Muscle Fiber Hypertrophy vs. Hyperplasia

[tiramisu]

pubmed is a lot more fun than most forums.

[O-Train]

Contrasts in muscle and myofibers of elite male and female bodybuilders
S. E. Alway, W. H. Grumbt, W. J. Gonyea and J. Stray-Gundersen
Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas.

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.

[O-Train]

pubmed is a lot more fun than most forums.

Yeah. Once you figure out how to set the limits and actually find what you want it's great.

[tiramisu]

Contrasts in muscle and myofibers of elite male and female bodybuilders
S. E. Alway, W. H. Grumbt, W. J. Gonyea and J. Stray-Gundersen
Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas.

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.

The problem I have with this one and similar is it essentially says athletes that have more muscle fibers make more successful bodybuilders. It's just a bit to circular for my taste.

[O-Train]

This is an older but interesting article. I would think rats should be a fairly good model for humans. For some reason when I read this all I can picture is Splinter from TMNT in the gym pumping iron lol.

Skeletal muscle fiber splitting with weight-lifting exercise in rats.
Ho KW, Roy RR, Tweedle CD, Heusner WW, Van Huss WD, Carrow RE.

Adult male albino rats were assigned randomly to control (CON) and weight-lifting (WL) groups. The WL rats were subjected to a progressive weight-lifting program against high resistance for 8 weeks. During the last 2 weeks, each WL rat lifted a load equal to 130% of its body weight. The mean weight of the adductor longus muscle was significantly increased in the WL group ( p < 0.05). This increased muscle weight was shown to be due to an increase in the number of fibers per unit cross-sectional area ( p < 0.05), and the mean sizes of both fast-twitch oxidative glycolytic and slow-twitch oxidative fibers were significantly smaller in the WL rats than in the CON rats (p < 0.05). Light and electron microscopic examination showed that five out of eight WL rats exhibited longitudinally split muscle fibers, while only one CON rat had a few centrally placed nuclei. The splitting process appeared as either a "pinching-off" of a small segment from the parent fiber or an invagination of the sarcolemma deep into the muscle fiber in a plane parallel to the sarcomeres. There were preliminary indications that this work-induced fiber-splitting process may be a physiological adaptation of muscle to the stress of exercise.

[O-Train]

The problem I have with this one and similar is it essentially says athletes that have more muscle fibers make more successful bodybuilders. It's just a bit to circular for my taste.

I know what you mean and they mention that as a shortcoming. I just find it weird that the larger male bodybuilders had more small type II fibers. If only muscle fiber hypertrophy is taking place than why all the smaller type II fibers?