Rehydration during exercise in the heat reduces physiological strain index in healthy adults

Abstract

Exercise in the heat leads to physiological alterations that reflect mainly on the cardiovascular system. The physiological strain index (PSI) uses heart rate (HR) and rectal temperature (Tre) to evaluate the cardiovascular strain and lately it has been brought up on the literature. However, few studies used the PSI to evaluate its response following dehydration and rehydration protocols. Thus, the aim of the present study was to verify the effect of rehydration proportional to fluid losses during prolonged exercise in the heat on hydration status, PSI and rating of perceived exertion (RPE) in healthy subjects. Ten volunteers performed two sessions of exercise in heat. The first with fluid restriction until subjects reach 2% of body mass (BM) reduction. The second with rehydration proportional to fluid losses of the first. HR and Tre were monitored during the entire exercise protocol in order to calculate PSI. Subjects also reported their RPE. BM, urine specific gravity (USG) and urine color (UC) were measured to evaluate hydration status. Results demonstrated greater PSI in the fluid restricted trial compared to the rehydration trial from 45 minutes of exercise (p<0,05), and that differences remain significant until the end of the protocol. RPE also presented significant differences between trials (p<0,001). Rehydration strategy was effective to maintain hydration status and attenuate the increase on PSI and RPE, which has important implications for sports, especially those with more than 45 minutes