Regional adaptation of trabecular bone structure to jump training: effects of daily loading frequency on rats

High-impact loading, such as jump exercise, is effective to increase bone mass and strength. However, the effect of high-impact loading on regional bone adaptation has not been investigated in detail. This study investigated the differential effects of jump training on tibial and femoral morphology under different training conditions.

Nine-week-old male Wistar rats were randomly assigned to two training groups (n = 12 /group) and a control group (n = 8). The training groups included a group that performed five 10-jumps with two-hour intervals between bouts (J10 × 5) or that performed a 50-jump at once (J50 × 1). The jump training comprised 3 days/week for 8 weeks at a jump height of 40 cm. After the intervention period, micro-computed tomography was used to assess the bone morphology at the left tibia and femur. Three-point bending test was used to measure the cortical bone strength at the right tibia and femur.

In both training groups, trabecular number was significantly increased in the proximal tibia, whereas no increase was observed in the distal femur. Trabecular thickness in the proximal tibia and distal femur was significantly increased compared to the control group. The effects on bone strength and morphological parameters were similar in the J10 × 5 and J50 × 1 groups.

The results suggest that 8 weeks of jump training results in site-specific adaptations in cancellous bone morphology in the tibia and femur. However, no effect on bone adaptations was observed by dividing the training into multiple sets.