Ad-libitum fluid intake was insufficient to achieve euhydration 20 h after intermittent running in male team sports athletes

This study documented 20 h rehydration from intermittent running while concealing the primary outcome of rehydration from subjects. Twenty-eight male team sports athletes (age 25 +/- 3 y; predicted VO2max 54 +/- 3 mL kg-1 min-1) were pair-matched to exercise (EX) or rest (REST) groups. To determine hydration status, body mass, urine and blood samples were collected at 08:00, pre-intervention (09:30), post-intervention (12:00), 3 h post-intervention and 08:00 the following morning (20 h). The intervention was 110 min intermittent running (EX) or seated rest (REST), with ad-libitum fluid provided in both. Subjects completed a weighed diet record and collected all urine for the 24 h. Changes typical of hypohydration were apparent in EX following the intervention period (body mass: EX -2.0 +/- 0.5%; REST -0.2 +/- 0.3%; serum osmolality: EX 293 +/- 4 mOsm center dot kgH2O- 1; REST 287 +/- 6 mOsm center dot kgH2O- 1; P <= 0.022). Fluid intake during the intervention period (EX 704 +/- 286 mL, REST 343 +/- 230 mL) and fluid intake within the first 3 h post-intervention (EX 1081 +/- 460 mL, REST 662 +/- 230 mL) were greater (P <= 0.004), and 24 h urine volume lower (EX 1697 +/- 824 mL, REST 2370 +/- 842 mL; P = 0.039) in EX. Compared to baseline, body mass remained lower (-0.6 +/- 0.5%; P = 0.030) and urine osmolality elevated (20 h: 844 +/- 197 mOsm center dot kgH2O- 1, 08:00: 698 +/- 200 mOsm center dot kgH2O- 1; P = 0.004) at 20 h in EX. When games players drank fluid ad-libitum during exercise and post-exercise in free-living conditions, a small degree of hypohydration remained 20 h post-exercise.

Automated summary

This study examined the rehydration process after intermittent running and found that a small degree of hypohydration remained even when subjects drank fluids ad-libitum during and after exercise. The results suggest that athletes may still experience dehydration to some extent despite fluid intake in free-living conditions.