How to calculate human muscle fibre areas in biopsy samples--methodological considerations

Cross-sectional muscle fibre areas (type I, II A and II B) were determined in duplicate biopsies from the left vastus lateralis (n = 11) and in biopsies from right and left vastus lateralis (n = 8). The SD for the difference in means between duplicate biopsies was 510 microns 2 for type I, 1020 microns 2 for type II A and 860 microns 2 for type II B. Expressed as coefficient of variation (CV) these SD constituted 10, 15 and 15%, respectively. The variation in fibre size within a sample was considerably less than the variation between samples on the assumption that at least 15-20 areas of each fibre type were measured per sample. No difference in mean fibre area for type I, II A and II B fibres was obtained between the right and left muscle. Several artefacts due to the sampling and preparing procedures are discussed and a method for determining muscle fibre areas in biopsy samples is suggested.