Representativeness of a muscle biopsy specimen for the whole muscle.

To investigate whether the muscle fibre area and the proportion of fibre types in a biopsy specimen are representative of the muscle, seven specimens from the anterior tibial muscle were compared with seven necropsy specimens including the whole cross-sectioned anterior tibial muscle. The fibre area of the transverse section differed greatly between biopsy and necropsy specimens, and also between different regions of the necropsy specimens, probably owing to different degrees of muscle fibre contraction. Relative measures, the coefficient of variance for the mean fibre area and the differences in size between type I and type II fibres, proved to be reliable. The proportion of fibre types varied greatly between adjacent fascicles and in different regions of the necropsy specimens. The mean proportion of type II fibres can vary from 7-30% in two biopsies from the same muscle. Great caution is therefore recommended when the proportion of fibre types in a biopsy specimen is assumed to be valid for the proportion of fibre types in the whole muscle: specimens must be taken from several sites.