This study investigated the effects of progressive mild dehydration during cycling on whole-body substrate oxidation and skeletal-muscle metabolism in recreationally active men. Subjects (N = 9) cycled for 120 min at ~65% peak oxygen uptake (VO2peak 22.7 °C, 32% relative humidity) with water to replace sweat losses (HYD) or without fluid (DEH). Blood samples were taken at rest and every 20 min, and muscle biopsies were taken at rest and at 40, 80, and 120 min of exercise. Subjects lost 0.8%, 1.8%, and 2.7% body mass (BM) after 40, 80, and 120 min of cycling in the DEH trial while sweat loss was not significantly different between trials. Heart rate was greater in the DEH trial from 60 to 120 min, and core temperature was greater from 75 to 120 min. Rating of perceived exertion was higher in the DEH trial from 30 to 120 min. There were no differences in VO2, respiratory-exchange ratio, total carbohydrate (CHO) oxidation (HYD 312 ± 9 vs. DEH 307 ± 10 g), or sweat rate between trials. Blood lactate was significantly greater in the DEH trial from 20 to 120 min with no difference in plasma free fatty acids or epinephrine. Glycogenolysis was significantly greater (24%) over the entire DEH vs. HYD trial (433 ± 44 vs. 349 ± 27 mmol · kg−1 · dm−1). In conclusion, dehydration of <2% BM elevated physiological parameters and perceived exertion, as well as muscle glycogenolysis, during exercise without affecting whole-body CHO oxidation.
Heather M. Logan-Sprenger, George J. F. Heigenhauser, Graham L. Jones and Lawrence L. Spriet
Cyril Schmit, Rob Duffield, Christophe Hausswirth, Jeanick Brisswalter and Yann Le Meur
.7 (1.6) Abbreviations: BML, body-mass loss; C, control; HA-H, heat acclimation at high exercise intensity; HA-L, heat acclimation at low exercise intensity; HR, heart rate; max, maximum; RPE, rating of perceived exertion; T core , core temperature; TT, time trial; WU, warm-up; AU, arbitrary units. Note
Joseph F. Seay, Brett R. Ely, Robert W. Kenefick, Shane G. Sauer and Samuel N. Cheuvront
We examined the effect of body water deficits on standing balance and sought to determine if plasma hyperosmolality (Posm) and/or volume reduction (%ΔVplasma) exerted independent effects. Nine healthy volunteers completed three experimental trials which consisted of a euhydration (EUH) balance test, a water deficit session and a hypohydration (HYP) balance test. Hypohydration was achieved both by exercise-heat stress to 3% and 5% body mass loss (BML), and by a diuretic to 3% BML. Standing balance was assessed during quiet standing on a force platform with eyes open and closed. With eyes closed, hypohydration significantly decreased medial-lateral sway path and velocity by 13% (both p < .040). However, 95% confidence intervals for the mean difference between EUH and HYP were all within the coefficient of variation of EUH measures, indicating limited practical importance. Neither Vplasma loss nor Posm increases were associated with changes in balance. We concluded that standing balance was not altered by hypohydration.
Karen Soo and Geraldine Naughton
This study investigated the hydration profile of high-performance female cricket players competing at a national tournament. The profile comprised hydration monitoring (n = 18) and a questionnaire (n = 20). Our objectives were to 1) advance the understanding of fluid losses in cricket sessions across a tournament and 2) assess the hydration knowledge and practices in female cricket players. Body mass before and after each game inning was recorded in order to estimate sweat rate, sweat loss, and percentage body-mass loss. Comparisons were made between groups categorized according to level of activity during each inning. When sweat rates were estimated according to actual activity time, results were in the range of those in other female team sports but less than results from male cricket players. A range of knowledge of hydration issues was also observed. This study supports the need for individualized hydration recommendations and provides direction for further hydration education in women’s cricket.
Tammie R. Ebert, David T. Martin, Brian Stephens, Warren McDonald and Robert T. Withers
To quantify the fluid and food consumed during a men’s and women’s professional road-cycling tour.
