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Jump exercise during remobilization restores integrity of the trabecular architecture after tail suspension in young rats

¹Department of Health and Sports Sciences, Kawasaki University of Medical Welfare, Kurashiki; ²Department of Nuclear Medicine, Kawasaki Medical School, Kurashiki; ³Graduate School of Sport Sciences, Waseda University, Tokorozawa, Japan

Submitted 21 September 2007 ; accepted in final form 15 April 2008

Three-dimensional trabecular architecture was investigated in the femora of tail-suspended young growing rats, and the effects of jump exercise during remobilization were examined. Five-week-old male Wistar rats (n = 35) were randomly assigned to five body weight-matched groups: tail-suspended group (SUS; n = 7); sedentary control group for SUS (S_CON; n = 7); spontaneous recovery group after tail suspension (S+R_CON, n = 7); jump exercise group after tail suspension (S+R_JUM; n = 7); and age-matched control group for S+R_CON and S+R_JUM without tail suspension and exercise (S_CON+R_CON; n = 7). Rats in SUS and S_CON were killed immediately after tail suspension for 14 days. The jump exercise protocol consisted of 10 jumps/day, 5 days/wk, and jump height was 40 cm. Bone mineral density (BMD) of the femur and three-dimensional trabecular bone architecture at the distal femoral metaphysis were measured. Tail suspension induced a 13.6% decrease in total femoral BMD (P < 0.001) and marked deterioration of trabecular architecture. After 5 wk of free remobilization, femoral BMD, calf muscle weight, and body weight returned to age-matched control levels, but trabeculae remained thinner and less connected. On the other hand, S+R_JUM rats showed significant increases in trabecular thickness, number, and connectivity compared with S+R_CON rats (62.8, 31.6, and 24.7%, respectively; P < 0.05), and these parameters of trabecular architecture returned to the levels of S_CON+R_CON. These results indicate that suspension-induced trabecular deterioration persists after remobilization, but jump exercise during remobilization can restore the integrity of trabecular architecture and bone mass in the femur in young growing rats.

jump exercise; tail suspension (unloading); remobilization; trabecular architecture; microcomputed tomography