Intermittent isometric activity: its effect on muscle fatigue in postpolio subjects

Symptomatic postpolio patients report improved function when they pace their activities, but this has never been objectively assessed. The purpose of this study was to determine whether seven symptomatic postpolio subjects would (1) have less evidence of local muscle fatigue and recover strength more readily when they pace their activity (via work-rest intervals) than when they work at a constant rate to exhaustion, and (2) be able to perform more work with less fatigue by pacing. Subjects were evaluated on three separate days with at least one week between tests. On the first test day (constant exercise), isometric peak torque (MVC) of the quadriceps was determined and an isometric endurance test was performed to exhaustion at 40% of MVC. Thirty seconds after exhaustion the subject performed an MVC. One psychophysiologic and two electrophysiologic variables associated with fatigue were measured during the testing procedure. Work capacity (TTI) was determined as torque x time. In test 2 (quartile exercise), the same TTI was performed at 40% of MVC, but in this instance the work was performed in quartiles with two-minute rest breaks between work quartiles rather than continuously to exhaustion. In test 3 (interval exercise), exercise was performed at 40% of MVC in 20-second bouts with two-minute rest breaks until rating of perceived exertion exceeded 17 (very hard), or until six-minutes of work were performed. Analyses demonstrated that both work-rest interval programs resulted in less evidence of local muscle fatigue, increased capacity to perform work, and increased ability to recover strength after activity in symptomatic postpolio patients.