Intracellular hyperhydration induced by a 7-day endurance race

Abstract

To test the hypothesis that a chronic expansion of extracellular water (ECW), usually observed during prolonged endurance exercise, is associated with an increase in intracellular water space (ICW), total body water (TBW) and ECW were estimated before (within a week, day C-7) and after (on the 1st day of recovery, R+1) a competition lasting 7 consecutive days in nine healthy sportsmen. The competition involved running, cycling and cross-country skiing over 620 km. Between days C-7 and R+1, the following increases occurred – mean TBW by 4.2 (SEM 1.1) l (i.e. +10%, P = 0.01, bioelectrical impedance analysis, BIA, at 100 kHz) and by 4.1 (SEM 0.7) l (P = 0.01, dilution of ¹⁸O); mean ECW by 2.2 (SEM 0.5) l (i.e. +14%, P = 0.01, BIA at 5kHz), and mean plasma volume (PV) by 0.7 (SEM 0.1) l (i.e. +22%, Evans blue dye dilution, P = 0.008). Consequently, mean ICW had been expanded by 2.1 (SEM 0.6) l (i.e. +8%, P = 0.01). The intensity of daily exercise evaluated from recordings of heart rate varied between 49.0% to 57.8% of maximal oxygen consumption V˙O_2max. Water retention was highly correlated with relative exercise intensity V˙O_2max (ICW, r=0.86; ECW, r=0.93; TBW, r=0.94). Total mean plasma content of sodium increased by 104 (SEM 17) mmol (P = 0.008) while albumin and total protein contents were unchanged. We concluded that prolonged and repeated exercise induced a chronic hyperhydration at both extracellular and intracellular levels, which was related to exercise intensity. Sodium retention was the major factor in the increase of PV.