Isolated Quadriceps Training Increases Maximal Exercise Capacity in Chronic Heart Failure The Role of Skeletal Muscle Convective and Diffusive Oxygen Transport

Objectives This study sought to elucidate the mechanisms responsible for the benefits of small muscle mass exercise training in patients with chronic heart failure (CHF). Background How central cardiorespiratory and/or peripheral skeletal muscle factors are altered with small muscle mass training in CHF is unknown. Methods We studied muscle structure, and oxygen (O-2) transport and metabolism at maximal cycle (whole-body) and knee-extensor exercise (KE) (small muscle mass) in 6 healthy controls and 6 patients with CHF who then performed 8 weeks of KE training (both legs, separately) and repeated these assessments. Results Pre-training cycling and KE peak leg O-2 uptake (VO2peak) were similar to 17% and similar to 15% lower, respectively, in the patients compared with controls. Structurally, KE training increased quadriceps muscle capillarity and mitochondrial density by similar to 21% and similar to 25%, respectively. Functionally, despite not altering maximal cardiac output, KE training increased maximal O-2 delivery (similar to 54%), arterial-venous O-2 difference (similar to 10%), and muscle O-2 diffusive conductance (DMO2) (similar to 39%) (assessed during KE), thereby increasing single-leg VO2peak by similar to 53%, to a level exceeding that of the untrained controls. Post-training, during maximal cycling, O-2 delivery (similar to 40%), arterial-venous O-2 difference (similar to 15%), and DMO2 (similar to 52%) all increased, yielding an increase in VO2peak of similar to 40%, matching the controls. Conclusions In the face of continued central limitations, clear improvements in muscle structure, peripheral convective and diffusive O-2 transport, and subsequently, O-2 utilization support the efficacy of local skeletal muscle training as a powerful approach to combat exercise intolerance in CHF. (J Am Coll Cardiol 2011;58:1353-62) (C) 2011 by the American College of Cardiology Foundation