Muscle compensatory mechanisms during able-bodied toe walking.

The purpose of this study was to use muscle-actuated forward dynamic simulations to quantify individual muscle contributions to body support (vertical ground reaction force) and propulsion (horizontal ground reaction force) and the mechanical energetics of the body segments during toe and heel-toe walking performed by able-bodied subjects to identify possible compensatory mechanisms necessary to toe walk. The simulations showed that an increased magnitude of plantar flexor power output in early stance, which was necessary to maintain the equinus posture during toe walking, contributed to body support and acted to brake (decelerate) the center-of-mass in the horizontal direction. This in turn required a reduction in the contributions to support from the vastii, gluteus maximus and biarticular hamstring muscles and decreased contributions to braking from the vastii and to a lesser extent the gluteus maximus. In late stance, the soleus contributed less to body support and forward propulsion during toe walking, which when combined with the increased braking by the plantar flexors in early stance, required a prolonged contribution to forward propulsion from the hamstrings from mid- to late stance. The multiple compensatory mechanisms necessary to toe walk have important implications for distinguishing between underlying pathology and necessary compensatory mechanisms, as well as for identifying the most appropriate treatment strategy for equinus gait.