Contrasts in muscle and myofibers of elite male and female bodybuilders

Abstract

Muscle cross-sectional area (CSA), fiber area, and fiber number were determined from the biceps brachii of eight elite male bodybuilders (MB) and five elite female bodybuilders (FB) who had similar training characteristics. Biceps CSA was obtained from computer tomographic scanning and corrected for noncontractile tissue. Biceps CSA was twofold greater in MB relative to FB and strongly correlated to lean body mass (R = 0.93). Biceps CSA expressed per kilogram lean body mass (LBM) or per centimeter body height (BH) was 35% greater in MB compared with FB. Most of the gender difference in muscle CSA was because of greater absolute mean fiber areas in MB (9,607 microns2) relative to FB (5,386 microns2); however, MB also had a significantly greater population of small type II fibers (less than 2,000 microns2) compared with FB. Type II fiber area/LBM averaged 1.6-fold greater in MB compared with FB; however, type I fiber area/LBM was similar between groups. Biceps CSA was positively correlated to fiber CSA (R = 0.75) and fiber number (R = 0.55). This suggests that adaptations to resistance training may be complex and involve fiber hypertrophy and fiber number (e.g., proliferation). Alternatively, since the muscle characteristics before training are not known, these apparent adaptations might be genetically determined attributes.

Gender differences in strength and muscle fiber characteristics

“…A similar gender difference in fiber size has been reported for the biceps brachii of male and female bodybuilders (Alway et al 1989).…”

“…Other studies which have corrected for connective tissue offer conflicting results. Alway et al (1989) found no significant gender difference in fiber number in the biceps brachii of male and female bodybuilders. In contrast, untrained females were found to have significantly fewer muscle fibers in the biceps brachii (MacDougall et al 1983;Sale et al 1987) and the tibialis anterior (Henriksson-Larsen 1985).…”

“…Other investigators have reported similar fiber type distribution patterns in the tibialis anterior of untrained males and females (Henriksson-Larsen 1985), the biceps brachii of male and female bodybuilders (Alway et al 1989), and the vastus 20 lateralis of untrained males and females (Prince et al 1977). In contrast, Komi and Karlsson (1978) found male vastus lateralis contained a higher percentage of slow-twitch fibers (55.9%) than comparable female muscle tissue (49.1%).…”

“…Alway et al (1989) failed to observe a significant gender difference in fiber number in the biceps brachii of male and female bodybuilders. In studies involving untrained subjects, females were found to have significantly fewer muscle fibers in the biceps brachii (MacDougall et al 1983;Sale et al 1987).…”

“…Studies which have corrected for the amount of connective tissue present in muscle offer conflicting results (MacDougall et al 1983;Sale et al 1987;Alway et al 1989). Alway et al (1989) failed to observe a significant gender difference in fiber number in the biceps brachii of male and female bodybuilders.…”