Female-related skeletal muscle phenotype in patients with moderate chronic heart failure before and after dynamic...

This study hypothesized that female patients with chronic heart failure (CHF), similarly as previously reported for male patients, have a decreased proportion of type I (slow twitch) muscle fibers combined with fiber atrophy, and respond to exercise training with an increased muscular fiber area and performance, and with an unaltered fiber type distribution.

Sixteen women [age 62 +/- 10 years (mean +/- SD)] with stable, moderate CHF (left ventricular ejection fraction 28 +/- 8%) underwent percutaneous needle biopsies of the lateral vastus muscle, and assessments of isokinetic muscle strength and exercise tests with respiratory gas and blood lactate analyses, before and after 8 weeks of intensive knee extensor endurance training.

When compared to healthy age-matched women, the women with CHF unexpectedly had a normal proportion of type I fibers (51 +/- 15%), but a decreased cross-sectional area in both type I and II fibers. Exercise training increased the cross-sectional area of muscle fibers up to the reference range (21%, p < 0.04), while the relative number of type I fibers decreased (12%, p < 0.03). Training also increased muscle strength (16%, p < 0.0001) and peak oxygen uptake (20%, p < 0.0001). The increase in peak oxygen uptake was directly related to the training-induced increase in fiber areas (r = 0.63; p < 0.03), and decrease in lactate accumulation was inversely related to the training-induced decrease in the relative number of type I fibers (r = -0.62; p < 0.02).

As for men with CHF, a skeletal muscle atrophy was found in women, but contrary to the hypothesis, the proportion of type I muscle fibers was normal. Exercise training counteracted the atrophy suggesting skeletal muscle trainability in female CHF patients.