Causal Inference Predicts that Muscle Excitation is Both a Contributor and Response to Frontal Plane Dynamic Balance...

More than 50% of individuals with lower-limb amputations and ~40% of older individuals (over 65 years old) fall each year. To optimize prosthetic intervention for fall prevention, it is important to understand the neuromotor control of balance. We use a data-driven approach, Convergent Cross Mapping, to determine the relationships between lower-limb muscle excitation and whole-body and segmental angular momentum in the frontal plane. These relationships were determined for 10 able-bodied older individuals and 13 older individuals with transtibial amputations at normal and fast walking speeds. The results suggest that there were several group and group-speed interaction differences, especially in the medial hamstrings of the intact and amputated legs at normal speeds, which exhibited stronger relationships between muscle activity and momentum of the whole-body, trunk and arms relative to control subjects. Difference between the subject group interlimb coupling was also observed by the stronger contribution of the gastrocnemius in the intact limb to frontalplane momentum of the contralateral arm for persons with limb loss. Nearly equal numbers of relationships at both speeds showed muscle activities of the lower extremity were most predictive of subsequent (i.e., future), current or previous states of angular momentum, suggesting that muscle activity is responsible for generation, regulation and likely a response of/to dynamic balance in the frontal plane, respectively. Finally, this approach analyzes the functional outcomes of prosthetic intervention and how amputation alters the neuromotor control of gait in older individuals. This analysis can be applied at the individual level to study effects of prosthesis selection.