Decreased knee extensor torque and power production in human heart failure

Abstract

Exercise intolerance is a hallmark symptom of chronic heart failure. The goal of this study was to determine if heart failure impairs skeletal muscle torque, power production or contractile velocity. Heart failure patients (n=11; 70.4 ± 4.3 yrs) and controls (n=11; 70.3 ± 3.4 yrs) matched for age, sex and medications that may affect muscle function were evaluated for knee extensor contractile performance, body composition and physical activity level. Groups did not differ in total or regional body composition or physical activity level. Despite similarities in muscle size and use, heart failure patients were characterized by 21‐29% lower (P<0.05 to P<0.01) isometric knee extensor torque throughout a range of knee angles, 15‐33% lower (P=0.05 to P<0.01) peak torque and power output at various isokinetic speeds. These differences in muscle function were evident after adjustment of data for muscle mass. Expression of peak isokinetic torque data relative to isometric torque eliminated group differences, suggesting that impaired function under dynamic conditions is explained by deficits in the force generating capacity of muscle. No group differences were found in the time required to reach target velocity during isokinetic contractions, a proxy of contractile velocity. These results suggest that heart failure reduces skeletal muscle peak torque and power production, but does not alter contractile velocity.