Deficient Muscle Coordination Patterns of Reactive Stepping Responses in People With Chronic Stroke.

Background: People with stroke often have persistent balance impairments that have a profound impact on mobility and daily life independence. Several studies have been conducted to identify stroke-related deficits in neuromuscular responses to balance perturbations. Yet, the majority of these studies involved low-intensity, non-stepping perturbations, whereas falling typically occurs at high-intensity perturbations where stepping is a key saving strategy.

Objective: We aimed to identify deficits in muscle coordination patterns of reactive stepping in people with supratentorial stroke (PwS).

Methods: We included 32 PwS, who performed multidirectional stepping responses with their paretic and non-paretic leg. We determined step quality, and performed muscle synergy analysis to characterize stance- and swing-leg muscle coordination patterns.

Results: We observed smaller leg angles in PwS in lateral, posterolateral and posterior directions, particularly with the paretic leg. Muscle synergy analysis yielded a set of 5 synergies in both groups for the swing VAF_Paretic = 0.84 ± 0.02, VAF_Non-Paretic = 0.84 ± 0.02) and stance leg VAF_Paretic = 0.85 ± 0.02, VAF_Non-Paretic = 0.84 ± 0.02). Three synergies were less frequently represented during paretic step execution. In addition, for the synergy with prominent gluteus medius involvement, underrepresentation was associated with lower Fugl-Meyer lower-extremity scores.

Conclusions: The finding of deficient synergy structure and activation during reactive stepping complements and extends insights into balance related impairments after stroke. As the key next step, the methodology presented here allows identifying whether training-induced gains in reactive step quality are related to optimization of pre-existing coordination patterns, or whether some degree of behavioral restitution (i.e., return to "normal" coordination patterns) may still be possible.