High-impact exercise frequency per week or day for osteogenic response in rats.

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 < 0.01), W5 (12.0%, P < 0.01), and W7 (19.8%, P < 0.001) groups compared with the W0 group. The jump exercise also increased the fat-free dry weight in the D1 (12.0%, P < 0.001) and D2 (13.0%, P < 0.001) groups compared with the D0 group. These increases were accompanied by increased bone strength and cortical area at the mid-shaft. The results in the present study suggest that for bone gain, it is not always necessary to do high-impact exercise every day, although exercising every day does have the greatest effect. The results in this study also suggest that there is little additional benefit if bones are loaded by two separate exercise sessions daily.