How Does the Brain Know Which Type of Muscle Cells to Use for Different Sports

This is a no-brainer for the brain! This is because the brain will always call upon Type I muscle fibers first and then Type II. The major factor will be the required force to perform the exercise. For instance, when an exercise requires less force (for example, jogging, fast walking, casual cycling) the brain will for the most part call upon Type I muscle fibers (Figure 11.2). However, as the necessary force to perform an exercise increases (such as running, cycling fast, weightlifting), the brain will also

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Type I

Intensity

Figure 11.2 The order of recruitment of muscle fibers begins with our Type I fibers for lower intensity exercise (such as walking, casual cycling). As more force is needed, Type II fibers are also called upon (for example, in weight training, sprinting).

call upon Type II muscle fibers to generate force to support the force generated by Type I fibers.

How Does Recruiting Different Muscle Fibers Relate to Performance?

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 instead is run at the highest level they are able to, but that also keeps them from fatiguing before the end of the race. Their brains will call upon enough Type II muscle fibers to generate the force that allows them to run faster but not, however, 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. Con versely, 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.

People who excel at certain sports tend to have a genetic predisposition based on predominance of muscle fiber type.

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