Sensory Perception of an Oral Rehydration Solution during Exercise in the Heat

Prolonged exercise in the heat elicits a number of physiological changes as glycogen stores are low and water and electrolytes are lost through sweat. However, it is unclear whether these changes provoke an increase in liking of saltiness and, therefore, palatability of an oral rehydration solution (ORS). Twenty-seven recreationally active participants (n = 13 males; n = 14 females) completed sensory analysis of an ORS, a traditional sports drink (TS), and a flavored water placebo (PL) at rest and during 60 min (3 × 20-min bouts) of cycling exercise at 70% age-predicted maximum heart rate (HR_max) at 35.3 ± 1.4 °C and 41 ± 6% relative humidity. Before and after every 20 min of exercise, drinks were rated (using 20-mL beverage samples) based on liking of sweetness, liking of saltiness, thirst-quenching ability, and overall liking on a nine-point hedonic scale. Hydration status was assessed by changes in semi-nude body mass, saliva osmolality (S_Osm), and saliva total protein concentration (S_PC). After 60 min of exercise, participants lost 1.36 ± 0.39% (mean ± SD) of body mass and there were increases in S_Osm and S_PC. At all time points, liking of sweetness, saltiness, thirst-quenching ability, and overall liking was higher for the TS and PL compared to the ORS (p < 0.05). However, the saltiness liking and thirst-quenching ability of the ORS increased after 60 min of exercise compared to before exercise (p < 0.05). There was also a change in predictors of overall liking with pre-exercise ratings mostly determined by liking of sweetness, saltiness, and thirst-quenching ability (p < 0.001), whereas only liking of saltiness predicted overall liking post-exercise (R² = 0.751; p < 0.001). There appears to be a hedonic shift during exercise in which the perception of saltiness becomes the most important predictor of overall liking. This finding supports the potential use of an ORS as a valuable means of hydration during the latter stages of prolonged and/or intense exercise in the heat.

Postexercise rehydration: potassium-rich drinks versus water and a sports drink

Fluid retention, thirst quenching, tolerance, and palatability of different drinks were assessed. On 4 different days, 12 healthy, physically active volunteers (24.4 ± 3.2 years old, 74.75 ± 11.36 kg body mass (mean ± S.D)), were dehydrated to 2.10% ± 0.24% body mass by exercising in an environmental chamber (32.0 ± 0.4 °C dry bulb, 53.8 ± 5.2% relative humidity). Each day they drank 1 of 4 beverages in random order: fresh coconut water (FCW), bottled water (W), sports drink (SD), or potassium-rich drink (NEW); volume was 120% of weight loss. Urine was collected and perceptions self-reported for 3 h. Urine output was higher (p < 0.05) for W (894 ± 178 mL) than SD (605 ± 297 mL) and NEW (599 ± 254 mL). FCW (686 ± 250 mL) was not different from any other drink (p > 0.05). Fluid retention was higher for SD than W (68.2% ± 13.0% vs. 51.3% ± 12.6%, p = 0.013), but not for FCW and NEW (62.5% ± 15.4% and 65.9% ± 15.4%, p > 0.05). All beverages were palatable and well tolerated; none maintained a positive net fluid balance after 3 h, but deficit was greater in W versus SD (p = 0.001). FCW scored higher for sweetness (p = 0.03). Thirst increased immediately after exercise but returned to baseline after drinking a small volume (p < 0.0005). In conclusion, additional potassium in FCW and NEW did not result in additional rehydration benefits over those already found in a conventional sports drink with sodium.