Eight men (age 25 ± 5 y, body mass ± 7.4 kg, and height 177.4 ± 4.5 cm) and 6 women (age 26 ± 4 y, body mass ± 5.6 kg, and height 170.4 ± 5.2 cm) of the Australian Institute of Sport Road Cycling squads participated in the study. The men competed in the 6-d Tour Down Under (Adelaide, Australia), and the women, in the 10-d Tour De L’Aude (Aude, France). Body mass was recorded before and immediately after the race. Cyclists recalled the number of water bottles and amount of food they had consumed.
Men and women recorded body-mass losses of ~2 kg (2.8% body mass) and 1.5 kg (2.6% body mass), respectively, per stage during the long road races. Men had an average fluid intake of 1.0 L/h, whereas women only consumed on average 0.4 L/h. In addition, men consumed CHO at the rate suggested by dietitians (average CHO intake of 48 g/h), but again the women failed to reach recommendations, with an average intake of ~21 g/h during a road stage.
Men appeared to drink and eat during racing in accordance with current nutritional recommendations, but women failed to reach these guidelines. Both men and women finished their races with a body-mass loss of ~2.6% to 2.8%. Further research is required to determine the impact of this loss on road-cycling performance and thermoregulation.
Stephen A. Mears and Susan M. Shirreffs
Exercising in cold environments results in water losses, yet examination of resultant voluntary water intake has focused on warm conditions. The purpose of the study was to assess voluntary water intake during and following exercise in a cold compared with a warm environment. Ten healthy males (22 ± 2 years, 67.8 ± 7.0 kg, 1.77 ± 0.06 m, VO2peak 60.5 ± 8.9 ml·kg−1·min−1) completed two trials (7–8 days). In each trial subjects sat for 30 min before cycling at 70% VO2peak (162 ± 27W) for 60 min in 25.0 ± 0.1 °C, 50.8 ± 1.5% relative humidity (RH; warm) or 0.4 ± 1.0 °C, 68.8 ± 7.5% RH (cold). Subjects then sat for 120 min at 22.2 ± 1.2 °C, 50.5 ± 8.0% RH. Ad libitum drinking was allowed during the exercise and recovery periods. Urine volume, body mass, serum osmolality, and sensations of thirst were measured at baseline, postexercise and after 60 and 120 min of the recovery period. Sweat loss was greater in the warm trial (0.96 ± 0.18 l v 0.48 ± 0.15 l; p < .0001) but body mass losses over the trials were similar (1.15 ± 0.34% (cold) v 1.03 ± 0.26% (warm)). More water was consumed throughout the duration of the warm trial (0.81 ± 0.42 l v 0.50 ± 0.49 l; p = .001). Cumulative urine output was greater in the cold trial (0.81 ± 0.46 v 0.54 ± 0.31 l; p = .036). Postexercise serum osmolality was higher compared with baseline in the cold (292 ± 2 v 287 ± 3 mOsm.kg−1, p < .0001) and warm trials (288 ± 5 v 285 ± 4 mOsm·kg−1; p = .048). Thirst sensations were similar between trials (p > .05). Ad libitum water intake adjusted so that similar body mass losses occurred in both trials. In the cold there appeared to a blunted thirst response.
Martin D. Hoffman, Kristin J. Stuempfle, Ian R. Rogers, Louise B. Weschler and Tamara Hew-Butler
To determine the incidence of exercise-associated hyponatremia (EAH), the associated biochemical measurements and risk factors for EAH, and whether there is an association between postrace blood sodium concentration ([Na+]) and changes in body mass among participants in the 2009 Western States Endurance Run, a 161-km mountain trail run.
Change in body mass, postrace [Na+], and blood creatine phosphokinase (CPK) concentration, and selected runner characteristics were evaluated among consenting competitors.
Of the 47 study participants, 14 (30%) had EAH as defined by a postrace [Na+] <135 mmol/L. Postrace [Na+] and percent change in body mass were directly related (r = .30, P = .044), and 50% of those with EAH had body mass losses of 3–6%. EAH was unrelated to age, sex, finish time, or use of nonsteroidal anti-inflammatory drugs during the run, but those with EAH had completed a smaller (P = .03) number of 161-km ultramarathons. The relationship of CPK levels to postrace [Na+] did not reach statistical significance (r = –.25, P = .097).
EAH was common (30%) among finishers of this 161-km ultramarathon and it was not unusual for those with EAH to be dehydrated. As such, changes in body mass should not be relied upon in the assessment for EAH during 161-km ultramarathons.
