Muscle activity and postural control during standing of healthy adults wearing a simulated trans-femoral prosthesis

[Purpose] It is unknown what compensatory strategies are employed by amputees during standing at the initial stage of prosthesis wearing. This study examined the muscle activity during standing with different positions of center of gravity (COG) of healthy subjects wearing a simulated trans-femoral prosthesis on the right leg for the first time. [Subjects] Eight healthy subjects participated in this study. [Methods] Electromyograms of the left lower limb muscles were recorded during standing with different COG conditions. Center of pressure was also measured using a force platform. [Results] There were significant differences among the standing conditions for all the muscles. The tibialis anterior and gastrocnemius were mainly activated in weight shift backward and forward, respectively, which suggests that stiffness of ankle muscles, an ankle strategy, is related to maintaining balance. Significant activity of the semitendinosus, vastus medialis and lateralis also occurred, which indicates that an additional hip strategy was also employed for the sound leg during standing. In addition, there were significant differences of total sway path between shift backward and the other standing conditions. [Conclusion] Fear of falling and lack of sensory feedback may affect standing balance control, particularly in shift backward. Subjects will employ/develop a hip strategy as a compensatory mechanism due to peripheral dysfunction and fear of falling at the first experience of prosthetic standing.