Phosphate-loading tests influences on endurance-trained volunteers during restriction of muscular activity and chronic hyperhydration

The purpose of this investigation was to determine whether negative phosphate balance, which is developed during hypokinesia (a decreased number of walking steps/d) could be reversed with daily supplementation with phosphate, fluid, and salt (FSS). The studies on hypokinesia (HK) were performed for 364 d on 30 endurance-trained male volunteers in the age range of 23–26 yr, with an average maximum oxygen uptake, MOU, of 65 mL/kg min. All subjects were divided into three equal groups: Ten volunteers were placed on a continuous regime of exercise of 14.4 kmJd at 10,000 steps/d and served as controls. Ten volunteers were subject to continuous HK without FSS and were considered as the hypokinetic subjects (HS). The remaining subjects were under continuous HK and FSS and were considered as the hypokinetic, hyperhydrated subjects (HHS). The three groups were on a diet that averaged 2620 cal/d and contained 1.7 g calcium, 1.6 g phosphate, and 5.6 g sodium chloride. For simulation of the hypokinetic effect, the HS and HHS groups were kept continuously under 2.9 km/d (3000 walking steps/d) for the duration of the study. Prior to exposure to HK, all volunteers were on the same exercise regime as the controls. During a 60-d pre-HK period and during the remainder of the study, phosphate-loading tests, urinary and plasma phosphate concentrations were performed in all subjects. In the HHS group, plasma phosphate concentration and urinary excretion of phosphate were decreased, while in the HS group these values increased after phosphate loading. Based on our results, we concluded that chronic hyperhydration and phosphate supplementation may be used to minimize phosphate losses in endurance-trained volunteers during prolonged restriction of muscular activity.