Multiscale investigation on the effects of additional weight bearing in combination with low-magnitude high-frequency vibration on bone quality of growing female rats

Abstract

This study aimed to explore the effects of additional weight bearing in combination with low-magnitude high-frequency vibration (LMHFV; 45 Hz, 0.3 g) on bone quality. One hundred twenty rats were randomly divided into ten groups; namely, sedentary (SED), additional weight bearing in which the rat wears a backpack whose weight is x% of the body weight (WBx; x = 5, 12, 19, 26), basic vibration (V), and additional weight bearing in combination with LMHFV in which the rat wears a backpack whose weight is x% of the body weight (Vx; x = 5, 12, 19, 26). The experiment was conducted for 12 weeks, 7 days per week, and 15 min per day. A three-point bending mechanical test, micro computed tomography, and a nanoindentation test were used. Serum samples were analyzed chemically. Failure load in V19 rats was significantly lower than that in SED rats (P < 0.05). Vx (x = 5, 12, 19, 26) rats showed poor microarchitectures. The content of tartrate-resistant acid phosphatase 5b was significantly higher in Vx (x = 5, 12, 19, 26) rats than that in SED rats (P < 0.05). V26 rats demonstrated comparatively better nanomechanical properties of materials than the other vibrational groups. Additional weight bearing in combination with LMHFV negatively affected the macromechanical properties and microarchitecture of bone. Heavy additional weight bearing, such as 26% of body weight, in combination with LMHFV was able to improve the nanomechanical properties of growing bone material compared with LMHFV. A combined mechanical stimulation was used, which may provide useful information to understand the mechanism of this mechanical stimulation on bone.

Possible effects of whole body vibration on bone properties in growing rats

“…However, WBV was reported to improve bone mass and structure by increasing bone formation or decreasing bone resorption in both normal and osteopenia rodents older than 4 weeks [[13], [14], [15], [16], [17]]. On the other hand, the effects of WBV on bone properties were inconsistent among young rodents under the age of 4 weeks [18,19]. One study previously reported that femoral stiffness and yield load are significantly increased by 45-Hz WBV (0.3 g , 15 min/d, 5 d/wk) for 5 weeks in wild-type female mice compared with those of wild-type female mice without WBV [19].…”

“…One study previously reported that femoral stiffness and yield load are significantly increased by 45-Hz WBV (0.3 g , 15 min/d, 5 d/wk) for 5 weeks in wild-type female mice compared with those of wild-type female mice without WBV [19]. In contrast, another study previously reported that BMD and BV/TV of the femoral head and BMD of the femoral cortical bone are decreased by 45-Hz WBV (0.3 g , 15 min/d, 7 d/wk) for 12 weeks in 4-week-old normal female rats [18]. It should be noted that the WBV conditions excluding the intervention period and intervention days per week were the same in these 2 studies.…”

“…Likewise, positive effects on bone mechanical properties were observed in rats which underwent WBV (5 d/wk) for 5 weeks [19]. On the contrary, daily WBV (7 d/wk) for 12 weeks negatively affected bone mass and TBMS parameters [18]. In that particular study, the negative effects of WBV were probably caused by an excess of bone resorption over bone formation, which was evidenced by the decreased ALP and increased TRACP-5b levels.…”

“…In animal studies, WBV was found to increase bone mass and improve structural parameters in young rodents (aged ≤8 weeks) with spinal cord injury, unloading or ovariectomy [[13], [14], [15]]. On the other hand, a few studies examined the potential effects of WBV on bone mass in normal young rodents [[16], [17], [18]]. In 7-week-old male mice, WBV (90 Hz, 2 g , 15 min/d, 5 d/wk) for 3 weeks increased femoral trabecular bone cellular activity, femoral cortical thickness, and cross-sectional area, and subsequently WBV for 9 weeks increased femoral cortical tissue mineral density (TMD) [16].…”

“…In addition, WBV (45 Hz, 0.3 g , 15 min/d, 5 d/wk) for 5 weeks increased femoral mechanical strength in 3-week-old wild-type female mice, and also increased the tibial trabecular bone fraction in 3-week-old female mice with osteogenesis imperfecta [19]. However, in 4-week-old female rats, WBV (45 Hz, 0.3 g , 15 min/d, 7 d/wk) for 12 weeks did not affect femoral bone mass, structure or mechanical strength [18].…”