Peak Quadriceps Muscle Torque and Electromyographic Output in Patients With Chronic Respiratory Disorders: Effects of Pulmonary Rehabilitation

OBJECTIVE: To assess the change in relation of the peak quadriceps electromyographic signal to the peak torque produced during a train of 5 isokinetic knee extensions (from 90 degrees below horizontal at a constant speed of 60 degrees/s) at baseline, and at 4 and 8 weeks of pulmonary rehabilitation. DESIGN: In this prospective observational study, isokinetic contractions were recorded during the extensions from the knee bent at 90 degrees to the horizontal plane against graded resistance. Peak quadriceps torque signal (Tq) and peak electromyographic signal (Eq) were recorded by dynamometry and surface electrodes placed at designated locations over the muscle group, respectively. SETTING: Physical therapy department in a tertiary care medical center. PARTICIPANTS: Eighteen patients (9 restrictive lung disease, 6 chronic airflow limitation, 3 non-ILD restrictive; N=18) were compared with 11 healthy control subjects. INTERVENTIONS: Patients underwent an 8-week pulmonary rehabilitation program. MAIN OUTCOME MEASURES: Comparisons of Tq, Eq, and Tq/Eq ratio among patients and controls were by analysis of variance. Associations between physiological variables were determined by multivariable Pearson's correlation. RESULTS: Compared with patients, controls exhibited a 22% higher baseline mean peak Eq (P<.05) and 76% higher mean peak Tq (P=.02) during knee extensions. Patients’ peak Eq/Tq was twice as high as in the controls (P=.02); at 4 weeks, Eq/Tq in patients decreased by 44% (P<.04) with no further decline at 8 weeks; changes in Eq/Tq of 5 of 6 patients paralleled changes in their respective St George's Respiratory Questionnaire scores. There was no change in Tq or Eq/Tq over time among the control cohort. CONCLUSIONS: Eight weeks of pulmonary rehabilitation result in a decrease in Eq/Tq, indicating improvement in force generation of limb muscles, with the change occurring in the first 4 weeks.