EFFECT OF HIGH-IMPACT TRAINING AT DIFFERENT FREQUENCIES ON OSTEOGENIC RESPONSE IN RATS / 体力科学

ABSTRACT

Mechanical stress imposed by physical exercise is known to play an important role in increasing bone mass and preventing osteoporosis. As repetitional loadings may diminish mechano-sensitivity of bone cell, understanding shifts in mechano-sensitivity is important for making an effective training program for bones. The primary purpose of this study was to investigate bone responses when rats performed 400 repetitions of jump exercise in total using different training programs over 40 days. The secondary purpose was to clarify whether loading magnitude affects the results. This study comprised two experiments (EX1, EX2). In each experiment, 60 female Wistar rats (10-weeks-old) were divided into 1 sedentary group and 4 exercise groups. The 4 exercise groups were exercised with 10 jumps every day (10 jumps/day), 20 jumps every other day (20 jumps/2 days), 50 jumps every 5 days (50 jumps/5 days) or 100 jumps every 10 days (100 jumps/10 days). Jump height was set at 40 cm in EX1 and 30 cm in EX2. After 40 days, the 10 jumps/day, 20 jumps/2 days and 50 jumps/5 days groups in EX1 and EX2 showed significantly greater bone mass and strength compared to each sedentary group, although differences in training effects between these 3 groups were little. The 100 jumps/10 days group in EX1 also showed significantly greater bone mass and strength compared to the sedentary group, but the training effect was less. The 100 jumps/10 days group in EX2 did not show significantly greater bone mass and strength compared to the sedentary group. These results suggest that exercise everyday or every other day is not always necessary for bone development.