Article

Resistive exercise after stroke can improve strength
(force-generating capacity) without increasing spasticity (velocity-dependent
hypertonicity). However, the effect of resistive load type on muscle activation
and co-contraction after stroke is not clear. OBJECTIVE: The purpose of this
study was to determine the effect of load type (elastic, viscous, or mass) on
muscle activation and co-contraction during resisted forward reaching in the
paretic and nonparetic arms after stroke. DESIGN: This investigation was a
single-session, mixed repeated-measures pilot study. METHODS: Twenty participants
(10 with hemiplegia and 10 without neurologic involvement) reached forward with
each arm against equivalent elastic, viscous, and mass loads. Normalized shoulder
and elbow electromyography impulses were analyzed to determine agonist muscle
recruitment and agonist-antagonist muscle co-contraction. RESULTS: Muscle
activation and co-contraction levels were significantly higher on virtually all
outcome measures for the paretic and nonparetic arms of the participants with
stroke than for the matched control participants. Only the nonparetic shoulder
responded to load type with similar activation levels but variable co-contraction
responses relative to those of the control shoulder. Elastic and viscous loads
were associated with strong activation; mass and viscous loads were associated
with minimal co-contraction. LIMITATIONS: A reasonable, but limited, range of
loads was available. CONCLUSIONS: Motor control deficits were evident in both the
paretic and the nonparetic arms after stroke when forward reaching was resisted
with viscous, elastic, or mass loads. The paretic arm responded with higher
muscle activation and co-contraction levels across all load conditions than the
matched control arm. Smaller increases in muscle activation and co-contraction
levels that varied with load type were observed in the nonparetic arm. On the
basis of the response of the nonparetic arm, this study provides preliminary
evidence suggesting that viscous loads elicited strong muscle activation with
minimal co-contraction. Further intervention studies are needed to determine
whether viscous loads are preferable for poststroke resistive exercise programs.

Langue : ANGLAIS