Myoelectric manifestations of muscle changes in stroke patients

Objective: To evaluate the development of myoelectric fatigue in paretic and healthy tibialis anterior muscles of stroke patients. Design: Case series. Setting: Occupational therapy and clinical neurophysiology unit. Participants: Eight patients with hemiparesis or hemiplegia 9 months to 10 years poststroke. Main Outcome Measures: Current pulses of 0.1-ms width and 40-Hz repetition rate were applied for 10 seconds with a monopolar technique; myoelectric signals (M waves) were detected with surface electrodes. Results: Mean values and initial values of the median frequency (MDF) between paretic and healthy side were statistically different, with the values on the healthy side much higher than the paretic side. Changes of MDF showed a decreasing pattern for both the paretic and the healthy sides, with the downslope of the curve of the healthy side more evident. Conclusions: In paretic muscles of stroke patients, the tendency toward atrophy of type II fibers appears to be frequent. Our study suggests this muscle rearrangement uses techniques much less invasive than muscle biopsy, and gives useful information about muscle function. This kind of information can help identify rehabilitation strategies, particularly for chronic stroke survivors.