Article

Defective muscle coordination for balance recovery may contribute to stroke
survivors' propensity for falling. Thus, we investigated deficits in muscle
coordination for postural control and their association to body sway following
balance perturbations in people with stroke. Specifically,
we compared the
automatic postural responses of 8 leg and trunk muscles recorded bilaterally in
unimpaired individuals and those with mild to moderate impairments after
unilateral supratentorial lesions (>6 months). These responses were elicited by
unexpected floor translations in 12 directions. We extracted motor modules (ie,
muscle synergies) for each leg using nonnegative matrix factorization. We also
determined the magnitude of perturbation-induced body sway using a single-link
inverted pendulum model. Whereas the number of motor modules for balance was not
affected by stroke, those formed by muscles with long latency responses were
replaced by atypically structured paretic motor modules (atypical muscle
groupings), which hints at direct cerebral involvement in long-latency feedback
responses. Other paretic motor modules had intact structure but were poorly
recruited, which is indicative of indirect cerebral control of balance.
Importantly, these paretic deficits were strongly associated with postural
instability in the preferred activation direction of the impaired motor modules.
Finally, these deficiencies were heterogeneously distributed across stroke
survivors with lesions in distinct locations, suggesting that different cerebral
substrates may contribute to balance control. In conclusion, muscle coordination
deficits in the paretic limb of stroke survivors result in direction-specific
postural instability, which highlights the importance of targeted interventions
to address patient-specific balance impairments.

Langue : ANGLAIS