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Abstract  The frequency per week or day of high-impact, low-repetition jump exercise for osteogenic response was assessed by two experiments. In the first experiment, 48 11-week-old rats were randomly divided into five groups: a sedentary control (W0: n = 8), one exercise session per week (W1: n = 10), three exercise sessions per week (W3: n = 10), five exercise sessions per week (W5: n = 10), and seven exercise sessions per week (W7: n = 10). In the second experiment, 30 11-week-old rats were randomly divided into three groups: a sedentary control (D0: n = 10), one exercise session per day (D1: n = 10), and two exercise sessions per day (D2: n = 10). One exercise session consisted of 10 continuous jumps. After 8 weeks of the exercise period, the jump exercise increased the fat-free dry weight of the tibia in the W1 (7.5%, n.s.), W3 (12.6%, P P P P P [ABSTRACT FROM AUTHOR]

Abstract  Jump exercise in rats creates high-impact loading on lower limbs and results in the promotion of osteogenesis. Although we clarifi ed that a few loadings per day could increase bone mass and strength within 8 weeks, we did not observe an osteogenic response at the onset of the training period. The purpose of this study was to clarify whether the bone formation rate measured by the double-label immunofluorescence method increases with a few loadings for a short period. Forty female Wistar rats, 10 weeks old, were divided into a control group and three exercise groups: the 10 jumps/day (10 J) group, 40 jumps/day (40 J) group, and 100 jumps/day (100 J) group. The exercise groups were trained on days 1, 3, and 5, the fluorescent labels were injected on days 5 and 12, and the experiment ended on day 16. The bone formation rates were greater in all exercise groups compared with the control group and were significantly greater in the 40 J and 100 J groups than in the 10 J group. These data show that only 10 repetitions/day loading promotes the osteogenic response within a short period from the onset of the training. [ABSTRACT FROM AUTHOR]