Abstract
We investigated the effectiveness of resistance exercise (RE) against musculoskeletal dysfunction after 3-week of hindlimb unloading (HU). Female F344 rats (16-week old) were divided at random into the HU (n=6), HU with RE (n=7), and age-matched control (n=6) groups. RE was performed continuously for 30 minutes with an additional load of 50% body mass attached to rat's tail, once a day, 6 days a week. The isometric contractile function and myosin heavy chain (MHC) isoform composition of the soleus were measured. Bone mineral content (BMC) and bone mineral density (BMD) were determined in the whole and in five equally divided regions along the longitudinal axis of the femur from proximal (R1) to distal (R5) regions. The maximum force and force normalized by soleus mass decreased due to HU. Also, the soleus were characterized by the faster contraction and relaxation, and the higher type II isoform composition of MHC after HU. RE ameliorated these changes. HU resulted in significant losses of BMC and BMD of the whole femur. Significant decreases were observed in R2, R4, and R5 for BMC and in R1, R4, and R5 for BMD due to HS. RE slightly prevented losses of BMC and BMD in the whole femur. Interestingly, RE prevented the decreases of BMC and BMD in R5. These results indicated that RE is an effective countermeasure for preventing musculoskeletal dysfunction and that bone responses to HU and/or RE were site-specific. [J Physiol Sci. 2007;57 Suppl:S188]