Ronald J. Maughan, Lisa A. Dargavel, Rachael Hares and Susan M. Shirreffs
This study investigated fluid and electrolyte balance in well-trained male and female swimmers during 2 training sessions. Participants were 17 nationally ranked swimmers measured during a period of intensive training. Sweat loss was assessed from changes in body mass after correction for fluid intake and urine collection. Sweat composition was measured from waterproof absorbent patches applied at 4 skin sites. Air and pool-water temperatures were 36 °C and 27.4 °C, respectively. Training lasted 105 min in each session. All measured variables were similar on the 2 testing days. Mean sweat-volume loss was 548 ± 243 ml, and mean sweat rate was 0.31 ± 0.1 L/hr. Mean fluid intake was 489 ± 270 ml. Mean body-mass loss was 0.10 ± 0.50 kg, equivalent to 0.1% ± 0.7% dehydration. Mean pretraining urine osmolality was 662 ± 222 mOsm/kg, which was negatively associated with both mean drink volume consumed (p = .044, r 2 = .244) and mean urine volume produced during training (p = .002, r 2 = .468). Mean sweat Na+, K+, and Cl− concentrations (mmol/L) were 43 ± 14, 4 ± 1, and 31± 9, respectively; values were not different between males and females and were not different between days except for a marginal difference in K+ concentration. The average swimmer remained hydrated during the session, and calculated sweat rates were similar to those in previous aquatic studies.
Hamish A.B. Reid, Nicholas C. Dennison, Jonathan Quayle and Tom Preston
Meeting the energy demands of prolonged arduous expeditions and endurance sport may be a significant barrier to success. Expedition rowing is associated with high levels of body-mass loss, reflecting the challenge of meeting energy expenditure in this exacting environment.
To use the doubly labeled water (DLW) technique to calculate the total energy expenditure (TEE) and body-composition changes of two 28-y-old healthy male athletes during a 50-d continuous and unsupported row around Great Britain.
A measured dose of DLW was taken at the start of 2 separate study periods (days 5–19 and 34–48) followed by sequential urine collection, which was analyzed on return to land.
Mean TEE was 15.3 MJ/d: athlete 1, 16.4 MJ/d; athlete 2, 14.9 MJ/d. Athlete 1 lost 11.2 kg and athlete 2 lost 14.9 kg of body mass during the row. Average energy provision was 19.1 MJ per 24-h ration pack.
These results highlight the difficulty of maintaining energy balance during expedition rowing. A starvation state was observed despite dietary provision in excess of estimated energy expenditure, indicating that nutritional strategy rather than caloric availability was at fault. The authors recommend that future expeditions prioritize thorough testing and the individualization of rations to ensure that they are both palatable and practical during the weeks to months at sea.
David J. Clayton, Gethin H. Evans and Lewis J. James
The purpose of this study was to examine the gastric emptying and rehydration effects of hypotonic and hypertonic glucose-electrolyte drinks after exercise-induced dehydration. Eight healthy males lost ~1.8% body mass by intermittent cycling and rehydrated (150% of body mass loss) with a hypotonic 2% (2% trial) or a hypertonic 10% (10% trial) glucose-electrolyte drink over 60 min. Blood and urine samples were taken at preexercise, postexercise, and 60, 120, 180, and 240 min postexercise. Gastric and test drink volume were determined 15, 30, 45, 60, 90, and 120 min postexercise. At the end of the gastric sampling period 0.3% (2% trial) and 42.1% (10% trial; p < .001) of the drinks remained in the stomach. Plasma volume was lower (p < .01) and serum osmolality was greater (p < .001) at 60 and 120 min during the 10% trial. At 240 min, 52% (2% trial) and 64% (10% trial; p < .001) of the drinks were retained. Net fluid balance was greater from 120 min during the 10% trial (p < .001). When net fluid balance was corrected for the volume of fluid in the stomach, it was greater at 60 and 120 min during the 2% trial (p < .001). These results suggest that the reduced urine output following ingestion of a hypertonic rehydration drink might be mediated by a slower rate of gastric emptying, but the slow gastric emptying of such solutions makes rehydration efficiency difficult to determine in the hours immediately after drinking, compromising the calculation of net fluid balance.