Poliomyelitis and the post-polio syndrome: exercise capacities and adaptation--current research, future directions, and widespread applicability.

Poliomyelitis is an acute viral disease that attacks the brain and the ventral horn of the spinal cord. Damage to the lower motor neurons usually results in atrophy and weakness of muscle groups, perhaps paralysis and possibly deformity. A second type, bulbar poliomyelitis, infects the medulla oblongata and may result in dysfunction of the swallowing mechanism along with respiratory and circulatory distress. Minor forms of poliomyelitis result in fever, sore throat, headache, and upper body stiffness, but leave no significant atrophy or paralysis. The purpose of this paper is to review post-polio syndrome (PPS) as well as the effect of exercise on the symptoms and morphologic adaptations to PPS and where future research efforts should be directed. The most common features of PPS for over 350,000 afflicted survivors include general fatigue, weakness, and joint/muscle pain. The primary reasons for these symptoms include 1) destruction of the anterior horn cells by the polio virus, leaving fewer motor neurons to induce muscle contraction; 2) unaffected motor unit enlargement by reinnervation through terminal sprouting; and 3) defective transmission at the neuromuscular junction secondary to failure of terminal axonal sprout. Acute responses to resistive exercise suggest significant muscle strength decrements in the knee extensors compared with similar aged people without polio. However, limited training investigation indicates significant strength increases for the knee extensors following at least 6 wk of training. Acute aerobic responses also differ significantly from those observed in aged-matched control subjects. Chronic aerobic responses to limited training studies suggest significant elevations in maximal oxygen uptake.(ABSTRACT TRUNCATED AT 250 WORDS)