Evaluation of body fluids changes in sport practice and effects of dehydration during exercise

This thesis aimed: 1. to examine the accuracy of classic and specific bioimpedance vector analysis (BIVA) in body composition assessment of athletes, focusing the analysis on absolute values of body mass [fat mass (FM), fat-free mass (FFM), total body water (TBW), extracellular water (ECW), intracellular water (ICW)] and on values independent from body dimensions (%FM, ICW/ECW); 2. to explore the suitability of BIVA in evaluation long-term body fluid changes, over a competitive season in athletes; 3. to determine the time course of bioimpedance values after a period of controlled exercise and when a cold shower with a standardized duration and water temperature was applied; 4. to determine the effects of dehydration on neuromuscular functionality and time trial (TT) performance during a cycling exercise in athletes. Specific BIVA turns out to be more accurate for the analysis of %FM in athletes, while it does not correctly evaluate TBW, for which classic BIVA appears to be a suitable approach. The vector changes measured with BIVA convincingly mirror fluids loss or gain over a season. Additionally, peripheral vectors lying on the left or right side of the minor axis of the BIVA tolerance ellipses indicate more or less ICW/ECW, respectively. BIVA might be a valuable tool in identifying dehydration and fluid shifts after physical exercise. A 10-minute cold shower enables the stabilization of bioimpedance analysis measurements within 20 minutes after 30 minutes running exercise, which might facilitate the assessment of hydration change after exercise. Otherwise, without shower the time until reaching stable bioimpedance values is prolonged to 40 min. After exercise induced dehydration, the bioimpedance vector significantly lengthens along the major axis of the tolerance ellipse, in conformity with body weight loss. Neuromuscular function, assessed by surface electromyography on the thigh muscles, shows a lower muscle activation in TT performance in dehydration conditions.