Characterization of muscle recruitment during gait of bilateral transfemoral and through-knee persons with limb loss

Abstract

Introduction: Due to loss in musculoskeletal capacity, there is an increased burden on the residual limbs of bilateral transfemoral and through-knee persons with limb loss. This reduced capacity is associated with an increased cost of walking that is detrimental to functionality. Compensatory gait strategies are adopted by this population. However, how these strategies relate to specific muscle recruitment is not known. The primary aim of this study is to characterize muscle recruitment during gait of this population. The secondary aim is to assess whether the measured kinematics can be actuated when the endurance of specific muscles is reduced and if this is the case, which alternative muscles facilitate this. Methods: 3D gait data and high-resolution magnetic resonance images were acquired from six bilateral transfemoral and through-knee persons with limb loss. Subject-specific anatomical muscle models were developed for each participant, and a validated musculoskeletal model was used to quantify muscle forces in two conditions: during normal gait (baseline) and when muscles, which were identified as functioning above a "healthy" level at baseline, have a reduced magnitude of maximum force capacity (reduced endurance simulation). To test the hypothesis that there are differences in muscle forces between the baseline trials and the simulations with reduced muscular endurance, a Bonferroni corrected two-way ANOVA with repeated measures was completed between the two states. Results: The baseline analysis showed that the hip flexors experience relatively high muscle activations during gait. The reduced endurance simulation found two scenarios. First, for 5 out of the 12 simulations, the baseline kinematics could not be reproduced with the reduced muscular capacity. Second, for 7 out of 12 cases where the baseline kinematics were achieved, this was possible with compensatory increased activation of some muscles with similar functions (p ≤ 0.003). Discussion: Evidently, due to the loss of the ankle plantar flexors, gait imposes a high demand on the flexor muscle group of the residual limb. This study highlights how the elevated cost of gait in this population manifests in muscle recruitment. To enhance functionality, it is critical to consider the mechanical demand on the hip flexors and to develop rehabilitation interventions accordingly.

Keywords: biomechanics; gait; muscle endurance; muscoskeletal modelling; transfemoral bilateral limb loss.

FIGURE 1

Muscle activations (force normalized to $F_{\mathit{max}}^i)$ over a gait cycle for an individual with bilateral transfemoral limb loss. Muscles are grouped by primary function: flexors, extensors, abductors, and adductors.

FIGURE 2

Maximum muscle activation (force normalized to $F_{\mathit{max}}^i)$ during gait cycle of bilateral transfemoral persons with limb loss. Muscles are categorized as hip flexors, extensors, abductors, and adductors. The box plots show min, max, median, 25 and 75 percentiles, and the outliers. Each subject is plotted in a separate color, and the left legs are represented by ‘►’ and right by ‘◄’.

FIGURE 3

Maximum muscle force normalized to body weight (BW) during gait cycle of bilateral transfemoral persons with limb loss. Muscles are categorized as hip flexors, extensors, abductors, and adductors. The box plots show min, max, median, 25 and 75 percentiles, and the outliers. Each subject is plotted in a separate color, and the left legs are represented by ‘►’ and right by ‘◄’.

FIGURE 4

Normalized muscle force for one bilateral transfemoral person with limb loss for baseline and reduced endurance (RE) condition gait trial (reduce force capacity of the psoas major and adductor longus).

FIGURE 5

Maximum muscle activation (force/ $F_{\mathit{max}}^i)$ over a gait cycle for bilateral transfemoral persons with limb loss participants (baseline in red, reduced endurance state in blue). Baseline values are plotted for only legs for which a feasible solution could be found in the reduced endurance state. A reduced endurance state simulated by a reduction in the maximum capacity of the psoas major and the adductor longus is shown. Muscles are grouped into primary function; p values are presented on a plot for significant difference between the means of baseline and the reduced endurance condition.