Abstract
BackgroundBone tissue displays a hierarchical organization. Mechanical environments influence bone mass and structure. This study aimed to explore the effects of different mechanical stimuli on growing bone properties at macro–micro–nano scales.MethodsSixty five-week-old female Wistar rats were treadmill exercised at moderate intensity with the speed of 12 m/min, and then randomly divided into five groups according to weight-bearing level. After 8 weeks of experiment, femurs were harvested to perform multiscale tests.ResultsBone formation was significantly increased by weight-bearing exercise, whereas bone resorption was not significantly inhibited. Trabecular and cortical bone mineral densities showed no significant increase by weight-bearing exercise. The microstructure of trabecular bone was significantly improved by 12% weight-bearing exercise. However, similar positive effects were not observed with further increase in weight-bearing levels. The nanomechanical properties of trabecular bone were not significantly changed by weight-bearing exercise. The macrostrength of whole femur and the nanomechanical properties of cortical bone significantly decreased in the 19% and 26% weight-bearing exercise groups.ConclusionWhen rats ran on the treadmill at moderate intensity during growth period, additional 12% weight-bearing level could significantly increase bone formation, improve microstructure of trabecular bone, as well as maintain the structure and mechanical properties of cortical bone. Excessive weight-bearing level caused no positive effects on the trabecular bone microstructure and properties of cortical bone at all scales. In addition, increased weight-bearing level exerted no significant influence on trabecular and cortical bone mineral densities.
Highlights
The effect of treadmill exercise on bone mass is associated with the peak strain on the bone produced by exercise; and animal studies have reported that once the mechanical strain induced by exercise exceeds a certain threshold, bone formation is positively correlated with the peak strain magnitude [10,11,12]
All rats were subjected to continuous treadmill exercise at moderate intensity with different weightbearing levels for 8 weeks, the bilateral femurs were evaluated by multiscale methods, and the effects of different weight-bearing levels on bone quality were comprehensively analyzed
We confirmed that additional 12% weight-bearing level can significantly increase bone formation, improve microstructure of trabecular bone, and maintain structure and mechanical properties of cortical bone when female rats were treadmill exercised at moderate intensity during the growth period
Summary
Running is one of the most common weight-bearing exercises and it can increase bone mass in humans and animals [1,2,3,4,5]. A previous study reports that moderate-intensity treadmill exercise with a 19–20% body weight backpack can significantly increase bone mineral content in the hind limbs of 5-month-old female rats [18]. This form of exercise significantly increases the bone mineral density (BMD) and bone mineral content of trabecular bone in 3-month-old ovariectomized female rats [19]. Moderate treadmill exercise in combination with a certain additional load in backpack may effectively increase bone mass in adult rats
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