Single Skeletal Muscle Fiber Performance is Altered in Heart Failure Patients

A decrease in whole skeletal muscle performance is common in heart failure patients. We examined the viscoelastic properties of individual human skeletal muscle fibers using small amplitude sinusoidal analysis to test the hypothesis that heart failure affects skeletal muscle mechanics and kinetics at the single fiber level. We obtained vastus lateralis (quadriceps) muscle from needle biopsies of 7 heart failure patients and 4 sedentary controls. At low [Ca2+] (pCa 8, 25°C), Type I (slow contraction velocity) and Type IIA (fast contraction velocity) muscle fibers from heart failure patients had lower isometric tensions as well as lower elastic and viscous moduli. Notably, Type I and IIA fibers produce positive oscillatory work and power at pCa 8. Type I fibers from heart failure patients at low [Ca2+] produced less oscillatory work and had a higher frequency of maximum work, indicating an increase in myosin kinetics, compared to controls. At high [Ca2+] (pCa 4.5, 25°C), Type I and IIA fibers from heart failure patients showed similar isometric tensions and myosin kinetics parameters as controls. In contrast to low [Ca2+], at high [Ca2+] Type I and IIA fibers from heart failure patients had a larger elastic modulus at low oscillation frequencies and consistently produced greater oscillatory work and power than control fibers. Together, these results indicate that heart failure modifies single skeletal muscle fiber performance at the level of the myosin-actin cross-bridge, although the effect differs between low and high [Ca2+]. The relevance of these differences to reduced whole muscle function in heart failure patients awaits further studies.