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Are you a better sprinter or distance runner? Many people believe thathaving more fast and slow twitch muscle fibers may determine whatsports athletes excel at and how they respond to training. Skeletal muscle is made up of bundles of individual muscle fiberscalled myocytes. Each myocyte contains many myofibrils, which arestrands of proteins (actin and myosin) that can grab on to each otherand pull. This shortens the muscle and causes muscle contraction.
It is generally accepted that muscle fiber types can be broken down into two main types: slow twitch (Type I) muscle fibers and fast twitch (Type II) muscle fibers. Fast twitch fibers can be further categorized into Type IIa and Type IIb fibers.
These distinctions seem to influence how muscles respond totraining and physical activity, and each fiber type is unique in itsability to contract in a certain way. Human muscles contain agenetically determined mixture of both slow and fast fiber types. Onaverage, we have about 50 percent slow twitch and 50 percent fasttwitch fibers in most of the muscles used for movement.
Slow Twitch (Type I)
The slow muscles are more efficient at using oxygen to generate morefuel (known as ATP) for continuous, extended muscle contractions over along time. They fire more slowly than fast twitch fibers and can go fora long time before they fatigue. Therefore, slow twitch fibers aregreat at helping athletes run marathons and bicycle for hours. What Causes Muscle Fatigue? Fast Twitch (Type II)
Because fast twitch fibers use anaerobicmetabolism to create fuel, they are much better at generating shortbursts of strength or speed than slow muscles. However, they fatiguemore quickly. Fast twitch fibers generally produce the same amount offorce per contraction as slow muscles, but they get their name becausethey are able to fire more rapidly. Having more fast twitch fibers canbe an asset to a sprinter since she needs to quickly generate a lot offorce. Type IIa Fibers
These fast twitch muscle fibers are also known as intermediate fast-twitch fibers. They can use both aerobicandanaerobic metabolism almost equally to create energy. In this way, theyare a combination of Type I and Type II muscle fibers. Type IIb Fibers
These fast twitch fibers useanaerobic metabolism to create energy and are the "classic" fast twitchmuscle fibers that excel at producing quick, powerful bursts of speed.This muscle fiber has the highest rate of contraction (rapid firing) ofall the muscle fiber types, but it also has a much faster rate offatigue and can't last as long before it needs rest. Fiber Type and Performance
Our muscle fiber type may influence what sports we are naturally goodat or whether we are fast or strong. Olympic athletes tend to fall intosports that match their genetic makeup. Olympic sprinters have beenshown to possess about 80 percent fast twitch fibers, while those whoexcel in marathons tend to have 80 percent slow twitch fibers. Are Athletes Born or Built? Can Training Change Fiber Type?
This is not entirely understood, and research is still looking at thatquestion. There is some evidence showing that human skeletal muscle mayswitch fiber types from "fast" to "slow" due to training.
These studies and journal articles offer more insight on muscle fiber research: High-Intensity Training and Changes in Muscle Fiber Nature vs. Nurture: Can Exercise Really Alter Fiber Type Composition? Effects of Endurance Training on Muscle Fiber What can I do to improve my performance?
Keep in mind that genetic differences may be dramatic at the elite levels of athletic competition. But following the principles of conditioning can dramatically improve personal performance of a typical athlete.
With consistent endurance training, muscle fibers can developmore and improve their ability to cope with and adapt to the stress ofexercise.
Is fiber type the number one factor that makes an elite athlete elite?Fiber type is part of a great athlete's success, but it alone is a poorpredictor of performance. There are many other factors that go intodetermining athleticism, including mental preparedness, proper nutrition and hydration, getting enough rest, and having appropriate equipment and conditioning.
Sources:
Andersen, JL; Schjerling, P; Saltin, B. Scientific American. "Muscle, Genes and Athletic Performance" 9/2000. Page 49
McArdle, W.D., Katch, F.I. & Katch,V.L. (1996). Exercise physiology : Energy, nutrition and human performance
Lieber, R.L. (1992). Skeletal muscle structure and function :Implications for rehabilitation and sports medicine. Baltimore :Williams & Wilkins.
Andersen, JL; Schjerling, P; Saltin, B. Muscle, Genes and Athletic Performance. Scientific American. 9/2000
Thayer R, Collins J, Noble EG, Taylor AW. A decade of aerobic endurancetraining: histological evidence for fibre type transformation. Journalof Sports Medicine & Phys Fitness. 2000 Dec;40(4).作者: 雪狼Wang.Z.G 时间: 2009-1-30 21:13
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