This study investigated how different treadmill running periods effected bone mechanical strength in ovariectomized mice. Eighty female ICR mice aged 12-weeks-old were used. All mice were divided into 8 groups (n=10) randomly, and had either a sham-operation (n=10) or an ovariectomy (n=70). The SHAM group and one OVX group (NR) were used as non-running control groups, with the remainder comprising the treadmill running groups : the LA (8 m/min), MA (16 m/min), and HA (24 m/min) groups which ran for 12 weeks, and the LB (8 m/min), MB (16 m/min), HB (24 m/min) groups which ran for 6 weeks for 25 min on 5 days/week. After this experiment, maximum loads for the femur and tibia were measured by three-pointed bending test, and the bone mechanical strength of the bones was calculated. Also, the dry bone weight and ash content of the bones were measured. Maximum femur and tibia load and bone mechanical strength were affected by running speed and term significantly. Maximum load and bone mechanical strength of tibia were shown as an interaction. Bone mechanical strength in all running groups was higher than that in the NR group, significantly. This study suggested that treadmill running prevented a reduction of bone mechanical strength, and that treadmill running was most effective in the LA and MA groups (running at low and medium speed and for a long period).

Effects of running speed and duration on a treadmill on bone properties were investigated in ovariectomized (OVX) mice. Sixty female ICR mice, twelve-weeks-old, were used in this study. They were divided into six groups of 10 mice each : either the SHAM, OVX, OVX+running groups (AS, AL, BS, BL), randomly. Running groups ran on the treadmill at 8 (A) or 16 (B) m/min, for 25 (S) or 50 (L) min, 5 days/week, for 10 weeks, respectively. After this, both femur and tibia bones were excised from the hind limb, and removed off surrounding tissues. Thereafter, bone mechanical strength (3 point bending test), dry bone weight and also ash content of the bones were determined. Bone mechanical strength and ash content of the femur and tibia in AL, BS, and BL mice were significantly higher than those in OVX mice. Running speed had effects on the bone mechanical strength and ash content of both bones significantly. Group BL showed the maximum values in bone properties among the running groups. This study suggested that a combination of running speed and duration could affect bone properties more significantly than the amount of exercise alone.

This study investigated the effects of electrical stimulus on bone properties in rats with sciatic denervation. Forty-eight Wistar rats aged 8 week-old were used and divided into 4 groups, randomly. One group was sham-operated (SHAM) as a control, and the sciatic nerves of the lateral hind limbs were cut in the remaining 3 groups (DN). Two groups of DN rats received electrical stimulus at both hind limbs to induce planter flexion for 15 min, 2 sets/day, 5 days/week, at 15 or 60 Hz. The rats in each group were sacrificed at 1, 2, 3 and 4 weeks after the operation. All tibias were measured by three-pointed bending test, and bone mechanical strength was calculated. Also, the dry bone weight and ash content of the bones were measured. A reduction of all bone properties in DN was shown from a week after operation onwards and that in DN+15 Hz from two weeks after operation onwards. Bone properties in DN+60 Hz were decreased in order of maximum load, ash content, mechanical strength, and dry bone weight from two weeks after operation onwards. These results suggest that electrical stimulus can delay the progression of bone atrophy, and that high frequency stimulation (60 Hz) is more effective than low frequency stimulation (15 Hz) in this regard.