A novel approach to assess coordination in people with transtibial amputations using continuous and event relative phase

Continuous relative phase (CRP) quantifies coordination for cyclic motions as the difference in the phase portrait locations between its constituent coordinates and has been widely used in populations with neuromuscular impairments. Continuous analyses, like statistical parameter mapping (SPM), provide greater resolution than traditional techniques that first compress CRP across a section of the cycle to a single point, like mean average relative phase (MARP). However, both analyses neglect the effect of intermediate event timing (e.g. toe-off), on coordination. Given this deficit and the notion that some people with transtibial amputations (PwTA) may not benefit from powered prostheses due to altered coordination, we computed lower extremity CRPs from 5 PwTA walking with their own passive prostheses and a powered device on a treadmill, as well as 5 matched able-bodied individuals (ABI). We then compared results from non-parametric SPMs to those from MARP using a 10-40-10-40 gait phase decomposition and extracted relative phase at the events that theoretically delineate the decomposition. We found continuous, discrete analyses matched well, particularly near ankle "push-off" (∼55 % gait cycle) with all methods identifying differences in shank-foot coordination between the ABI group and PwTA group walking with the powered device. Although it is unclear why the powered prosthesis promotes more in-phase shank-foot CRP, potential covariates include limb posture and device control. In tandem with altered event timing, these factors may not only influence coordination, but also illuminate why some PwTA do not reduce their energy expenditure when walking in powered ankle prostheses.