The reaction strategy of lower extremity muscles when slips occur to individuals with trans-femoral amputation

The aim of this study is to investigate the surface electromyography (sEMG) responses of lower extremity muscles for both healthy people and individuals with trans-femoral amputation (TFA), when slip events occur during level walking. Six male individuals with unilateral TFA and five healthy subjects participated in this study. Each subject was required to walk at a self-selected comfortable pace along a 5 m plastic walkway, and to perform walking trials on dry and oily conditions respectively. The sEMG signals of muscles on legs and around waist were recorded in each trial and the normalized instantaneous muscle power (IMP) values were employed to quantify the response intensity. The IMP profiles of each muscle in oily-surface walking trials were compared quantitatively with that in dry-surface trials. There are three main findings in this study. (1) Different muscle reaction strategies are employed in slip events by the healthy persons and the individuals with TFA, respectively. Moreover, when the slip event occurs on the prosthetic leg and the intact leg of the individuals with TFA respectively, the muscle reaction strategies are also different. (2) The individuals with TFA face higher risks of fall than the healthy persons no mater slips occur on the prosthetic side or the intact side. (3) The hip muscles, especially the gluteus maximus (GMA) muscles, always enormously contribute to posture adjustment and balance recovery in slip events.