THE EFFECTS OF EXTRINSIC MUSCLE FORCES ON THE FOREFOOT-TO-REARFOOT LOADING RELATIONSHIP IN-VITRO - TIBIA AND ACHILLES-TENDON

The effects of muscular activity on the distribution of forces under t he foot, as well as within the foot, are of great importance for deter mining the mechanisms of foot pathologies. Limited data exist concerni ng muscle forces during the gait cycle and the effects of muscle force s conveyed to the ground-reactive forces of the foot. The authors deve loped a cadaveric loading system to determine the effects of force app lied to the Achilles tendon on the forefoot-to-rearfoot loading relati onship in eight cadaveric specimens. The study indicated that, during axial loading of the tibia, force was inherently transferred from the rearfoot to the forefoot. However, the observed forefoot-to-rearfoot l oading relationship did not match the predicted loading relationship f rom a rigid-body diagram, as would be observed in a class I lever. The results indicated that, as the force was increased on the Achilles te ndon, the change in loads on the forefoot and rearfoot was not linear. Specimens with calcaneal inclination angles greater than 20 degrees d emonstrated a more linear increase as compared with those with inclina tion angles less than 20 degrees.