Changes in muscle morphology, strength and enzymes in a 4-5-year follow-up of subjects with poliomyelitis sequelae.

Twenty subjects with polio sequelae were studied on two occasions 4-5 years apart by means of dynamometer measurements of knee-extension and flexion strength and muscle biopsy for histochemical and enzymatic analyses. The subjects were divided into those who reported (unstable, n = 12) and did not report (stable, n = 8) new or increased muscle weakness in the tested leg between the two examinations. Muscle strength decreased significantly in the unstable subjects, but only for knee-flexion in the stable subjects. However, the endurance test comprising 50 consecutive knee-extensions at 180 degrees/sec showed increased fatigability at the second examination only in the stable subjects. Most subjects had markedly increased muscle fiber areas, which in some subjects increased further, but in those already with very extreme hypertrophy the fiber size decreased. Capillarization and activity of citrate-synthase were decreased at the initial examination, but no significant further reduction was observed at the second examination. The results demonstrate individual patterns in the compensatory process for the presumed loss of motor units.