Abstract
The dorsal movement of the Achilles tendon during ankle rotation is restricted by anatomical obstructions. Previously, we demonstrated that the anatomical obstruction provides a gain (gainAT) in the proximal displacement of the calcaneus compared to the change in the Achilles tendon length. Here, we empirically validate and extend our previous modeling study by investigating the effects of a broad range of obstruction locations on gainAT. The largest gainAT could be achieved when the obstruction was located on the most ventral and distal sides within the physiological range of the Achilles tendon, irrespective of the ankle position.
Highlights
The movement of the foot during ankle plantarflexion is amplified compared with the shortening of the plantarflexor muscles
Gans [2] suggested that a pennate fiber arrangement between the aponeuroses, which remain at a constant distance from each other during contraction, results in a movement of the aponeurosis parallel to the long axis of the muscle, which is amplified compared with the shortening of the muscle fiber
We investigated the effects of a broad range of inflection point locations on the gain from the Achilles tendon (gainAT) during ankle rotation at the two positions
Summary
The movement of the foot during ankle plantarflexion is amplified compared with the shortening of the plantarflexor muscles. Variations in the aponeurosis separation (i.e., muscle thickness) before contraction varies the gain such that the aponeuroses moving closer together decrease the gain, and those moving further apart increase the gain [3], a mechanism that becomes important during muscle atrophy that accompanies aging These two effects are insufficient to completely account for the overall amplification. Hodgson et al [3] first introduced the concept of a rigid restriction on the dorsal movement of the Achilles tendon due to the presence of a fixed inflection point or bend in the tendon during ankle plantarflexion They demonstrated through simulation that this inflection point or bend in the tendon results in an amplification of the proximo-distal displacement of the calcaneus (the distal endpoint of the Achilles tendon) relative to the myotendinous junction between the soleus muscle and the Achilles tendon (proximal start point of the Achilles tendon). The present study conducted a modeling investigation, because it was difficult to identify the location of the inflection point within the Achilles tendon that exhibits the largest gainAT within the physiological range of the Achilles tendon using an in vivo human experimental study
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