Meeting Abstract
Tendons play a crucial role in vertebrate locomotion, functioning as springs which allow elastic energy storage and release. Consequently, these biological springs can function in power amplification during accelerations, power attenuation during decelerations and recycling energy within a stride during steady, level running. These functions are aided by low hysteresis of the loading-unloading curve, with 90% or more of energy stored in the tendon being returned during unloading. During loading, tendons initially have a low-stiffness “toe region”, followed by a high-stiffness linear region, each mediated by different processes. To determine whether hysteresis varies with strain and frequency, we isolated mouse Achilles tendons and subjected them to sinusoidal length changes while recording force. Both strain and frequency had minimal effects on hysteresis, but hysteretic energy losses were consistently high, with between 35-45% of the loaded energy being lost. This high hysteretic energy loss differs tremendously from the <10% loss seen in other species. Replication of methods on rubber samples showed 10% low energy loss, and there was no evidence of knot slip, fatigue or damage during the trials. In subsequent replication experiments, ink marks on the tendon were tracked via video, but no strain heterogeneity was observed. Similar results have been published by other labs for mouse Achilles and tibialis anterior tendons and rat tail tendons. Such large hysteretic losses may contribute to the limited use of elastic energy storage in rodents during locomotion.
