Search Results

This study sought to (a) estimate how the duration of running influences sweat losses and contributes to the daily fluid requirement, and (b) empirically estimate the drinking rates required to prevent significant dehydration (≥2% body weight as body water). Individual sweating data and running duration were obtained from male (n = 83) and female (n = 36) runners (n = 146 total observations) performing under highly heterogeneous conditions and over a range of exercise durations (33–280 min). Running <60 min/day increased daily fluid needs by a factor of 1.3, whereas running >60 min/day increased the daily fluid need by a factor of 1.9–2.3. Running <60 min/day generally required no fluid intake to prevent significant dehydration before run completion (31/35 runners). In contrast, running >60 min/day required more than 50% replacement of sweating rates to prevent the same (65/111 runners). Overall sweat losses ranged from ∼0.2 to ∼5.0 L/day, whereas the drinking rates required to prevent significant dehydration ranged from 0 to 1.4 L/hr. The characterization of sweat losses, sweat rate, and required drinking among runners in this study indicate wide individual variability that warrants personalized hydration practices, particularly when running is prolonged (>60 min) and performance is important. This study may serve as a useful guidepost for sports dietitians when planning and communicating fluid needs to athletes, as well as complement guidance related to both personalized programmed and thirst-driven drinking strategies.

We examined the effect of body water deficits on standing balance and sought to determine if plasma hyperosmolality (P_osm) and/or volume reduction (%ΔV_plasma) 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 V_plasma loss nor P_osm increases were associated with changes in balance. We concluded that standing balance was not altered by hypohydration.

This study assessed the plasma glucose (PG) and hormonal responses to carbohydrate ingestion, prior to exercise in the heat, in a hypohydrated state versus partial rehydration with intravenous solutions. On separate days, 8 subjects (21.0 ± 1.8 years; 57.3 ± 3.7 ml · kg⁻¹ · min⁻¹) exercised at 50% V̇O_2maxin a 33 °C environment until a 4% body weight loss was achieved. Following this, subjects were rehydrated (25 ml · kg⁻¹) with either: 0.45% IV saline (45IV), 0.9% IV saline (9IV), or no fluid (NF). Subjects then ingested 1 g · kg⁻¹ of carbohydrate and underwent an exercise test (treadmill walking, 50% V̇O_2max, 36 °C) for up to 90 min. Compared to pre-exercise level (294 mg · dl⁻¹), PG increased significantly (>124 mg · dl⁻¹) at 15 min of the exercise test in all trials and remained significantly elevated for 75 min in NF, 30 min more than in the 2 rehydration trials. Although serum Insulin increased significantly at 15 min of exercise in the 45IV trial (7.2 ± 1.2 vs. 23.7 ± 4.7 μIU · ml⁻¹) no significant differences between trials were observed. Peak plasma norepinephrine was significantly higher in NF (640 ± 66 pg · ml⁻¹) compared to the 45IV and 9IV trials (472 ± 55 and 474 ± 52 pg · ml⁻¹, respectively). In conclusion, ingestion of a small solid carbohydrate load prior to exercise in the 4% hypohydration level resulted in prolonged high PG concentration compared to partial IV rehydration.

Heat acclimation (HA) reportedly conveys conservation in sweat micromineral concentrations when sampled from arm sweat, but time course is unknown. The observation that comprehensive cleaning of the skin surface negates sweat micromineral reductions during prolonged sweating raises the question of whether the reported HA effect is real or artifact of surface contamination.

This investigation sought to study changes in leukocyte subsets after an acute bout of resistance exercise (ARE) and to determine whether ingestion of carbohydrate (CHO) could attenuate those immune responses. Nine male track-and-field athletes (21.1 ± 1.4 yr, 177.2 ± 5.5 cm, 80.9 ± 9.7 kg, 8.7% ± 3.8% fat) and 10 male ice hockey athletes (21.0 ± 2.2 yr, 174.3 ± 6.2 cm, 79.6 ±11.1 kg, 13.9% ± 3.73% fat) participated in 2 different ARE protocols. Both experiments employed a counterbalanced double-blind research design, wherein participants consumed either a CHO (1 g/kg body weight) or placebo beverage before, during, and after a weight-lifting session. Serum cortisol decreased (p < .05) at 90 min into recovery compared with immediately postexercise. Plasma lactate, total leukocyte, neutrophil, and monocyte concentrations increased (p < .05) from baseline to immediately postexercise. Lymphocytes decreased significantly (p < .05) from baseline to 90 min postexercise. Lymphocytes were lower (p < .05) for the CHO condition than for placebo. The findings of this study indicate the following: ARE appears to evoke changes in immune cells similar to those previously reported during endurance exercise, and CHO ingestion attenuates lymphocytosis after ARE.

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 ± $1.5{}^{°}\text{C}$ 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 · ${\text{day}}^{-1}$ ) of sweat sodium (Na⁺) and potassium (K⁺) (males, ${\text{Na}}^{+}$ 158.7, ${\text{K}}^{+}$ 31.3; females, ${\text{Na}}^{+}$ 86.5, ${\text{K}}^{+}$ 18.9) were met by the players' daily dietary intakes (mmol · ${\text{day}}^{-1}$ ) of these electrolytes (males, ${\text{Na}}^{+}$ 279.1 ± 109.4, ${\text{K}}^{+}$ 173.5 ± 57.7; females, ${\text{Na}}^{+}$ 178.9 ± 68.9, ${\text{K}}^{+}$ 116.1 ± 37.5). Daily plasma volume and electrolyte (Na⁺, ${\text{K}}^{+}$ ) 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.