Force- and moment-generating capacity of lower-extremity muscles before and after tendon lengthening.
A computer model of the human lower extremity was developed to study how surgical lengthening of tendon affects the force- and moment-generating capacity of the muscles. This model computes the maximum isometric force and the resulting joint moments that each muscle-tendon complex can develop at any body position. Tendon lengthenings were simulated by increasing the tendon length of each muscle-tendon complex and computing the change in the maximum isometric muscle force and joint moments at a specific body position. These simulations showed that the forces and moments developed by the ankle plantarflexors are extremely sensitive to changes in tendon length. For example, at a body position corresponding to the midstance phase of gait, the maximum isometric moment generated by soleus decreased 30% with a 1-cm increase in tendon length, and 85% with a 2-cm increase in tendon length. In contrast, 1- and 2-cm increases in iliopsoas tendon length decreased its hip flexion moment by only 4% and 9%, respectively. This article quantifies the sensitivity of muscle force and joint moments to changes in tendon length for the most commonly lengthened lower-extremity tendons. These results indicate how much each of these tendons should be lengthened to achieve an incremental decrease in muscle force or joint moment.
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Biomedical Engineering Department, Northwestern University, Evanston, Illinois.
Zajac
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D000843:Ankle Joint / Q000502:physiology; D003196:Computer Graphics; D003198:Computer Simulation; D006621:Hip Joint / Q000502:physiology; D006801:Humans; D007537:Isometric Contraction; D007719:Knee Joint / Q000502:physiology; D008954:Models, Biological; D009068:Movement; D009132:Muscles / Q000502:physiology; D013710:Tendons / Q000601:surgery*