Skeletal muscle fibre type and capillary density in college-aged blacks and whites

The purpose of this study was to compare muscle fibre type proportions and capillary density in untrained, college-aged blacks (n = 14) and whites (n = 14). Both groups were similar in terms of peak oxygen uptake (VO2peak), measured during cycle ergometry (blacks: 42.6+/-4, whites: 44.3+/-4ml.kg.min(-1)mean+/-SD). Muscle samples were obtained from the quadriceps femoris (vastus lateralis) by the needle biopsy technique. Fibre type was determined by myosin ATPase stain (pH = 4.54) and capillaries were identified by amylase-periodic acid Schiff (PAS) stain. The percentage of type I, IIa, and IIb fibres in the blacks was 39.5+/-11.5, 40.0+/-8.4, and 22.8+/-9.8, respectively. In whites the percentage of type I, IIa, and IIb fibres was 44.9+/-8.5, 36.6+/-6.9, and 18.3+/-9.6, respectively. No significant differences were noted between the two racial groups for type I, IIa, or IIb fibres. Capillary density was 277+/-39/mm(2) in the blacks compared to 289+/-32/mm(2) in the whites. Capillary density was positively correlated to percentage of type I fibres (r = 0.497) and negatively correlated to percentage of type IIa fibres (r = -0.389), in the overall study population. These data suggest that if racial differences in fibre type do exist, such differences are small compared to the variability in this measure.