Antagonist Activation Measurement at the Ankle Using High-density and Bipolar Surface EMG in Chronic Hemiparesis

Muscle Hypertonia, Spasticity, Muscle, Stroke

In chronic hemiparesis, abnormal antagonist muscle activation in the paretic lower limb contributes to impair ambulation capacities. A biased estimate of antagonist muscle activation when using surface bipolar EMG compared with high-density (HD) EMG has been previously reported in healthy subjects. The present study compares muscles cocontraction at the paretic ankle estimated with a pair of and multi-channel surface EMG.

In chronic hemiparesis, gait velocity deficit is associated with a disturbed voluntary movement caused especially by inappropriate antagonist muscle activation. The present study investigates muscles cocontraction at the paretic ankle estimated with a pair of and multi-channel surface EMG (HD-EMG) in patients after stroke. HD-EMGs were collected from gastrocnemius medialis (GM), tibialis anterior (TA) and soleus (SO) during isometric contractions. From these EMGs the study asked whether bipolar and HD-EMGs provided comparable estimates of antagonist activation. Two active contraction levels (submaximal vs. maximal) and knee positions (flexed vs. extended) were assessed for each muscle. Notwithstanding the evidence of localized antagonist activation in the GM muscle of healthy subjects, hypothesizing equally localized antagonist activation in the paretic limb may not follow from the current literature. In virtue of evidence supporting the enlargement of motor unit territories in paretic and hyperactive muscles, it may be that stroke survivors have lost their ability to regionally and appropriately activate their muscle. In this case, bipolar and HD-EMG would be expected to provide comparable antagonist activation coefficients.

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