ELECTROMYOGRAPHIC AND NEUROMUSCULAR VARIABLES IN POSTPOLIO SUBJECTS

Objective: Post-polio subjects experience functional deterioration man y years after developing acute poliomyelitis and have been shown previ ously to have a deficit in strength recovery after isometric activity. This study characterized the size and stability of the motor units in a group of post-polio subjects with macro and single fiber electromyo graphy (EMG) and correlated these variables with isometric strength, e ndurance, ''work capacity,'' and strength recovery after fatiguing iso metric exercise. Design: A cohort of 12 post-polio subjects was tested for neuromuscular function. Electromyographic variables were determin ed on a separate day. Setting: Volunteers were recruited from the comm unity and tested in our neuromuscular research laboratory. Subjects: A volunteer sample was obtained from advertisements. All subjects ackno wledged post-polio syndrome symptoms. Main Outcome Measures: Neuromusc ular variables were isometric knee extension peak torque, endurance (t ime to exhaustion) at 40% of maximal torque, tension time index, and r ecovery of torque at 10 minutes, Electromyographic variables were macr o EMG and single fiber EMG (percent blocking and jitter). Results: Mac ro EMG amplitude was ninefold the control value, and both jitter and b locking were greatly increased in comparison to control values. Isomet ric strength significantly (p <.05) correlated negatively with macro E MG amplitude. Conclusions: The weakest subjects had the greatest numbe r of muscle fibers within the motor unit (as measured by macro EMG amp litude). Jitter and blocking did not correlate with neuromuscular func tion. (C) 1995 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation.