Impact of dehydration on perceived exertion during endurance exercise: A systematic review with meta-analysis

BACKGROUND: Understanding the impact of stressors on the rating of perceived exertion (RPE) is relevant from a performance and exercise adherence/participation standpoint. Athletes and recreationally active individuals dehydrate during exercise. No attempt has been made to systematically determine the impact of exercise-induced dehydration (EID) on RPE. OBJECTIVE: The present meta-analysis aimed to determine the effect of EID on RPE during endurance exercise and examine the moderating effect of potential confounders. DATA ANALYSES: Performed on raw RPE values using random-effects models weighted mean effect summaries and meta-regressions with robust standard errors, and with a practical meaningful effect set at 1 point difference between euhydration (EUH) and EID. Only controlled crossover studies measuring RPE with a Borg scale in healthy adults performing ≥30 min of continuous endurance exercise while dehydrating or drinking to maintain EUH were included. RESULTS: Sixteen studies were included, representing 147 individuals. Mean body mass loss with EUH was 0.5 ± 0.4%, compared to 2.3 ± 0.5% with EID (range 1.7–3.1%). Within an EID of 0.5–3% body mass, a maximum difference in RPE of 0.81 points (95% CI: 0.36–1.27) was observed between conditions. A meta-regression revealed that RPE increases by 0.21 points for each 1% increase in EID (95% CI: 0.12–0.31). Humidity, ambient temperature and aerobic capacity did not alter the relationship between EID and RPE. CONCLUSION: Therefore, the effect of EID on RPE is unlikely to be practically meaningful until a body mass loss of at least 3%.