FIBER SIZE, ATROPHY, AND HYPERTROPHY FACTORS IN VASTUS LATERALIS MUSCLE FROM 18-YEAR-OLD TO 29-YEAR-OLD MEN

In order to study the size of muscle fibres, cross-sections of autopsi ed vastus lateralis muscle from 8 healthy men, aged 18 to 29 years, wh o have died suddenly were prepared and analyzed. Data were obtained on cross-sectional area, on lesser diameter, and on atrophy and hypertro phy factors of type 1 and type 2 fibres, subdivided into 2a, 2b, and 2 9 fibres. The difference in mean fibre size between type 1 and 2 fibre s was not significant, whereas the differences between type 1 and 2b, type 1 and 2a, and type 2a and 2b fibres were significant. In the whol e material type 2a fibres were the largest and type 2b fibres the smal lest. There were considerable differences between post-mortem subjects . Because of these differences and the variability of all fibre types in respect of size in a sample the normal ranges of fibre size were la rge. The normal ranges and a continuous scale of weights were used to determine the atrophy and hypertrophy factors in each sample, and the upper limits of these factors accepted as being normal. The estimates of the limits of normality of the area, diameter, atrophy and hypertro phy factors of type 1, 2, 2a and 2b fibres reflect the situation in th e vastus lateralis muscle of healthy young men. These values might be useful in studying physiological and pathological conditions influenci ng the size of different fibre types.