The needle biopsy technique for fibre type determination in human skeletal muscle--a methodological study

The fibre type composition (type I, IIA and IIB) was determined in repeated needle biopsies from the vastus lateralis muscle of 34 healthy male subjects. Repeated biopsies were taken from one leg (n = 20), and from both legs (n = 14). The variation between duplicate biopsies was 6.2% and 12.3%, with regard to % type I-fibres, respectively. Corresponding variation in % type IIA-fibres was 4.4% and 7.3%, respectively, and in % type IIB-fibres 5.0% and 7.4%, respectively. The variation in fibre type distribution within a single biopsy was 2.2-3.0% when 200 fibres were classified and counted. Increasing the number of fibres did not reduce the calculated variation to any great extent. A major reduction of the methodological error is obtained when two biopsies are taken from the same site of the muscle. The error in the technique in classifying the type I-fibres was slight; the classification between the subgroups of type II-fibres was, however, to some extent subjected to personal estimate. There was no consistent difference in fibre type composition between the right and the left leg.