Muscle Fibers- Fast v. Slow Twitch
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Now taking a look into Fast-twitch Type II muscle fibers one will see that Fast-twitch muscle fibers are able to manufacture ATP quickly by the rapid splitting of glucose. This will help to sustain strong muscle contractions.
Fast-twitch muscle fibers also contain high amounts of creatine and phosphocreatine, which as we now know (from my previous article), coincides with ATP production. The Type II fast-twitch muscle fibers can be broken down into two categories. The two kinds of Type II muscle fibers are Type IIa and Type IIb. Type IIa muscle fibers are also known as fast-twitch oxidative glycolytic. Their glycolytic and oxidative aptitudes give them the ability to produce muscle contractions for a sustained period of time. Type IIb muscle fibers are also known as fast-twitch glycolytic. These fibers are very large and can produce great muscle contractions as they store plenty of ATP and PCr. Type IIb muscle fiber benefit greatly with the supplementation of creatine due to their abundance of PCr. Type IIb fibers will fatigue quickly once the ATP and PCr levels become depleted. So when comparing the two fibers, Type IIa will sustain longer, strong contractions due to its oxidative functioning, where as type IIb can only last as long as the ATP and PCr reservoirs last (hence why creatine is so important).
Vincent Russo, 25 years old from Kenilworth NJ. Has a BA in Biology from Fairleigh Dickinson University in Madison NJ. A Bodybuilding.com Team Athlete, Silver Model, High School Football Coach, Substitute Teacher, Waiter/bartender. Was a top 5 finalist out of 500 guys for bodybuilding.com‘s 2012 BodySpace Spokes Model. Compete in the Men’s Physique category where in recent competitions placed 2nd in NPC East Coasts (Nov. 2011), and 3rd in Bodybuilding.com‘s BodySpace Spokes model competition (LA Fit Expo 2012).