Thirst responses following high intensity intermittent exercise when access to ad libitum water intake was permitted, not permitted or delayed

An increase in subjective feelings of thirst and ad libitum drinking caused by an increase in serum osmolality have been observed following high intensity intermittent exercise (HIIE) compared to continuous exercise. The increase in serum osmolality is closely linked to the rise in blood lactate and serum sodium concentrations. However, during an ensuing recovery period after HIIE when serum osmolality will decrease, the resultant effect on sensations of thirst and subsequent water intake is unclear. Therefore the aim of the study was to assess the sensations of thirst and subsequent effect on ad libitum water consumption when water intake was immediately allowed, delayed or prevented following a period of HIIE.Twelve males (26 ± 4 years, 80.1 ± 9.3 kg, 1.81 ± 0.05 m, V̇O2peak 60.1 ± 8.9 ml.kg(-1).min(-1)) participated in three randomised trials undertaken 7-14 days apart. Participants rested for 30 min then completed a 60 min HIIE exercise period (20 x 1 min at 100% V̇O2peak with 2 min rest) followed by 60 min of recovery, during which ad libitum water intake was provided immediately (W), delayed until the final 30 min (W30) or not permitted (NW). Body mass was measured at the start and end of the trial. Blood lactate and serum sodium concentrations serum osmolality and sensation of thirst were measured at baseline, immediately post-exercise and during the recovery.Body mass loss was different between all trials (W: 0.25 ± 0.45, W30: 0.49 ± 0.37, NW: 1.29 ± 0.37%; p<0.05). Sensations of thirst peaked post-exercise and decreased in W and W30 following water ingestion (p<0.05). Total voluntary water intake was greater in W trial (0.846 ± 0.417 v 0.630 ± 0.277 l; p<0.05) but was similar during the first 30 min period of allowed drinking (0.618 ± 0.297 vs. 0.630 ± 0.277 l; p>0.05). Serum osmolality (299 ± 6 v 298 ± 5 vs. 298 ± 3 mOsmol.kg(-1)), blood lactate (7.1 ± 1.1 vs. 7.2 ± 1.1 v 7.1 ± 1.2 mmol.l(-1)) and serum sodium concentrations (142 ± 2 vs. 145 ± 2 v 145 ± 2 mmol.l(-1)) peaked post-exercise (W vs. W30 vs. NW; p<0.05) but were not different between trials (p>0.05).Sensations of thirst were increased following HIIE and remained until satiated by water intake. This was despite the likely primary stimulus, serum osmolality, decreasing during the recovery period following a post-exercise peak. A combined effect of reduction in blood lactate and serum sodium concentrations, restoration of plasma volume and water intake contributed to the similar decrease in serum osmolality observed throughout the trials.