Jump exercise during hindlimb unloading protect against the deterioration of trabecular bone microarchitecture in growing young rats

Abstract

Three-dimensional femoral trabecular architecture was investigated in tail-suspended young growing rats and the effects of jump exercise during the period of tail-suspension were also examined. Eight-week-old male Wistar rats (n = 24) were randomly assigned to three body weight-matched groups: a tail suspended group (SUS, n = 8); a sedentary control group (CON, n = 8) and rats primed with jump exercise during the period of tail suspension (JUM, n = 8). The jump exercise protocol consisted of 30 jumps/day, five days/week with a 40 cm jump height. After 3 weeks of jump exercise, bone mineral density (BMD) of the entire right femur was measured using dual energy X-ray absorptiometry. Three-dimensional trabecular bone architecture at the distal femoral metaphysis was evaluated using microcomputed tomography (micro-CT). Tail suspension caused a decrease in femoral BMD (−5%, p < 0.001) and trabecular bone architectural deterioration. Deterioration in the trabecular network during hindlimb unloading was mostly attributed to the reduction of trabecular number (−32%, p < 0.001) in the distal femoral metaphysis. Jump exercise during the tail suspension period increased trabecular thickness (14%, p < 0.001) and the reduction of trabecular number was suppressed. The present data indicate that jump exercise applied during hindlimb unloading could be able to inhibit bone loss and trabecular bone architectural deterioration caused by tail suspension.

The Effect of Prior Exercise on Bone Morphological Microstructure after Immobilization in Mice

“…In agreement with this report, Scofield and Hecht showed that adolescents and adults who participated in non-weightbearing sports (e.g., swimming) often had lower bone mineral density than athletes participating in weight-bearing sports (e.g., running) [18]. In contrast, previous studies have shown an osteogenic effect of muscle contraction in the absence of weight-bearing conditions in rats, such as electrical stimulation while their tails are suspended, or when the rats were under paraplegic conditions [10,13,14,30,31]. In our study muscle contraction during swimming activity significantly improved bone quality, suggesting that bone tissue responds to mechanical loading by stimulating bone formation where strain is higher [22].…”

“…As a result, exercise, antiresorptive drugs, and other techniques, such as electrical muscle stimulation, have been proposed as therapies to improve or prevent bone deterioration [10][11][12][13][14][15][16][17]. Rubin et al studied the effects of periods of unloading, interrupted either by regular weight bearing or vibration therapy, on the bone quality of rats.…”

“…The authors found that vibration therapy, but not weight bearing, attenuated bone loss secondary to disuse [14]. Ju et al observed that jump exercise intercalated with skeletal unloading showed a positive effect on the bone suppression of tail suspension-induced osteopenia in rats, by completely preserving bone deterioration due to unloading [10]. However, which type or regimen of muscular exercise would contribute more to restoring or preventing poor bone quality remains unclear, based on the divergent reports in the literature [18][19][20].…”

High-Impact Drop Exercise Alters Mechanical Properties in Osteopenic Bone

“…The skeleton is constantly subjected to mechanical loading because of gravitational force and muscle contraction, which stimulate bone remodeling through mechanotransduction. Osteocytes are able to detect the mechanical signals and modulate bone formation and resorption by signaling osteoblasts and osteoclasts, respectively 9 . The results of this study showed that dropping 20 times per session on a daily basis increased bone material properties in estrogen-deficient rats and control rats in both prevention and treatment groups.…”

“…Jumping appears to promote superior bone formation compared with low impact aerobic exercises [7][8][9][10][11][12] . The mechanical stress caused by high impact exercise is crucial for the structural and functional integrity of the skeletal system, since it increases BMD and other properties of bones 6 .…”