± 0.3%), however, total FM did not change (0.1 ± 0.2 kg). SF and IMP declined with HYP (losses of 1.5 ± 2.9% and 1.6 ± 3% respectively) suggesting FM loss. When EUH was maintained there were no significant changes in BM, DXA estimates, or SF values pre to post exercise, but IMP still declined. We conclude that use of DXA for FFST assessment in athletes must ensure a EUH state, particularly when considering changes associated with nutritional or exercise interventions.
Yuri Hosokawa, William M. Adams and Douglas J. Casa
Context: It is unknown how valid esophageal, rectal, and gastrointestinal temperatures (TES, TRE, and TGI) compare after exercise-induced hyperthermia under different hydration states. Objective: To examine the differences between TES, TRE, and TGI during passive rest following exercise-induced hyperthermia under 2 different hydration states: euhydrated (EU) and hypohydrated (HY). Design: Randomized crossover design. Setting: Controlled laboratory setting. Participants: 9 recreationally active male participants (mean ± SD age 24 ± 4 y, height 177.3 ± 9.9 cm, body mass 76.7 ± 11.6 kg, body fat 14.7% ± 5.8%). Intervention: Participants completed 2 trials (EU and HY) consisting of a bout of treadmill exercise (a 10-min walk at 4.8-7.2 km/h at a 5% grade followed by a 20-min jog at 8.0-12.1 km/h at a 1% grade) in a hot environment (ambient temperature 39.3 ± 1.0°C, relative humidity 37.6% ± 6.0%, wet bulb globe temperature 31.3 ± 1.5°C) followed by passive rest. Main Outcome Measures: Root-mean-squared difference (RMSD) was used to compare the variance of temperature readings at corresponding time points for TRE vs TGI, TRE vs TES, and TGI vs TES in EU and HY. RMSD values were compared using 3-way repeated-measures ANOVA. Post hoc analysis of significant main effects was done using Tukey honestly significant difference with significance set at P < .05. Results: RMSD values (°C) for all device comparisons were significantly different in EU (TRE-TGI, 0.11 ± 0.12; TRE-TES, 1.58 ± 1.01; TGI-TES, 2.04 ± 1.19) than HY (TRE-TGI, 0.22 ± 0.28; TRE-TES, 1.27 ± 0.61; TGI-TES, 1.16 ± 0.76) (P < .01). Across the 45-min bout of passive rest, there were no differences in TRE, TGI, and TES between EU and HY trials (P = .468). Conclusions: During passive rest after exercise in the heat, TRE and TGI were in good agreement when tracking body temperature, with a better agreement appearing in those maintaining a state of euhydration versus those who became hypohydrated during exercise; however, this small difference does not appear to be of clinical significance. The large differences were observed when comparing TGI and TRE with TES.
Eric D.B. Goulet, Adrien De La Flore, Félix A. Savoie and Jonathan Gosselin
Hyperhydration consists in increasing total body water above euhydration level. This hydration technique has been demonstrated to improve work capacity ( Goulet et al., 2008 ) as well as cardiovascular and thermoregulatory functions ( Goulet, 2008 ), enhance orthostatic tolerance ( Easton et
Giannis Arnaoutis, Panagiotis Verginadis, Adam D. Seal, Ioannis Vogiatzis, Labros S. Sidossis and Stavros A. Kavouras
ingest less fluid than adequate to maintain euhydration, even when provided ad libitum drinking. One of the first studies to show this phenomenon was conducted by Greenleaf and Sargent. The authors termed inadequate fluid intake as voluntary dehydration ( Greenleaf & Sargent, 1965 ). In a more recent
Francesco Campa, Catarina N. Matias, Elisabetta Marini, Steven B. Heymsfield, Stefania Toselli, Luís B. Sardinha and Analiza M. Silva
categorize euhydration. Body weight was measured with a scale without shoes and wearing minimal clothes, to the nearest 0.01 kg and stature was measured to the nearest 0.1 cm with a stadiometer (Seca, Hamburg, Germany). The intraobserver technical error of measurement (TEM) and the coefficient of variation
J. Luke Pryor, Brittany Christensen, Catherine G. R. Jackson and Stephanie Moore-Reed
before testing. Participants fasted for 4 hours prior to testing, They drank 500 mL (2 cups) of water 3 hours before and 250 mL (1 cup) of water 1 hour before the testing session to ensure euhydration. Hydration was evaluated via urine refractometry and color. If urine-specific gravity was >1.025, the
Cody R. Smith, Cory L. Butts, J.D. Adams, Matthew A. Tucker, Nicole E. Moyen, Matthew S. Ganio and Brendon P. McDermott
euhydration before body mass was assessed (349KLX Digital Medical Scale; Health-O-Meter, McCook, IL). Urine specific gravity greater than 1.025 was considered hypohydrated, and participants were provided fluid until urine specific gravity was <1.025. Participants brought their own fluids for hydration during