PHYSICAL-FITNESS INFLUENCES WATER TURNOVER AND BODY-WATER CHANGES DURING TREKKING

Purpose: This study was performed to assess water turnover and changes of body water during a trekking tour at moderate altitude. Methods: F ifteen healthy normally trained adults participated in a 7-d backpack trek tour in the Swiss Alps (total walking distance: 120.5 km; cumulat ed altitude difference: 6990 m (uphill) and 7550 m downhill; lowest po int: 1285 m; highest point: 3317 m). Total body water and water turnov er were measured using deuterium dilution and elimination (oral load o f 0.33 g 99.8% D2O per kg body weight, overnight equilibration period, pre-and postdose saliva samples immediately before and after sleep, a nalysis of D2O concentrations in saliva using Fourier-transform infrar ed spectroscopy, CV < 1%). Physical training state was assessed after the tour using the lactate-exercise intensity relationship obtained by performing 50-W increments every 3 min on a cycle egometer. Results: Body water decreased from the evening of day 0 to the evening of day 4 (from 45.3 +/- 7.3 L to 43.4 +/- 7.6 L, P < 0.05), and did not signif icantly decrease (43.5 +/- 7.9 L) until the evening of day 5 (maximum of trekking exercise intensity). Mean daily water turnover was 5.7 +/- 1.8 L.d(-1) corresponding to 78.7 +/- 17.5 mL.kg(-1).d(-1). Body wate r changes and water turnover were significantly related to the exercis e intensity obtained at the lactate threshold as well as at the level of 4 mM lactate. Conclusions: This correlation may be in part explaine d by differing glycogen content of muscle tissue.