Muscle Rearrangement in Patients with Hemiparesis after Stroke: An Electrophysiological and Morphological Study

Abstract

Skeletal muscle changes were evaluated in patients suffering from hemiparesis after stroke. Concentric needle EMG and single fiber EMG of the paretic gastrocnemius medialis muscle were performed. Maximal amplitude of H, T and M responses in calf muscles of both the affected and the unaffected sides were determined by usual electrophysiological techniques. Muscle biopsy of the lateral gastrocnemius muscle of the affected side was performed to determine the distribution of fiber types and fiber sizes. Fibrillation activity and positive sharp waves occurred in paretic muscles in patients with more recent hemiparesis while the duration of motor unit potentials was prolonged in patients with long-lasting disease. The H/M ratio was increased on the paretic side. The percentage of type 1 fibers was augmented in most patients with normal mean diameter and low atrophy factor. The percentage of type 2 fibers was reduced with decreased mean diameters and with a high atrophy factor. Such changes may be related to inactivity or transsynaptic degeneration of type 2 motoneurons as a consequence of the interruption of the corticospinal tract. Increased percentage of type 1 fibers may be due to a collateral reinnervation process or a motor unit type transformation.

Effects of velocity on maximal torque production in poststroke hemiparesis

“…However, there were no significant between-limb differences in EMG levels. One possible mechanism that could explain this observation is selective decrease and atrophy of fast-twitch, type II muscle fibers, 14,15,48 , resulting in a higher percentage of type I fibers in the elbow flexors of the paretic limb. A related but alternative explanation is that decreased descending drive to the motoneuron pool of the paretic elbow flexors resulted in the inability to recruit high-threshold, fast-twitch motor units.…”

Factors That Influence Muscle Weakness Following Stroke and Their Clinical Implications: A Critical Review

“…24 The motor units lost tend to be large alpha motor neurons innervating fast-twitch fibres, which are more susceptible to death; the result is a muscle composed predominantly of larger and slower motor units. 25 The reduction in fibre size following stroke may be influenced by disuse or by other age-related processes (see below).…”

Functional recovery and muscle properties after stroke: a preleminary longitudinal study

“…The latter is already reported in the second week after stroke onset (Jorgensen & Jacobsen, 2001). For instance, a change in muscle fiber composition, characterized by selective type II fiber atrophy and predominance of (slow twitch, oxidative) type I fibers has been shown in paretic muscles (Edstrom, 1970;Scelsi et al, 1984;Dietz et al, 1986;Dattola et al, 1993;Hachisuka et al, 1997), which would lead to concomitant changes in contractile speed of the muscle fibers towards those of slow muscles. We can imagine that such a change in fiber type composition can be combated, for instance by training, during the first year after stroke, so that muscle speed characteristics can be restored.…”