The postpolio syndrome. An overuse phenomenon.

Persons with good recovery of function following their initial poliomyelitis are now, more than 30 years later, experiencing new weakness, fatigue, and muscle pain. The likelihood of muscle overuse being the cause of this late functional loss was investigated by dynamic electromyography (EMG) and foot-switch stride analysis in 34 symptomatic patients. Manual testing grouped the muscles, with strong (S) encompassing Grades Good (G) and Normal (N) while weak (W) included Fair plus (F+) to zero (0). After testing quadriceps and calf strength, the patients fell into one of four classes: strong quadriceps and calf (SQ/SC), strong quadriceps and weak calf (SQ/WC), weak quadriceps and strong calf (WQ/SC), or combined weak quadriceps and calf (WQ/WC). Quantified EMG (normalized by the manual muscle test EMG) defined the mean duration and intensity of the quadriceps, soleus, lower gluteus maximus, and long head of the biceps femoris during walking. Overuse was defined as values greater than the laboratory normal (mean + 1 SD). Each muscle exhibited instances of overuse, normalcy, and sparing. The biceps femoris was the only muscle with dominant overuse (82%). Quadriceps overuse was next in frequency (53%). Soleus activity infrequently exceeded normal function (34%), but this still represented more than twice the intensity and duration of the other muscles. Gluteus maximus action was also seldom excessive (34%). The patients averaged two muscles with excessive use during walking. Gait velocity of the SQ/SC strong group was highest (71% of normal) while the three categories that included weak muscles had walking speeds in the range of 50% of normal. The finding of muscle overuse during a single free-speed walking test that does not attain normal velocity supports the concept of muscle overuse being the cause of the patient's dysfunction.