Aging and the effects of a half marathon on Achilles tendon force-elongation relationship.

Abstract

We aimed to determine whether there are different changes in Achilles tendon (AT) mechanical properties in middle-aged, compared to younger runners that might indicate that tendon fatigue, induced by long-distance running, is age-dependent. 27 middle-aged (50-67years) and 22 younger (21-29years) participants ran a 21km route at their own pace (mean and SD: old: 3.1±0.3ms-1; young: 3.6±0.5ms-1). We tested for changes in the AT force-elongation relationship using dynamometry and ultrasonography during isometric voluntary ankle plantarflexion ramp contractions, conducted 20-28h pre-run, immediately pre-run, immediately post-run and 20-28h post-run. Stride frequency and number were examined to estimate cyclic tensile loading characteristics of the tendon during running. Muscle strength decreased significantly (P<0.05) in both groups immediately post-run (old: 17%; young: 11%) and recovered to baseline within 20-28h post-run. AT stiffness did not change for the younger adults, whereas the middle-aged adults showed a significant (P<0.05) decrease in AT stiffness (22%). However, tendon stiffness recovered to baseline 20-28h post-run. Middle-aged, compared to young adults, demonstrated significantly (P<0.05) greater stride frequency and number, but no correlations with tendon fatigue changes were determined (R 2≤0.038). The results suggest that the plasticity of the AT in response to short-term mechanical loading may be age dependent and that the AT length-tension properties of middle-aged runners may be more vulnerable to change following running compared to younger athletes. However, the observed AT changes in the middle-aged runners dissipated within 20-28h post-run, suggesting that a tendon viscoelastic recovery mechanism may occur in vivo.