SKELETAL-MUSCLE SIZE - RELATIONSHIP TO MUSCLE FUNCTION IN HEART-FAILURE

Abnormalities of skeletal muscle function and metabolism are common in patients with congestive heart failure (CHF) and appear to contribute to systemic exercise limitation. Although the mechanism for these differences is unclear, one possibility is skeletal muscle atrophy. In 21 CHF patients and 12 sex- and age-matched sedentary control subjects, we quantified muscle size as maximal cross-sectional area (MCSA) of thigh muscles measured by magnetic resonance imaging and determined the relationship between muscle size and muscle function. Muscle strength was measured as maximum force developed during isometric contractions, and muscle endurance was quantified as the decline in force during 15 consecutive isokinetic knee extensions (measured as ratio of mean peak torque of last 3 and first 3 extensions). MCSAs of thigh muscles (141 +/- 28 vs. 167 +/- 47 cm2; P < 0.05) and knee extensors (62 +/- 13 vs. 75 +/- 13 cm2; P < 0.05) were both significantly smaller in patients than in control subjects. These differences persisted after normalization for body size. Isometric strength was less, but not significantly so, in patients (126 +/- 39 vs. 135 +/- 43 Nm; P = NS), but muscle endurance was markedly impaired (endurance ratio 0.67 +/- 0.14 vs. 0.83 +/- 0.11; P < 0.05). A strong correlation was found between isometric strength (r = 0.76) and MCSA of knee extensors, but only a weak correlation between dynamic endurance and MCSA was seen. We conclude that muscle size is smaller in CHF patients but that maximal force generated per area of muscle is not impaired. However, smaller muscle size does not fully explain the impairment of endurance, which therefore reflects a qualitative rather than solely a quantitative difference in skeletal muscle in CHF.