Prolonged bed rest may result in osteoporosis with hypercalciuria. In the present study the radial mineral content (RMC) and bone density of the second metatarsal bone were measured in elderly subjects in order to elucidate the relationship between the degree of physical activity and the amount of bone mass. The following results were obtained:
　(1) RMC in bedside group was significantly lower than that in outdoor group (p<0.05 and p<0.001 in the 8th and 9th decade males, p<0.01 in 9th decade females).
　(2) No significant difference was observed in bone density of the second metatarsal bone between the bedside group and the outdoor group of males. On the other hand three indices (GS max, GS min and ΣGS/D) showed lower values in the bedside group than outdoor group of female (p<0.05, respectively).
　(3) Although no significant difference in serum Ca, P and alkaline phosphatase levels was observed between the bedside group and the outdoor group, more increased urinary Ca excretion (Ca/creatinine) was found in the bedside group than the outdoor group (p<0.01).
　These findings indicate that bone loss with increased urinary Ca excretion is induced by the reduced physical activity, and that exercise is important to protect the bone loss.

DESCENTE SPORTS SCIENCE Vol.7/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE