Importance of total leg muscle mass for exercise intolerance in chronic heart failure

Patients with chronic heart failure symptoms tend to avoid voluntary effort and are thus subject to physical deconditioning. The presence of symptoms in daily life is thought to predispose to physical deconditioning and subsequent skeletal muscle loss. This study was designed to describe the relation among daily physical activities, skeletal muscle loss and exercise capacity in patients with chronic heart failure. We studied 14 patients with severe cardiac dysfunction (left ventricular ejection fraction < 40%) and 7 age-matched normal subjects. We measured total leg muscle mass by dual energy X-ray absorptiometry. The patients were divided into 7 asymptomatic and 7 symptomatic individuals using questionnaires for specific physical activities. Peak oxygen uptake and anaerobic threshold were significantly reduced in cardiac patients as compared with normal subjects. The reduction in exercise capacity was greater in the symptomatic patients than in asymptomatic patients. Leg muscle mass was significantly reduced (-17%) in the symptomatic patients, while it remained normal in the asymptomatic patients. Oxygen uptake in unit muscle mass at the level of anaerobic threshold and at peak exercise was decreased in both the asymptomatic (-21% and -21%, respectively) and symptomatic patients (-27% and -30%, respectively) but the difference between these two groups was not significant. In the asymptomatic patients, the reduced exercise capacity was accounted for primarily by muscle mass-independent factors such as an impaired nutritive blood flow to exercising muscles or metabolic abnormalities within the muscle cell. In the symptomatic patients, the marked reduction in exercise tolerance was attributable to a decrease in leg muscle mass and to hemodynamic or metabolic abnormalities. We conclude that the loss of leg muscle mass plays an important role in exercise intolerance in patients who are prone to physical deconditioning as a result of symptomatic heart failure.