Quantifying mechanical loading and elastic strain energy of the human Achilles tendon during walking and running

Abstract

The purpose of the current study was to assess Achilles tendon (AT) mechanical loading and strain energy during locomotion using a new in vivo approach for measuring AT length that considers the AT curve-path shape. Eleven participants walked at 1.4 m/s and ran at 2.5 m/s and 3.5 m/s on a treadmill. AT length, defined as the distance between its origin at the gastrocnemius medialis myotendinous junction (MTJ) and the calcaneal insertion, was determined experimentally by integrating kinematics and ultrasound analysis. Small foil markers were placed on the skin covering the AT path from the origin to the insertion, and the MTJ, tracked using ultrasonography, was projected to the reconstructed skin to account for their misalignment. Skin-to-bone displacements were assessed during a passive rotation (5 °/s) of the ankle joint and considered in the calculation of AT length. Force and strain energy of the AT during locomotion were calculated by fitting a quadratic function to the experimentally measured tendon force-length curve obtained from maximum voluntary isometric contractions. Maximum AT strain and force were affected by speed (p<0.05, ranging from 4.0 to 4.9% strain and 1.989 to 2.556 kN), yet insufficient in magnitude to be considered an effective stimulus for tendon adaptation. Further, we found a recoil of elastic strain energy at the beginning of the stance phase of running (70-77 ms after touch down) between 1.7 ± 0.6 and 1.9 ± 1.1 J, which might be functionally relevant for running efficiency.

Shorter heels are linked with greater elastic energy storage in the Achilles tendon

“…Finally, because previous studies of how AT moment arm length influences COL have used trained runners running on a treadmill at a speed of 16 km/h, it is still unknown how variation in speed and athletic training impacts elastic loading to the tendon in relation to moment arm length. While previous work has explored elastic loading of the AT at different speeds and under different loading conditions 10 – 21 , this study is the first to investigate the potential correlation between foot geometry like the AT moment arm length and spring-like behavior of this tendon in humans.…”

How Precisely Can Easily Accessible Variables Predict Achilles and Patellar Tendon Forces during Running?

“…A similar study mimicking the patellar tendon force by applying the peak muscle activity in the vasti muscles, demonstrated a similar pattern, although the muscle activity decreased from 18.6 km/h to 25 km/h [26]. Moreover, using a force transducer on the Achilles tendon, Kharazi et al [27] demonstrated that the Achilles tendon peak force grows linearly from 5-12.6 km/h. With a similar method, Komi [28] demonstrated that the Achilles tendon peak force was increasing until around 21 km/h (6 m/s) and thereafter decreasing at higher speeds.…”