Effects of immobilization, three forms of remobilization, and subsequent deconditioning on bone mineral content and density in rat femora

Disuse is associated with bone loss, which may not be recoverable. It is not known whether intensified remobilization is beneficial in restoring disuse‐related bone loss nor if any such benefit would depend upon continuing mobilization for its maintenance. After an immobilization period of 3 weeks, the effects of free remobilization (11 weeks), and low‐ and high‐intensity treadmill running (11 weeks) with and without subsequent deconditioning (18 weeks) on the bone mineral content (BMC) and density (BMD) of the hindlimb femora of Sprague‐Dawley rats (n = 98) were studied using a dual‐energy X‐ray absorptiometric (DXA) scanner. Our hypothesis was that intensified remobilization is beneficial in restoring the BMC and BMD from disuse to normal while subsequent deconditioning is deleterious to these parameters. Immobilization for 3 weeks produced a significant BMC and BMD loss in the immobilized left femur (range −4.4 to −12.8%; p < 0.05‐0.001). In the groups with free remobilization (free cage activity), the body weight‐adjusted BMCs and BMDs always remained below those in the controls (range −2.3 to −12.1%; p values ranging from NS to