Data from: Fascicles from energy-storing tendons show an age-specific response to cyclic fatigue loading

Some tendons, such as the human Achilles and equine superficial digital
flexor tendon (SDFT), act as energy stores, stretching and recoiling to
increase efficiency during locomotion. Our previous observations of
rotation in response to applied strain in SDFT fascicles suggest a helical
structure, which may provide energy-storing tendons with a greater ability
to extend and recoil efficiently. Despite this specialization,
energy-storing tendons are prone to age-related tendinopathy. The aim of
this study was to assess the effect of cyclic fatigue loading (FL) on the
microstructural strain response of SDFT fascicles from young and old
horses. The data demonstrate two independent age-related mechanisms of
fatigue failure; in young horses, FL caused low levels of matrix damage
and decreased rotation. This suggests that loading causes alterations to
the helix substructure, which may reduce their ability to recoil and
recover. By contrast, fascicles from old horses, in which the helix is
already compromised, showed greater evidence of matrix damage and suffer
increased fibre sliding after FL, which may partially explain the
age-related increase in tendinopathy. Elucidation of helix structure and
the precise alterations occurring owing to both ageing and FL will help to
develop appropriate preventative and repair strategies for tendinopathy.