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

Cross-sectional muscle fibre areas (type I, IIA and IIB) 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 μm² for type I, 1020 μm² for type II A and 860 μm² 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, IIA and IIB 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.