URINARY AND PLASMA CALCIUM CHANGES IN ENDURANCE-TRAINED VOLUNTEERS DURING EXPOSURE TO ACUTE AND RIGOROUS BED REST CONDITIONS

The purpose of the present study was to evaluate the effect of acute ( abrupt restriction of muscular activity) and rigorous bed-rest conditi ons on urinary and plasma calcium changes in endurance trained volunte ers. The studies were performed on 30 long distance runners ages 23-25 who had a peak oxygen uptake of 66.0 mL/min/kg and had run 14.0 km/d on the average prior to their participation in the study. The voluntee rs were divided into three groups: The volunteers in the first group w ere under normal ambulatory conditions (control subjects), the second group was subjected to an acute bed-rest regime (acute bedrested subje cts), and the third group was submitted to a rigorous bed-rest regime (rigorous bedrested subjects). The second and third groups of voluntee rs were kept under a rigorous bed rest regime for 7 d. During the pre- bedrest period and during the actual bed-rest periods (acute and rigor ous bed-rest periods), urinary excretion of calcium and plasma calcium and parathyroid hormone (PTH) concentrations were determined. During the 1st d of acute and rigorous bed-rest periods, urinary excretion an d plasma concentration of calcium increased significantly (P less than or equal to 0.05), while plasma parathyroid hormone content decreased significantly (P less than or equal to 0.05). On the 3rd d of the exp erimental period, urinary excretion and plasma calcium concentration d ecreased somewhat, during the 7th d, calcium in urine and plasma incre ased further, while parathyroid hormone content in plasma increased so mewhat on the 3rd d and decreased again on the 7th d of the experiment al period. The changes were more pronounced in the volunteers who were subjected to acute bed-rest conditions than in the volunteers who wer e submitted to rigorous bed-rest conditions. It was concluded that exp osure to acute bed-rest conditions induces significantly greater urina ry and serum calcium changes than rigorous bed-rest conditions in endu rance trained volunteers.