Muscle Fiber Types

Muscle Fiber Types

While all motor units behave in the same way, this cannot be said for all muscle fibers. Not all muscle fibers have the same biochemical (metabolic) functions. Every muscle fiber can function under both anaerobic and aerobic conditions, although some muscle fiber work better under anaerobic conditions, while others muscle fiber work better under aerobic conditions.

The muscle fibers that rely on and use oxygen to produce energy are aerobic, type I, red, or slow-twitch (ST) fibers. The muscle fibers that do not require oxygen are anaerobic, type II, white, or fast-twitch (FT) muscle fibers. Low-twitch (ST) and fast-twitch (FT) fibers exist in relatively equal proportions within the body, and this 50/50 relationship is not thought to be greatly affected by strength training and bodybuilding.

The recruitment of muscle fibers is load-dependent. During moderate and low intensity activity, slow-twitch (ST) fibers are recruited as work horses. As the load increases, a greater number of FY fibers are activated during a contraction.

The distribution of muscle fiber types can vary, both within the same muscle and among different muscle. Usually, the arms tend to have a higher percentage of fast-twitch (FT) fibers than the legs: biceps 55% fast-twitch (FT), triceps 60% fast-twitch (FT), whereas soleus (calves) 24% fast-twitch (FT) muscle fiber.

Fiber type composition (i.e. proportion of fast-twitch (FT)T fibers within a muscle) plays an important role in strength training and bodybuilding. Muscles containing a high percentage of fast-twitch (FT) fibers are capable of quicker and more powerful contractions.

There are no clear differences in muscle fiber distribution between female and male athletes. An inherited propensity toward more fast-twitch (FT) muscle fibers might indicate which individuals are genetically suited to strength training and bodybuilding. While genetics is an important factor in determining success, it is not the only one. Regardless of one's genetic endowments, every individual, through intensive training and proper nutrition, can improve his or her muscle size, tone and definition.

Subscribe to our Newsletter

FREE Bodybuilding Tips and Advice



Get your Bodybuilding Supplements at discounted price

Know More About Your Body

Copyright 101 BodyBuilding All rights Reserved. Sitemap

All Trademarks are the property of their respective owners.

Contact Us | Terms of Use | Privacy Policy