Relationship Between Fitness Levels And Body Composition On Hydration During An Indoor 5 km Treadmill Run

Maintaining proper hydration status is a vital part of maximizing athletic performance. Previous research has demonstrated that trained individuals have a greater sweat rate (SR) than non-trained individuals, however, SR also has high inter-individual variability due to multiple factors. It remains unclear how factors such as fitness level or body composition in similarly trained individuals are associated with hydration status during running. PURPOSE: Determine the relationship between fitness levels and body composition on measures of hydration status and SR during an indoor 5 km run. METHODS: 16 participants who engaged in running activities 3-4 days/week, each with a self-estimated half-marathon race pace of 7:30 min/mi (8 M/8F; age: 38 ± 13 yrs; BMI: 21.8 ± 2.9 kg/m2) were imaged by dual energy x-ray absorptiometry to assess percent total body fat (%TBF) and performed a treadmill graded maximal exercise test to measure functional capacity. The test started at 10 km/hr and increased 1 km/hr every 3 min until volitional fatigue. Maximal (VO2max) and submaximal (running economy [RE]; VO2 at 13 km/hr) oxygen consumption was used for analysis. On a separate day (25 ± 6 days after VO2max visit), participants performed an indoor (temperature: 22.9 ± 1.1oC; humidity: 46.5 ± 2.8%) treadmill 5 km run at a self-selected training pace (RPE: 11.1 ± 1.8). Nude body mass and urine samples were collected pre and post 5 km run. SR (mL/hr) was calculated from body mass changes, and percent change in urine osmolality (ΔUosmo) and specific gravity (ΔUSG) were used to assess hydration status. Pearson r correlations assessed the independent relationships between VO2max, RE, %TBF and SR, ΔUosmo and ΔUSG. RESULTS: VO2max (52.8 ± 3.4 mL/kg/min), RE (46.5 ± 3.2 mL/kg/min), and %TBF (20.8 ± 5.6%) were not significantly correlated with SR (1094.8 ± 490.1 mL/hr), ΔUosmo (-8.5 ± 54.3%) or ΔUSG (-0.2 ± .4%) (r2-range: .13-.23; p > .05). CONCLUSION: Fitness levels and body composition values were not significantly associated with SR or hydration status during an indoor 5 km run. Future research is needed to determine whether these relationships are affected during more extreme conditions, such as longer run, or greater temperature stress. This study received funding from Samsung Electronics Co., Ltd. This study received funding from Samsung Electronics Co., Ltd.