Global lower limb muscle coactivation during walking in trans-femoral and trans-tibial amputees

The aim of this work was to analyze the global coactivation (mechanism that regulates the simultaneous activity of antagonist muscles around the same joint) of the sound limb in people with unilateral trans-femoral and transtibial amputation in order to understand how the nervous system manages different levels of amputation and different types of prostheses. To achieve this aim, we calculated the global coactivation of 12 muscles using a time-varying multi-muscle co-activation function in 25 subjects with unilateral trans-femoral amputation (7, 12 and 6 with mechanical, electronic and bionic prosthesis respectively), in 7 subjects with trans-tibial amputation and in 20 healthy subjects representing the control group. The results highlight that, both trans-tibial and trans-femoral amputees show a characteristic double-peak shape as in healthy subjects although the second peak, in particular in subjects with trans-femoral amputation, appears to be slightly delayed with respect to the one that characterizes the control subjects. Furthermore, there is greater variability for both samples of amputees, with respect to the control subjects. On the other hand, TFA patients adopt similar strategies regardless of the kind of prosthesis. These results might indicate that the CNS has to manage, through the sound limb, a higher complexity due to double prosthetic joint of the amputated limb during the transfer to it of the body weight and all the control strategies that the patient adopts in response to the reorganization of the sensorimotor system as a consequence of the amputation. These findings suggest that the global lower limb coactivation behavior could be a useful measure of the motor control strategy, limb stiffness, postural stability in subjects with lower limb amputation.