Quantitative measurement of muscle fiber composition in a normal population

To obtain normative muscle morphology data on a healthy population recruited from a population survey, we examined vastus lateralis biopsies from 58 men and 33 women, aged 26-67 years. Biopsies were measured with automated, computer-aided techniques. Data were analyzed according to gender and age, and the influence of blood pressure, body mass index (BMI), and smoking habits was also examined. Men had larger muscle fibers (fiber area similar to5,400 mum(2)) than women (similar to4,000 mum(2), P = 0.003). No gender differences were seen in fiber composition, fiber roundness, percentage of connective tissue, or capillary density. Blood pressure did not influence fiber size or composition, but was correlated with fiber roundness in men. BMI was associated with fiber area in men, but not in women. Variations in age, smoking habits, and physical activity did not influence muscle morphology data substantially. Thus, in a normal population, men have larger muscle fibers than women, but similar fiber composition. Variation in gender, BMI, blood pressure, and physical activity may influence morphological features to a minor degree.