Intermittent Cycle Sprints Following Heat Exposure with Fluid Replacement and Heat Exposure to 3% Dehydration

Abstract

Many studies have examined the influence of dehydration on anaerobic performance. However, application beyond the laboratory is complicated because most sports and strenuous jobs should not be classified solely as aerobic or anaerobic, but are a mixture of lower intensity aerobic bouts interspersed with repeated work bouts primarily dominated by anaerobic metabolism. PURPOSE: This study examined effects of heat exposure with and without dehydration on repeated anaerobic cycling. METHODS: Ten males completed three trials: a) control (CT), b) heat exposure to 3% dehydration (equal fluid volume (H2O) replaced during exposure) (HE), and c) heat exposure to 3% dehydration (no fluid replaced) (DEHY). HE and DEHY were achieved via hot water submersion (~39°C). For CT, HE, and DEHY, subjects returned to baseline core temperature and completed 6 x 15s cycle sprints with 30s active recovery. RESULTS: ANOVAs (p≤ 0.05) were applied to plasma volume (PV), mean power (MP), peak power (PP), percent decrease, seconds above 90 rev·min−1, heart rate (HR), and post-sprint RPE. Results indicated pre-sprint PV was significantly lower for DEHY (47.5 ± 4.5%) and HE (49.4 ± 2.0%) than CT (53.2 ± 2.4%). MP for DEHY (569 ± 72W) was significantly lower and the difference approached significance (p=0.07) for HE (582 ± 76W) vs. CT (596 ± 66W). PP was significantly lower for HE (870 ± 128W) and the difference approached significance (p=0.07) for DEHY (857 ± 145W) vs. CT (900 ± 117W). Post-sprint RPE was significantly higher for DEHY (6.4 ± 2.0) and HE (6.3 ± 1.6) than for CT (5.7 ± 2.1). No difference was observed among trials for percent decrease, seconds above 90 rev·min−1, or HR. Although initial sprint performances were similar among trials, performance declined most in later bouts (sprints 5 and 6: MP, PP, CT > DEHY and sprint 6: PP, CT > HE). CONCLUSIONS: Combined heat exposure and dehydration impaired sprint cycling performance (MP and PP) with HE performance intermediate to CT and DEHY. Results indicate altered fluid balance as well as heat exposure negatively affects repeated anaerobic performance with decrements magnified in later bouts.