Hydration status and fluid balance of elite European youth soccer players during consecutive training sessions

The objective of the study was to investigate the hydration status and fluid balance of elite European youth soccer players during three consecutive training sessions. Fourteen males (age 16.9 +/- 0.8 years, height 1.79 +/- 0.06 m, body mass (BM) 70.6 +/- 5.0 kg) had their hydration status assessed from first morning urine samples (baseline) and pre- and post-training using urine specific gravity (USG) measures, and their fluid balance calculated from pre- to post-training BM change, corrected for fluid intake and urine output. Most participants were hypohydrated upon waking (USG >1.020; 77% on days 1 and 3, and 62% on day 2). There was no significant difference between first morning and pre-training USG (p = 0.11) and no influence of training session (p = 0.34) or time (pre- vs. post-training; p = 0.16) on USG. Significant BM loss occurred in sessions 1-3 (0.69 +/- 0.22, 0.42 +/- 0.25, and 0.38 +/- 0.30 kg respectively, p <0.05). Mean fluid intake in sessions 1-3 was 425 +/- 185, 355 +/- 161, and 247 +/- 157 ml, respectively (p <0.05). Participants replaced on average 71.3 +/- 64.1% (range 0-363.6%) of fluid losses across the three sessions. Body mass loss, fluid intake, and USG measures showed large inter-individual variation. Elite young European soccer players likely wake and present for training hypohydrated, when a USG threshold of 1.020 is applied. When training in a cool environment with ad libitum access to fluid, replacing similar to 71% of sweat losses results in minimal hypohydration (= 2% BM) dehydration, as advised by current fluid intake guidelines. Current fluid intake guidelines appear applicable for elite European youth soccer players training in a cool environment.