SMITH, R.K.W.*; GOODSHIP, A.E.: The Influence of Ageing and Exercise on Tendon Matrix: Hypotheses for the Initiation and Prevention of Strain-induced Tendinopathies

Tendon strain injuries are common in human and equine athletes. In horses, in vitro strain measurements at rupture are close to in vivo measurements at the gallop. Small decreases in matrix quality will therefore increase the risk of tendinopathy substantially. Epidemiological studies in horses and man have demonstrated a close association between lesion incidence and both age and exercise, frequently with bilateral lesions identified ultrasonographically in both species. Therefore progressive tendon degeneration may precede clinical tendinopathy. Age and exercise, acting synergistically, caused regional reductions in collagen fibril crimp in equine energy-storing tendons. A higher proportion of small collagen fibrils was found in long-term exercised older horses, but not in short-term exercised younger horses. This did not correlate with new collagen formation and thus may result from disassembly of larger diameter fibrils. Cartilage Oligomeric Matrix Protein (COMP) levels were low in neonates but increased in response to loading until they peaked at skeletal maturity. Mechanical properties were related to COMP levels at this age. Levels subsequently declined which was accelerated by exercise. There was high expression of TGFbeta in young equine tendon, declining after skeletal maturity, while tenocytes showed similar responses to growth factors in vitro irrespective of age. We therefore hypothesise that tensional weight-bearing tendon can adapt to exercise during development but has little ability to do so after skeletal maturity, possibly due to a lack of growth factors rather than cellular senescence. Exercise accelerates the ageing effect of cumulative degeneration after skeletal maturity.