Bone Abstracts

Bones’ fracture resistance is achieved in vivo by adaptation to habitual loading. Aged bone can adapt to exercise¹ but in female rodents ageing impairs the adaptive response to artificial loading^2,3. This inconsistency led us to investigate whether treadmill exercise, sufficiently mild to not itself stimulate new bone formation, could rescue aged bone’s diminished response to artificial loading.

Young adult 17-week-old (YF) and aged 19-month-old (AF) female C57Bl/6 mice received artificial tibial loading only or loading plus mild levels of treadmill exercise. After treadmill acclimatization, mice were exercised for 30 min every other day at voluntary running speeds (YF 23 cms⁻¹, AF 18 cms⁻¹)⁴ for 2 weeks. 3 h later, their right tibiae were subjected to a short period of axial non-invasive loading; 40 cycles, peak strain 2250 με; left limbs were internal controls⁵. Bone was assessed using μCT, serum IGF1 by ELISA, serum corticosterone by RIA.

Artificial loading increased cortical bone area and thickness in YF and AF and trabecular BV/TV and thickness in YF. Exercise had no effect on the cortical response to loading but in YF reduced the loading-related increase in trabecular BV/TV (−32.1%, P<0.05). Exercise in YF also increased serum IGF1(15.0%, P<0.05). In AF exercise decreased serum corticosterone (−48.1%, P<0.05) and increased periosteally-enclosed area by 8.9% (P<0.01) in AF.

This suggests that mild exercise, which would be expected to have beneficial effects in muscle, has no effect on bone’s response to almost concurrent loading in young mice and in aged mice does not rescue their diminished response to loading. The beneficial effects of exercise in the elderly are thus likely to reflect local adaptation to mechanical strain rather than to effects derived from muscle.

References: 1. Lepannen et al. PLoS ONE 2008.

2. Turner et al. JBMR 1995.

3. Srinivasan et al. Bone 2003.

4. Parkhouse et al. Age 1995.

5. Sugiyama et al. JBMR 2012.