Author(s): WANG, H., LI, H., EARLY, K. , Institution: ZHEJIANG NORMAL UNIVERSITY, Country: CHINA, Abstract-ID: 1328

INTRODUCTION:
Typically, sweat rate and sweat electrolyte losses have a large inter-individual variability and this makes specific hydration plan for a large population so difficult. However, a personalized approach to hydration can overcome this issue to meet a person’s particular fluid and sodium needs. Thus, the purpose of this research was to investigate the effects of a personalized hydration strategy (PHS) on body fluid balance and high-intensity intermittent exercise performance.
METHODS:
Twelve healthy, active participants completed a maximal oxygen consumption test (VO2max) and two 5-day trial arms. One arm was under normothermic condition (NOR; ~23°C) and the other arm was under hyperthermic condition (HYP; ~35°C). Each arm began with 3 days of familiarization exercise phase, which consisted of a 45min treadmill run at 50% VO2max. After the familiarization phase, participants randomly performed the main exercise trial with a either PHS and control (CON; day 4 and 5). The PHS was prescribed according to a participant’s fluid and sweat sodium losses during familiarization phase. CON was selected the commercially available electrolyte beverage drinking ad-libitum. The main exercise trial consisted two phases: first phase was 45min treadmill run at 50% VO2max and second phase was high-intensity intermittent exercise (HIIT) at 80%VO2max, 5% grade for 60s followed by a fast walk at 40%VO2max, 5% grade for 30s until voluntary fatigue. Fluid replacement was only allowed in the first phase of exercise trial. PHS participants drank the solution with amount equally distributed every 10min, whereas CON participants drank ad-libitum. Participants then crossed over to the second arm with a washout period of 7 days to result in the following trials: NOR+PHS, NOR+CON, HYP+PHS, and HYP+CON. Canal temperature (Tc), heart rate, thirst perception, rating of perceived exertion (RPE), and the parameters of fluid balance (sweat and urine sodium [Na+]) were assessed.
RESULTS:
In PHS trials, participants had a significantly greater fluid intake and less body mass loss compared to CON, regardless of environmental condition (all p<0.001). HYP+CON produced the lowest sweat Na+ concentration (56.2±9.0mmol/L) compared to other trials (all p<0.001). Under NOR condition, no HIIT exercise performance advantage was found in PHS. However, under HYP condition, participants in HYP+PHS had a lower RPE (9±3 vs. 10±3, p=0.03) and Tc (37.0±0.4℃ vs. 37.1±0.5°C, p=0.03) in the first phase of exercise compared to HYP+CON. HYP+PHS had the lowest thirst perception (3.6±2.4) compared to HYP+CON in the second phase (4.2±2.2, p=0.004) and HYP+PHS had a greater HIIT exercise performance (765±452s) compared to HYP+CON (548±283s, p=0.04).
CONCLUSION:
PHS reinforces fluid intake and successfully optimizes hydration status and offset sweat sodium loss, regardless of environmental conditions. However, PHS may be or is more important to prevent negative physiological consequences during high-intensity exercise in the heat.