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Old 02-25-2009, 10:52 PM   #3
Donald Lee
Senior Member
Join Date: Mar 2008
Posts: 620

Here are a couple easier to read articles:

Gram for gram, the two types are not different in the amount of force they produce, only their rate of force production. So, having a lot of fast twitch fibers only makes a positive difference when the time available for force production is very limited (milliseconds), like the 100ms or so the foot is in contact with the ground during a sprint or long jump. It makes no difference to the powerlifter who may use 3-4 seconds to execute a slow, smooth lift.. In cycling, the only event that they are decidedly advantageous for is the match sprint, analogous to the track 100 meter dash, but with more anticipatory tactics and theatrics.
Does Fiber Type Change with Training?
This has been one of the 10,000 dollar questions in exercise physiology. It has been documented that elite endurance athletes possess a higher percentage of slow twitch fibers in the muscles they use in their sport, compared to untrained individuals. Is this due to genetic endowment or years of rigorous training? The answer is difficult to get at directly because we don't have comparative muscle biopsies of great athletes before and after they started training and excelling in their sport. However, good basic investigation using experimental models has helped generate some answers. The critical knowledge to remember is that fiber type is controlled by the motor nerve that innervates a fiber. Unless you change the nerve, you won't change fiber types from fast to slow or vice versa. Just this type of experiment has been performed in animals (generally rats). So, remember, there is no compelling evidence to show that human skeletal muscle switches fiber types from "fast" to "slow" due to training..
The first article I posted seems to state that there is some evidence that fiber types do change. These articles were posted in 1996, while the first article was from 2000.
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