After an immobilization period of 3 weeks, the effects of free remobilization (8 weeks) as well as low‐ and high‐intensity treadmill running on the bone mineral content (BMC) and density (BMD) of the hindlimbs of Sprague‐Dawley rats (n = 70) were studied using a dual‐energy x‐ray absorptiometric scanner. In the low‐intensity running program, the rats were allowed to move freely in the cage for 1 week, after which they started to run on a treadmill twice a day for 7 weeks. The speed of the treadmill was 20 cm/s, with an uphill inclination of 10°. The running time was gradually increased from 20 minutes per session to 45 minutes per session. In the high‐intensity group, the program was similar, with the exception that the speed of the treadmill was 30 cm/s, with an uphill inclination of 30°. Immobilization for 3 weeks produced a significant BMC and BMD loss in the immobilized left femur and tibia (mean loss 9.6%, p < 0.001) but did not affect the right free limbs. Both low‐ and high‐intensity running restored mineral content in the immobilized limb; however, an average 5% difference (p < 0.05) in mineral content of the right and left limb bones persisted. In the running groups, the values for the immobilized left limbs were at the same level or exceeded (range 3.8–11.6%, p < 0.05–0.01) and those of the free right limbs exclusively exceeded (range 5.3–15.9%, p < 0.05–0.01) the corresponding values of the age‐matched control rats. In the group with free remobilization, the BMCs and BMDs always remained below those in the controls (range –3.2 to –12.6%, p values ranging from NS to p < 0.01). Thus, this study showed the need for greater than normal activity to restore the BMC and BMD from disuse to normal.
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism
- Orthopedics and Sports Medicine