title: Body composition and hydration status changes in male and female open-water swimmers during an ultra-endurance event.
abstract: Body mass changes during ultra-endurance performances have been described for running, cycling and for swimming in a heated pool. The present field study of 20 male and 11 female open-water swimmers investigated the changes in body composition and hydration status during an ultra-endurance event. Body mass, both estimated fat mass and skeletal muscle mass, haematocrit, plasma sodium concentration ([Na+]) and urine specific gravity were determined. Energy intake, energy expenditure and fluid intake were estimated. Males experienced significant reductions in body mass (-0.5 %) and skeletal muscle mass (-1.1 %) (P < 0.05) during the race compared to females who showed no significant changes with regard to these variables (P > 0.05). Changes in percent body fat, fat mass, and fat-free mass were heterogeneous and did not reach statistical significance (P > 0.05) between gender groups. Fluid intake relative to plasma volume was higher in females than in males during the ultra-endurance event. Compared to males, females' average increase in haematocrit was 3.3 percentage points (pp) higher, urine specific gravity decrease 0.1 pp smaller, and plasma [Na+] 1.3 pp higher. The observed patterns of fluid intake, changes in plasma volume, urine specific gravity, and plasma [Na+] suggest that, particularly in females, a combination of fluid shift from blood vessels to interstitial tissue, facilitated by skeletal muscle damage, as well as exercise-associated hyponatremia had occurred. To summarise, changes in body composition and hydration status are different in male compared to female open-water ultra-endurance swimmers.
authors.affiliation: Institute of General Practice and for Health Services Research, University of Zurich, Zurich, Switzerland.
authors.forename: Tim
authors.initials: T
authors.lastname: Weitkunat
authors.forename: Beat
authors.initials: B
authors.lastname: Knechtle
authors.forename: Patrizia
authors.initials: P
authors.lastname: Knechtle
authors.forename: Christoph Alexander
authors.initials: CA
authors.lastname: Rüst
authors.forename: Thomas
authors.initials: T
authors.lastname: Rosemann
mesh_terms: D000273:Adipose Tissue / Q000502:physiology; D000328:Adult; D056352:Athletes; D001823:Body Composition / Q000502:physiology*; D015992:Body Mass Index; D004326:Drinking / Q000502:physiology; D002149:Energy Intake / Q000502:physiology; D004734:Energy Metabolism / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology*; D010953:Plasma Volume / Q000502:physiology; D012737:Sex Factors; D012964:Sodium / Q000097:blood / Q000494:pharmacology; D013550:Swimming / Q000502:physiology*; D014882:Water-Electrolyte Balance / Q000502:physiology*
chemical_list: D012964:Sodium