BLOOD SERUM BIOCHEMICAL CHANGES IN PHYSICALLY CONDITIONED AND UNCONDITIONED SUBJECTS DURING BED REST AND CHRONIC HYPERHYDRATION

SUMMARY 1. It has been suggested that prolonged exposure to a rigorous bed rest regimen (hypokinesia) may induce greater serum carbohydrate and electrolyte changes in physically conditioned than unconditional subjects and that chronic hyperhydration may normalize or attenuate the development of these biochemical alterations in physically conditioned subjects. 2. Serum carbohydrate and electrolyte changes were determined in 18 physically healthy male volunteers aged 19–24 years during 30 days of a rigorous bed rest regimen. The subjects were divided into three equal groups. The first g oup consisted of six unconditioned subjects with V̇o2 max of 44 mL/kg bodyweight/min, the second group consisted of six conditioned subjects with V̇o2 max of 69 mL/ kg bodyweight/ min and the third group consisted of six conditioned subjects with V̇o2 max of 69 mL/kg body weight/min who consumed daily an additional amount of 26 mL water/kg bodyweight and 0.10 mg sodium chloride/kg bodyweight. 3. For the simulation of the hypokinetic effect all volunteers were kept under a rigorous bed rest regimen for 30 days. During the pre hypokinetic period of 15 days and during the bed rest period of 30 days the concentrations of cortsol, aldosterone, testosterone, tri‐idothyronine (T3), thyroxine (total; T4), glucose, potassium, sodium and chloride were determined in blood serum of volunteers. 4. During the bed rest period of 30 days serum carbohydrate and electrolyte changes were more pronounced in physically conditioned than unconditioned hypokinetic subjects. In physically conditioned hyperhydrated subjects serum carbohydrate and electrolyte changes were less pronounced than in physically conditioned and unconditioned hypokinetic subjects. 5. It was concluded that exposure to a rigorous bed rest regimen over a prolonged period of time induced significantly more changes in serum carbohydrate and electrolyte concentrations in physically conditioned than in unconditioned subjects and that chronic hyperhydration may be used to normalize or stabilize all serum biochemical changes in physically conditioned subjects during prolonged exposure to a rigorous bed rest regimen.