Electromyographic and neuromuscular variables in post-polio subjects.

OBJECTIVE

Post-polio subjects experience functional deterioration many years after developing acute poliomyelitis and have been shown previously 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 electromyography (EMG) and correlated these variables with isometric strength, endurance, "work capacity," and strength recovery after fatiguing isometric exercise.

DESIGN

A cohort of 12 post-polio subjects was tested for neuromuscular function. Electromyographic variables were determined on a separate day.

SETTING

Volunteers were recruited from the community and tested in our neuromuscular research laboratory.

SUBJECTS

A volunteer sample was obtained from advertisements. All subjects acknowledged post-polio syndrome symptoms.

MAIN OUTCOME MEASURES

Neuromuscular variables were isometric knee extension peak torque, endurance (time to exhaustion) at 40% of maximal torque, tension time index, and recovery of torque at 10 minutes. Electromyographic variables were macro EMG and single fiber EMG (percent blocking and jitter).

RESULTS

Macro EMG amplitude was ninefold the control value, and both jitter and blocking were greatly increased in comparison to control values. Isometric strength significantly (p < .05) correlated negatively with macro EMG amplitude.

CONCLUSIONS

The weakest subjects had the greatest number of muscle fibers within the motor unit (as measured by macro EMG amplitude). Jitter and blocking did not correlate with neuromuscular function.