Relationship of skeletal muscle fiber type to serum high density lipoprotein cholesterol and apolipoprotein A-I levels

We measured the percentage of slow-twitch(ST) muscle fibers in the lateral portion of the quadriceps femoris muscle in 41 healthy sedentary male controls, 35 active male joggers, and 26 male coronary heart disease (CHD) patients. We then compared these percentages with serum levels of total cholesterol (TC), triglycerides (TG), high density lipoprotein cholesterol (HDL-C) and apolipoprotein A-I (apo A-I) found in these 102 middle-aged men. The percentage of ST muscle fibers in all men correlated positively with serum HDL-C (r = 0.57, P < 0.001) and with apo A-I (r = 0.60, P < 0.001) and negatively with triglycerides (r = −0.43, P < 0.001). The proportion of ST fibers in joggers (65%; 61–69%, 95% confidence interval) was higher (P < 0.001) than in sedentary controls (48%; 44–52%) or in CHD patients (44%; 39–49%). Moreover, 89% of the joggers had a proportion of ST fibers higher than 50%, whilst in sedentary controls and in CHD patients these values were 46% and 38%, respectively. Positive correlations were found between the percentage of ST fibers and both HDL-C and apo A-I in controls (r = 0.33, P < 0.05andr = 0.34, P < 0.05) and in joggers (r = 0.46, P < 0.01,andr = 0.40, P < 0.05), respectively. Negative correlations in controls (r = − 0.34, P < 0.05) and in CHD patients (r = − 0.43, P < 0.05) were also found between the percentage of ST fibers and serum TG. Taking into account in the regression model age, body mass index, smoking, alcohol consumption and group, the percentage of ST fibers significantly contributed to serum HDL-C (P < 0.05) and serum apo A-I (P < 0.01) levels. The association between the percentage of ST fibers and serum HDL-C levels may be due to the fact that muscles with a high percentage of ST fibers have a high capacity to use fatty acids liberated from trig;yceride-rich lipoproteins, which elevates serum HDL-C levels. The muscle fiber distribution mayl also be a constitutional factor which increases the likehood that a person involved in endurance training, which further increases serum HDL-concentration.