An 8-year longitudinal study of muscle strength, muscle fiber size, and dynamic electromyogram in individuals with late polio

Twenty‐one subjects with polio 24 to 51 years prior to the first examination were studied on three occasions, each 4 years apart with measurements of muscle strength and endurance for knee extension, macro EMG, and muscle biopsy from vastus lateralis. On average the muscle strength decreased during the 8‐year follow‐up by 9–15%. Endurance decreased during the observation period. The muscle fiber area was markedly increased in most subjects. There was a decrease in the capillarization during the follow‐up. Macro EMG was increased in all subjects (range 3–42 times control) and increased in 20 legs during the 8‐year follow‐up, but showed a decrease in 8 of 9 legs with an approximative breakpoint when macro MUPs were around 20 times the normal size. Thus, evidence of on‐going denervation/reinnervation as well as of failing capacity to maintain large motor units was demonstrated. SFEMG showed a moderate degree of disturbed neuromuscular transmission. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21: 1428–1437, 1998