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. Thu.s, the aim was to assess voluntary water intake following HIIE. Ten healthy males (22 ± 2 y, 75.6 ± 6.9 kg, VO2(peak) 57.3 ± 11.4 m · kg(-1) · min(-1); mean ± SD) completed two trials (7-14 d apart). Subjects sat for 30 min then completed an exercise period involving 2 min of rest followed by 1 min at 100% VO2(peak repeated for 60 min (HIIE) or 60 min continuously at 33% VO2(peak) (LO). Subjects then sat for 60 min 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, postexercise and after 5, 15, 30, and 60 min of recovery. Vasopressin concentration was measured at baseline, postexercise, 5 min, and 30 min. Body mass loss over the whole trial was similar (HIIE: 0.77 ± 0.50; LO: 0.85 ± 0.55%; p = .124). Sweat lost during exercise (0.78 ± 0.22 vs. 0.66 ± 0.26 L) and voluntary water intake during recovery (0.416 ± 0.299 vs. 0.294 ± 0.295 L; p < .05) were greater in HIIE. Serum osmolality (297 ± 3 vs. 288 ± 4 mOsmol · kg(-1)), blood lactate (8.5 ± 2.7 vs. 0.7 ± 0.4 mmol · L(-1)), serum sodium (146 ± 1 vs. 143 ± 1 mmol · L(-1)) and vasopressin (9.91 ± 3.36 vs. 4.43 ± 0.86 pg · ml(-1)) concentrations were higher after HIIE (p < .05) and thirst (84 ± 7 vs. 60 ± 21) and mouth dryness (87 ± 7 vs. 64 ± 23) also tended to be higher (p = .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.