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

Abstract

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 (VO 2peak ), measured during cycle ergometry (blacks: 42·6 ± 4, whites: 44·3 ± 4 ml·kg -1 ·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.