Neuromuscular function : comparison of symptomatic and asymptomatic polio subjects to control subjects

The purpose of this study was to determine if there were any differences between symptomatic and asymptomatic polio survivors by history of acute poliomyelitis illness, electromyographic evidence of terminal motor unit reorganization, and neuromuscular function of the quadriceps femoris muscle. Thirty-four symptomatic postpolio subjects, 16 asymptomatic postpolio subjects, and 41 controls were studied. A questionnaire assessed polio history. Peak knee extension torque was measured isokinetically and isometrically. Endurance (time to exhaustion) was measured at 40% of maximal isometric torque. Work capacity was determined as the product of torque and duration. Recovery of isometric strength was measured at regular intervals for ten minutes after exhaustion. Quantitative electromyography was also performed on the quadriceps to determine motor unit action potential duration and amplitude. It was found that symptomatic subjects had evidence of more severe original polio involvement by history (documented electromyographically), were weaker and capable of performing less work than asymptomatic subjects, and recovered strength less readily than controls.