Examining current hydration controversies in athletics

The relationship between hydration and thermoregulation is not as clear in the field setting compared to findings from decades of laboratory studies. The purposes of these investigations were (1) to determine the effects of dehydration on physiological function and running speed when relative intensity was controlled during a 12-km submaximal run, and (2) to determine the effects of two hydration protocols on core body temperature and trail running performance during a 20-km trail race. Fourteen (7 female; 7 male) competitive runners (age=29.8±10.4 y, height=172.9±7.4 cm, body mass=66.7±11.8 kg, 14.31±6.6%BF) completed two 12-km runs in either a hydrated (HY) or dehydrated (DHY) condition. BM losses were significantly greater for DHY pre-trial (−1.65±1.34%) than HY (−0.03±1.28%; p\u3c.001). DHY condition had significantly higher TGI post-run (DHY: 39.09±0.45°C, HY: 38.71±0.45°C; p=.030), 10-min post (DHY: 38.85±0.48°C, HY: 38.46±0.46°C; p=.009), and 30-min post (DHY: 38.18±0.41°C, HY: 37.60±0.25°C; p=.000). DHY resulted in significantly slower run times after Lap 2 and Lap 3 (p=.025), with DHY completing the 12-km run 99 seconds slower than HY (p=0.027). In the second study, thirteen (8 males, 5 females) experienced runners (age: 39±14y; height: 175±9cm; mass: 67.5±11.1kg; body fat: 13.4±4.6%) completed two 20-km trail races with 2 protocols: ad libitum (AL) drinking and individualized rehydration (IR). HR and TGI responses and race performance were similar between conditions. AL resulted in −2.6% BM loss while IR resulted in −1.3% BM loss (p\u3c0.05). Subjects drank 32±13% of their fluid needs in AL and 66±13% of their fluid needs in IR (p=0.000). Percent PV Δ from pre- to post-race were significantly higher in AL (−4.9±5.5%) compared to IR (−1.0±4.6%; p=0.013). Pre- to post-race Δ was greater in AL compared to IR for U osm, Na+, and Cl− (p=0.000). These findings suggest that when control is utilized in the field, the relationship between hydration status and thermoregulation is evident. This also illustrates that even experienced athletes may not adequately replace fluids when given the ad libitum option.