ELECTROMYOGRAPHIC AND NEUROMUSCULAR VARIABLES IN UNSTABLE POSTPOLIO SUBJECTS, STABLE POSTPOLIO SUBJECTS, AND CONTROL SUBJECTS

Objective: To compare strength and endurance variables obtained in the quadriceps muscles of postpolio and control subjects over a 7-year in terval with macro and single fiber electromyography (EMG) variables. D esign: A controlled inception cohort study. Setting: Neuromuscular res earch laboratory of a university hospital. Subjects: A cohort of 23 po stpolio and 14 control subjects. All postpolio subjects had a history, physical examination, and EMG consistent with previous poliomyelitis, and had greater than antigravity strength in the quadriceps muscle te sted. Unstable postpolio subjects acknowledged new quadriceps weakness over the 7-year period of the study (n = 11), and stable postpolio su bjects denied new weakness of the quadriceps over the same period (n = 12). Main Outcome Measures: All subjects had tests of neuromuscular f unction of the quadriceps muscles at the onset of this study and yearl y over a 7-year period. EMG variables were determined on a separate da y after the seventh year of neuromuscular measurements. Neuromuscular variables measured were isometric knee extension peak torque, isometri c endurance (time to inability to maintain knee extensor contraction a t 40% of maximal torque), tension time index (TTI) (product of isometr ic endurance time and 40% of maximal torque), and recovery of torque a t 10 minutes after the endurance test. EMG variables were macro EMG an d single fiber EMG (jitter, fiber density, and percent blocking). Resu lts and Conclusions: Unstable postpolio subjects did not lose strength more rapidly than stable postpolio subjects or control subjects. Unst able postpolio subjects were significantly weaker, had decreased TTI, larger macro EMG amplitude, greater jitter, blocking, and fiber densit y in comparison with stable postpolio subjects (all p < .05). Strength was negatively correlated with macro EMG amplitude in the stable post polio group (p < .05). The slope of the regression line of strength ov er 7 years did not correlate (p > .05) with neuromuscular or EMG varia bles in control, stable, or unstable postpolio subjects. (C) 1997 by t he American Congress of Rehabilitation Medicine and the American Acade my of Physical Medicine and Rehabilitation.