Muscle performance, voluntary activation and perceived effort in normal subjects and patients with prior...

Many people previously affected by polio complain of increased fatigue, weakness and pain many years after the initial illness. Although electromyographic abnormalities have been found in these patients, the cause of their increased weakness is not well understood. Previous studies have shown decreased strength and impaired exercise performance in those with prior polio, but the level of voluntary drive to the muscle has not been investigated. The present study investigated maximal voluntary activation without fatigue and both peripheral and central components of muscle fatigue during exercise in 21 subjects with poliomyelitis 20-40 years previously, and 20 healthy, age-matched control subjects. Voluntary activation and strength of the elbow flexors were quantified using twitch interpolation during maximal isometric voluntary contractions both at rest, and during fatigue induced by 45 min of repeated isometric contractions. Compared with the control subjects, patients with prior polio had impaired voluntary activation both when the elbow flexors were not fatigued and during fatiguing submaximal exercise. During exercise, polio subjects also had lower twitch amplitudes and increased subjective fatigue. Central and peripheral fatigue were more marked in those with the post-polio syndrome. The impaired voluntary activation with unfatigued muscles in polio subjects indicates that defective central or reflex drive may contribute to their new weakness.