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

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Abstract
The fiber 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 1 leg (n = 20), and from both legs (n = 14). The variation between duplicate biopsies was 6.2% and 12.3%, with regard to percent type I-fibers, respectively. Corresponding variation in percent type IIA-fibers was 4.4% and 7.3%, respectively and in percent type IIB-fibers 5.0% and 7.4%, respectively. The variation in fiber type distribution within a single biopsy was 2.2-3.0% when 200 fibers were classified and counted. Increasing the number of fibers did not reduce the calculated variation to any great extent. A major reduction of the methodological error is obtained when 2 biopsies are taken from the same site of the muscle. The error in the technique in classifying the type I-fibers was slight; the classification between the subgroups of type II-fibers was to some extent subjected to personal estimate. There was no consistent difference in fiber type composition between the right and the left leg.