It has been inferred that stroke-induced alterations of the lower motor neurons and their muscle fibres may contribute to muscle weakness and thus to motor impairment. Although previous accounts have investigated the mechanisms underpinning muscle weakness from muscle fiber conduction velocity estimates, reports about how the global conduction velocity (CV) differ between healthy and paretic muscles post-stroke are uncommon. Thus, in this study we examined side-differences in global CV estimates from biceps brachii muscles of stroke survivors, and their relation with differences between muscles’ functions.

Seven chronic post-stroke patients participated in this study. Surface electromyograms were sampled with a grid of 32 electrodes (8×4; 10mm inter-electrode distance) from biceps brachii. Stimulation electrodes were placed in bipolar configuration as proximally as possible over the muscle. CV values were estimated from differential M waves elicited by supramaximal current pulses. Impairment of biceps brachii functions was assessed with the Fugl-Meyer Assessment scale. Spearman's rank-order correlation was applied to verify the relationship of the healthy/paretic ratio values for CV and Fugl-Meyer values.

There was a significant negative correlation (Rho=−0.96; P=0.003; n=7: Fig. 1) between side-differences in CV values and the functional scores.

Marked differences in CV values estimated for the healthy and paretic limbs were associated with highly impaired, biceps brachii function. Conversely, patients with either preserved or recovered motor function exhibited similar CV values for both limbs. Whether these side-differences in CV may be explained by structural adaptations remains an open issue. Current results reveal however the CV values may constitute a relevant index to assess the degree of motor function in biceps brachii motor units.