NEW YORK (Reuters Health) – Isolated quadriceps training improves muscle structure and oxygen utilization in patients with chronic heart failure, thereby improving exercise tolerance, an Italian team reports in the Journal of the American College of Cardiology for September 20.
Their findings, the authors conclude, provide support for “the efficacy of local skeletal muscle training as a powerful approach to decrease exercise intolerance in patients with CHF.”
Dr. Fabio Esposito, at the University of Milan, and colleagues explain that whole-body exercise increases exercise capacity in patients with CHF, but it is unclear whether this is due to changes in central cardiorespiratory factors or peripheral muscle parameters or both. Several studies, they continue, have shown that small muscle-mass training, which has little effect on central hemodynamics, can improve whole-body exercise capacity in such patients.
To elucidate the mechanisms responsible for this benefit, the team studied muscle structure and oxygen metabolism in six men with CHF and six similar healthy controls before and after 8 weeks of knee-extensor exercise training.
At baseline, peak oxygen uptake during maximal cycle (whole-body) exercise was approximately 17% lower in the CHF group than the controls. Similarly, peak leg oxygen uptake during knee-extensor exercise was about 15% lower in the CHF patients.
The knee-extensor training program did not change cardiac output, as expected, but at the end of the program peak leg oxygen uptake had increased by 53% in the CHF patients, the researchers found, “to a level exceeding that of the untrained controls.”
This was attributable to increases in oxygen delivery, arterial-venous oxygen difference and muscle oxygen diffusion. Structurally, knee-extensor training increased the capillarity of the quadriceps by 21% and mitochondrial density by 25%, the report indicates.
Furthermore, peak oxygen uptake during maximal cycle exercise increased by about 40% after training in the CHF group, matching the controls, Dr. Esposito and colleagues report.
Summing up, they conclude, “These peripheral structural and O2 transport improvements, without a change in cardiac output, provides evidence of significant peripheral vascular and metabolic plasticity in this population that can be developed in isolation with small muscle mass training and then harnessed to the benefit of whole-body exercise capacity.”
They add, “These mechanistic findings may have important practical consequences in terms of guiding future pharmacological and rehabilitative interventions in this population.”
Isolated Quadriceps Training Increases Maximal Exercise Capacity in Chronic Heart Failure: The Role of Skeletal Muscle Convective and Diffusive Oxygen Transport
J Am Coll Cardiol 2011;58:1353-1362.