Strenuous exercise-induced remodelling of mature bone: relationships between in vivo strains and bone mechanics.

Mature bone can adapt to strenuous exercise, but no study has correlated the changes in bone in vivo strains, remodelling and mechanical properties that occur as a consequence of strenuous training. Therefore, we examined exercise-related remodelling and in vivo strains in the tarsometatarsus (TMT) of three groups of adult (post-physial closure) White Leghorn roosters: basal control (30 weeks of age), age-matched control (39 weeks) and exercise (39 weeks). Exercise birds ran for 1 h a day, 5 days a week for 9 weeks at 70-75% of predicted maximum aerobic capacity. During treadmill locomotion, in vivo strains were recorded from miniature rosette strain gauges implanted on anterior, medial and lateral TMT cortices. TMT mechanical properties were measured with three-point bending tests to failure. Cortical morphometry was digitized from photographic slides of a 1-mm thick mid-diaphysial cross section of each bone. Exercise and age-matched control TMTs had significantly greater cortical area and maximum load than had basal controls. Exercise axial strains significantly exceeded basal and age-matched control strains along the anterior and lateral surfaces. Age-matched control anterior axial strain was twice that of the basal control. The mature bone remodelling suggested that the structural properties optimized by exercise-induced remodelling may differ from those optimized by age-related remodelling. The findings support the osteoregulatory role of strain but contradict earlier data suggesting that strain magnitudes do not change significantly with age or exercise.