How does recruiting different muscle fibers relate to performance?
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Calling upon Type II fibers is sort of a win/lose situation for performance. It is a winner in that it will allow us to generate a lot more force to perform an exercise. However, it is a loser in that the exercise will become fatiguing as more lactic acid is generated in Type II fibers. This is why 5K runners cannot sprint the entire race. What they will do is run at the highest level they are able to, but that also keeps them from fatiguing before the end of the race. Their brain will call upon enough Type II muscle fibers to generate more force to allow them to run faster, however not enough Type II muscle fibers to generate critical levels of lactic acid and other factors that would result in fatigue before they cross the finish line. |
Do successful athletes have an imbalance of muscle fiber type?
Successful athletes seem to have an imbalance in muscle fiber types that favors excelling in a sport. For instance, successful sprinters often have a higher percentage of Type II fibers, allowing them to generate more force in a very brief period of time. This then allows them to be more powerful, generate more speed, and complete a sprint distance more quickly. Conversely, successful endurance athletes tend to have a greater percentage of Type I muscle fibers. This allows them to generate more force through aerobic energy systems in muscle cells. They can perform at a higher intensity before they generate critical amounts of lactic acid.
Are athletes born or developed?
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Often the question is asked whether top athletes are born or bred. The answer is both, but probably more of the former than the latter. Most very successful athletes are born (genetics) with the propensity to excel physically at a particular sport and training can then improve that potential. This is mostly true for sports that are endurance based or involve extreme power, as mentioned. An thletes genes direct the formation of more Type I or Type muscle cells and body design and potential for skill development to excel at one or more sports. Then to truly excel at a sport, the athlete must train and practice to optimize that performance. |
Can training allow muscle fibers to change type?
We do know that training results in changes in muscle metabolism which may make us think that it is possible for Type I fibers to change into Type II fibers and vice versa. However, this probably is not the case. For instance, endurance training can lead to changes associated with Type II muscle fibers that will make them more aerobic. The fibers will adapt to have an increased ability to generate ATP by using oxygen. However, they don’t adapt to the point where we would classify them as Type I. Oppositely, we all know that resistance training (e.g., weight lifting) improves the strength and power of a muscle group. Although it would be logical to think that half of this effect might be related to adaptations in Type I muscle fibers-as though they are being transformed into Type II muscle fibers-surprisingly this is not the case either. In fact, as the muscle group grows in size, most of the growth is related to enlargement (hypertrophy) of Type II fibers.
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