Effect of breathing cooled air during cycling on physiology and performance in the heat.

BACKGROUND: The aim of this study was to determine the physiological, perceptual, and exercise performance responses to breathing cooled air during and following exercise in the heat. METHODS: Twelve trained male cyclists (26±4 y; 180.5±5.6 cm; 56.4±7.5 mL/kg/min V̇O2max) cycled at 60% V̇O2max for 75 minutes, completed a 5-kilometer (5k) time trial, and recovered for 15 minutes in hot conditions (31 °C; 55% RH). Participants completed three separate trials in random order; breathing room air at a 1:4 (1 min on: 4 min off) ratio without ice (control [CON]), a 1:4 min ratio with ice (low-dose inhalation [LO]), and 1:1 min ratio with ice (high-dose inhalation [HI]). Intestinal temperature (TGI), heart rate (HR), blood pressure (BP), thirst, thermal sensation, rating of perceived exertion (RPE), and inspired air temperature were recorded every 15 minutes during cycling and five minutes during time trial and recovery. RESULTS: TGI (P=0.827), HR (P=0.363), Physiological Strain Index ([PSI], P=0.253), mean arterial pressure ([MAP] P=0.055) and thirst sensation (P=0.140) were not different between trials. Following the time trial, thermal sensation and RPE were significantly decreased in LO vs. CON and HI vs. CON (P≤0.039). Following the cooldown, thermal sensation was significantly decreased in HI vs. CON (P=0.006). Five-k time trial differences were not significant between groups (P≥0.098). CONCLUSIONS: Breathing cooled air during cycling in the heat did not provide a significant thermoregulatory or statistically significant performance advantage.

No Change in 24-Hour Hydration Status Following a Moderate Increase in Fluid Consumption.

PURPOSE: To investigate changes in 24-hour hydration status when increasing fluid intake. METHODS: Thirty-five healthy males (age 23.8 ± 4.7 years; mass 74.0 ± 9.4 kg) were divided into 4 treatment groups for 2 weeks of testing. Volumes of 24-hour fluid ingestion (including water from food) for weeks 1 and 2 was 35 and 40 ml/kg body mass, respectively. Each treatment group was given the same proportion of beverages in each week of testing: water only (n = 10), water + caloric cola (n = 7), water + noncaloric cola (n = 10), or water + caloric cola + noncaloric cola + orange juice (n = 8). Serum osmolality (Sosm), total body water (TBW) via bioelectrical impedance, 24-hour urine osmolality (Uosm), and volume (Uvol) were analyzed at the end of each 24-hour intervention. RESULTS: Independent of treatment, total beverage consumption increased 22% from week 1 to 2 (1685 ± 320 to 2054 ± 363 ml; p < 0.001). Independent of beverage assignment, the increase in fluid consumption between weeks 1 and 2 did not change TBW (43.4 ± 5.2 vs 43.0 ± 4.8 kg), Sosm (292 ± 5 vs 292 ± 5 mOsm/kg), 24-hour Uosm (600 ± 224 vs 571 ± 212 mOsm/kg), or 24-hour Uvol (1569 ± 607 vs 1580 ± 554 ml; all p > 0.05). CONCLUSIONS: Regardless of fluid volume or beverage type consumed, measures of 24-hour hydration status did not differ, suggesting that standard measures of hydration status are not sensitive enough to detect a 22% increase in beverage consumption.

Hydration Status over 24-H Is Not Affected by Ingested Beverage Composition.

OBJECTIVE: To investigate the 24-h hydration status of healthy, free-living, adult males when given various combinations of different beverage types. METHODS: Thirty-four healthy adult males participated in a randomized, repeated-measures design in which they consumed: water only (treatment A), water+cola (treatment B), water+diet cola (treatment C), or water+cola+diet cola+orange juice (treatment D) over a sedentary 24-h period across four weeks of testing. Volumes of fluid were split evenly between beverages within each treatment, and when accounting for food moisture content and metabolic water production, total fluid intake from all sources was equal to 35 ± 1 ml/kg body mass. Urine was collected over the 24-h intervention period and analyzed for osmolality (Uosm), volume (Uvol) and specific gravity (USG). Serum osmolality (Sosm) and total body water (TBW) via bioelectrical impedance were measured after the 24-h intervention. RESULTS: 24-h hydration status was not different between treatments A, B, C, and D when assessed via Uosm (590 ± 179; 616 ± 242; 559 ± 196; 633 ± 222 mOsm/kg, respectively) and Uvol (1549 ± 594; 1443 ± 576; 1690 ± 668; 1440 ± 566 ml) (all p > 0.05). A -difference in 24-h USG was observed between treatments A vs. D (1.016 ± 0.005 vs. 1.018 ± 0.007; p = 0.049). There were no differences between treatments at the end of the 24-h with regard to Sosm (291 ± 4; 293 ± 5; 292 ± 5; 293 ± 5 mOsm/kg, respectively) and TBW (43.9 ± 5.9; 43.8 ± 6.0; 43.7 ± 6.1; 43.8 ± 6.0 kg) (all p > 0.05). CONCLUSIONS: Regardless of the beverage combination consumed, there were no differences in providing adequate hydration over a 24-h period in free-living, healthy adult males. This confirms that beverages of varying composition are equally effective in hydrating the body.

Effect of air-filled vest on exercise-heat strain when wearing ballistic protection.

OBJECTIVES: The purpose was to determine if an air-filled vest worn under ballistic protection reduces physiological strain during exercise in the heat either while wearing a tactical military (TM) protective vest or a law enforcement (LE) concealable vest. METHODS: Sixteen men (24.5±3.9 years; 179.5±5.6 cm; 84.6±12.3kg) performed either two or four trials of treadmill walking (1.34 m s(-1); 2% grade) over 120 min in a hot, dry environment (37°C, 30% relative humidity, wind speed 3.5 m s(-1)). Participants completed trials wearing a TM or LE, with either the air-filled vest (TMa; LEa) or no vest (TMc; LEc) in random order. During trials, participants wore Army Combat Uniform pants. Physiological variables measured every 5min included gastrointestinal temperature (T GI), mean skin temperature (T sk), and heart rate (HR). Sweat rate (SR) was calculated based on fluid intake and body mass measures. RESULTS: In the tactical trial (TMa versus TMc), no differences in final T GI (38.2±0.4 versus 38.3±0.4°C), T sk (35.0±0.9 versus 35.0±1.0°C), HR (142±19 versus 143±23 bpm) existed (P>0.05). In the LE trials (LEa versus LEc), no differences in final T GI (38.0±0.4 versus 38.1±0.3°C), T sk (35.3±1.1 versus 35.6±0.9°C), HR (132±20 versus 135±20 bpm) existed (P>0.05). Despite slightly higher SR, there was no statistical difference in TM (1.15±1.13 versus 1.54±0.46 l h(-1); P=0.10) or in LE (1.39±0.52 versus 1.37±0.18 l h(-1); P=0.35) during trials. CONCLUSION: When participants exercised with a TM or LE while wearing the air-filled vest, there were no thermoregulatory and physiological differences compared to control trials. In our testing conditions, the air-filled device had little effect on physiological responses during prolonged mild exercise in the heat.