The effects of high-intensity intermittent exercise compared with continuous exercise on voluntary water ingestion

Water intake occurs following a period of high intensity intermittent exercise (HIIE) due to sensations of thirst yet this does not always appear to be caused by body water losses. Thus, the aim was to assess voluntary water intake following HIIE. Ten healthy males (22±2y, 75.6±6.9kg, V˙O2peak 57.3±11.4ml.kg-1.min-1) (mean±SD) completed two trials (7-14d apart). Subjects sat for 30min then completed an exercise period involving 2min of rest followed by 1min at 100%V˙O2peak repeated for 60min (HIIE) or 60min continuously at 33%V˙O2peak (LO). Subjects then sat for 60min and were allowed ad libitum water intake. Body mass was measured at start and end of trials. Serum osmolality, blood lactate and sodium concentrations, sensations of thirst and mouth dryness were measured at baseline, post-exercise and after 5, 15, 30 and 60min of recovery. Vasopressin concentration was measured at baseline, post-exercise, 5 and 30min. Body mass loss over the whole trial was similar (HIIE: 0.77±0.50; LO: 0.85±0.55%) (p=0.124). Sweat lost during exercise (0.78±0.22 v 0.66±0.26 l) and voluntary water intake during recovery (0.416±0.299 v 0.294±0.295 l) (p<0.05) were greater in HIIE. Serum osmolality (297±3 v 288±4mOsmol.kg-1), blood lactate (8.5±2.7 v 0.7±0.4mmol.l-1), serum sodium (146±1 v 143±1mmol.l-1) and vasopressin (9.91±3.36 v 4.43±0.86pg.ml-1) concentrations were higher after HIIE (p<0.05) and thirst (84±7 v 60±21) and mouth dryness (87±7 v 64±23) also tended to be higher (p=0.060). Greater voluntary water intake after HIIE was mainly caused by increased sweat loss and the consequences of increased serum osmolality mainly resulting from higher blood lactate concentrations.