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There are two types of skeletal muscle fibers in the human body – slow-twitch or Type 1 or Red muscles and fast-twitch or Type 2 or White muscle.
The fast-twitch contract with more force and many times faster than do slow-twitch ones. However, the fast-twitch ones fatigue more quickly.
Each of these muscle types can be further broken down into subcategories, depending on contractile speed, force and fatigue resistance. Type 2B fast-twitch fibers, for example, have a faster contraction time than type 2A.
Example 1 Pushing heavy weight for low repetitions is an activity that mostly involves fast-twitch fibers.
Example 2 Moderate intensity running on a tread mill is an activity that mostly involves slow-twitch muscle fibers.
Muscles cannot be converted from one type to another. Though to some degree, Type I fibers can be trained for enhance endurance and Type II can be trained to produce more force.
Endurance athletes have a greater proportion of slow-twitch fibers, whereas sprinters and jumpers have more of the fast-twitch variety.
How much of each muscle type a person has is determined by his or her genetics. Knowing the composition of our skeletal muscle type helps us choose a sport in which we can maximize our chances of winning. This knowledge also helps individuals and trainers with goals such as weight loss and be able to tailor their program according to their skeletal muscle composition.
Example 3 For a person seeking weight loss, having a higher composition of type I muscle fibers; his advantage is that he can sustain exercise for longer duration. He is fatigue resistant (do not easily get tired). The disadvantage is that he cannot perform power-intensive activities. Such a client can benefit from performing a mix of cardio and resistance training at medium intensity for a longer duration. This also allows him to engage in complex, whole body workouts resulting in good overall development and improvements in both cardio-respiratory and muscle health.