Gettin’ Twitchy With It
A little A&P review for CFers today! Muscles are composed of bundles of fibers called myocytes. These bundles are categorized into three separate types:
- Type I fibers = slow twitch, use oxygen for energy (aerobic) and are responsible for providing contractions over a long period of time (think marathons)
- Type IIA fibers = half way between Type I and Type IIB, equal parts aerobic and anaerobic
- Type IIB fibers = fast twitch, anaerobic, used for quick energy and speed like sprinting or weight lifting
People are born with certain proportions of each type of fiber, which is different for each individual but averages about 50/50. Naturally having more of one fiber type doesn’t mean you’re destined to be a sprinter or marathon runner, though. Some research suggests that training can at least slightly alter your muscle fiber composition.