Muscle fiber-type distribution predicts weight gain and unfavorable left ventricular geometry: A 19 year follow-up study

Abstract

Background: Skeletal muscle consists of type-1 (slow-twitch) and type-11 (fast-twitch) fibers, with proportions highly variable between individuals and mostly determined by genetic factors. Cross-sectional studies have associated low percentage of type-1 fibers (type-1%) with many cardiovascular risk factors. Methods: We investigated whether baseline type-1% predicts left ventricular (LV) structure and function at 19-year follow-up, and if so, which are the strongest mediating factors. At baseline in 1984 muscle fiber-type distribution (by actomyosin ATPase staining) was studied in 63 healthy men (aged 32-58 years). The follow-up in 2003 included echocardiography, measurement of obesity related variables, physical activity and blood pressure. Results: In the 40 men not using cardiovascular drugs at follow-up, low type-1% predicted higher heart rate, blood pressure, and LV fractional shortening suggesting increased sympathetic tone. Low type-1% predicted smaller LV chamber diameters (P ≤ 0.009) and greater relative wall thickness (P = 0.034) without increase in LV mass (concentric remodeling). This was explained by the association of type-1% with obesity related variables. Type-1% was an independent predictor of follow-up body fat percentage, waist/hip ratio, weight gain in adulthood, and physical activity (in all P ≤ 0.001). After including these risk factors in the regression models, weight gain was the strongest predictor of LV geometry explaining 64% of the variation in LV end-diastolic diameter, 72% in endsystolic diameter, and 53% in relative wall thickness. Conclusion: Low type-1% predicts obesity and weight gain especially in the mid-abdomen, and consequently unfavourable LV geometry indicating increased cardiovascular risk. © 2006 Karjalainen et al; licensee BioMed Central Ltd.