Muscle fibre area, fibre type & capillarization in male and female body builders.

The effects of long-term strength training on skeletal muscle fibre characteristics were evaluated in nine body builders (BB) (five males and four females) and ten control subjects (six females and four males). Muscle fibre area, percentage fibre type, and capillary supply were compared between the BB and controls as well as between the males and females with a two-way analysis of variance design. For the fast-twitch fibre area (FTa), the BB had larger areas than the controls, and males had larger areas than females. The analysis for the slow-twitch fibre areas (STa) showed only a training effect; BB had a larger STa than controls. The FTa in the untrained females and the female BB were similar to their STa; in contrast, both male groups had significantly larger FTa than STa. The BB had significantly more capillaries per fibre than the control groups but the number of capillaries/mm2 were similar in all groups. The results suggest that prolonged training in the female BB hypertrophies both the FT and ST fibres. The female BB realized the same increase in capillary per fibre ratio (#cap/f) as the male BB. However, the larger area of the FT fibres compared to the ST fibre seen in both male groups was not observed in either female group.