Effects of two exercise modalities and subsequent detraining on trabecular bone microarchitecture in growing male rats.

Weight-bearing and high-impact exercise during growth enhance bone accrual; however, the extent to which these benefits persist after detraining remains unclear. This study examined the effects of detraining after treadmill running and jump exercise on trabecular bone microarchitecture and strength in growing rats. Ninety male Wistar rats were assigned to control, running, or jump groups (n = 30 each) and trained for 8 weeks, followed by 0, 12, or 24 weeks of detraining. Running was performed at 25 m/min for 60 min/day, and jump training consisted of 10 jumps/day (40 cm), both conducted 5 days/week. Distal femoral trabecular microarchitecture, volumetric bone mineral density (vBMD), and finite element analysis-derived fracture load were assessed using micro-computed tomography. Both exercise modalities increased trabecular bone volume fraction, thickness, number, vBMD, and fracture load compared with controls (all p < 0.05-0.001). Jump exercise preferentially increased trabecular thickness, whereas running was associated with higher trabecular number. These benefits were largely maintained for up to 12 weeks after exercise cessation but were no longer evident after 24 weeks of detraining. These findings suggest that exercise-induced improvements in trabecular bone during growth are partially lost following exercise cessation, suggesting continued mechanical loading is required to maintain these adaptations.