Aging and the effects of a half marathon on Achilles tendon force–elongation relationship
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 (50–67 years) and 22 younger (21–29 years) participants ran a 21 km route at their own pace (mean and SD: old: 3.1 ± 0.3 m s−1; young: 3.6 ± 0.5 m s−1). We tested for changes in the AT force–elongation relationship using dynamometry and ultrasonography during isometric voluntary ankle plantarflexion ramp contractions, conducted 20–28 h pre-run, immediately pre-run, immediately post-run and 20–28 h 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 20–28 h 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 20–28 h 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 20–28 h post-run, suggesting that a tendon viscoelastic recovery mechanism may occur in vivo.
KeywordsTendon stiffness Tendon fatigue Running Mechanical loading Age Muscle contraction
20–28 h before the run
Within 20–28 h after the run
Analysis of variance
Immediately before the run
Immediately after the run
Maximal voluntary plantarflexion ramp contraction
The Bundesinstitut für Sportwissenschaft (BISp), the Olympiastützpunkt Rheinland and the Forschungsservicestelle of the German Sport University Cologne (Hochschulinterne Forschungsförderung) provided the funding for this study. In addition, we would like to thank Dr. Falk Schade for his support throughout this research project.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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