Sensory perception of an oral rehydration solution throughout exercise in the heat : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Science in Nutrition and Dietetics at Massey University, Albany, New Zealand

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Background: Oral rehydration solutions (ORS) are formulated specifically to replenish fluid and electrolytes lost through diarrhoea and sweat. Regardless of poor palatability ratings in relation to traditional sports drinks or water, ORS may be effective at optimising hydration during prolonged exercise in the heat. Aim: To assess the palatability of an ORS at rest and throughout 60 min of moderate intensity exercise in the heat. Methods: Twenty-seven recreationally active participants (n=13 males; n=14 females) completed sensory analysis of an ORS, a traditional sports drink (TS) and a flavoured water placebo (PL) at rest and throughout 60 min (3 x 20-min bouts) of cycling exercise at 70% age-predicted maximum heart rate (HRmax) at 30-35°C. Before and every 20 min after exercise, drinks were rated based on liking of sweetness, liking of saltiness, thirst-quenching ability, and overall liking on a 9-point hedonic scale. Hydration status was assessed by changes in semi-nude body mass, urine osmolality (UOsm), urine specific gravity (USG), urine colour (UCol), saliva osmolality (SOsm), and saliva total protein concentration (SPC). Results: After 60 min of exercise, participants had lost an average of 1.36 ± 0.39 % of body mass and there was an increase in SOsm, SPC, USG and UCol (p<0.05) but no change in UOsm (p>0.05). 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 significantly after 60 min of exercise compared to before exercise (p<0.05). There was also a significant 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). Conclusions: 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.
dehydration, electrolytes, palatability, saltiness, sports drinks, thirst