PASSIVE REGULATION OF IMPACT FORCES IN HEEL-TOE RUNNING

Objective. the purpose of this study was to determine whether passive mechanisms can account for impact force regulation with changing shoe hardness. Design. A three-dimensional musculoskeletal model of the low er extremity was developed to simulate impact in running with two diff erent shoe hardnesses. Background. Considerable research has focused o n developing shoe cushioning to reduce impact forces. However, only mi nimal changes in peak external impact force have been observed with ch anges in shoe hardness. It is hypothesized that passive mechanisms can regulate impact forces with changing shoe hardness, without changing muscle activities. Methods. Initial kinematic inputs for the simulatio ns were measured from nine male subjects performing heel-toe running. Simulations were performed with initial conditions and muscle stimulat ion patterns held constant while shoe hardness was varied between a ha rd and a soft condition. Results. There was no significant difference between the soft and hard shoe peak impact forces. Peak rates of loadi ng were greater for the hard shoe than the soft shoe. Muscle forces ch anged with shoe conditions. For some muscles (including the tibialis a nterior) the forces were greater for the hard shoe, whereas for other muscles (including the peroneus) forces were greater for the soft shoe condition. Conclusions. Peak impact forces with changing shoe conditi ons can be regulated by passive mechanical changes without changing mu scle activities or kinematics before touchdown.