Justin has the right idea. Most people who work out regularly know that our muscles are made up of both fast-twitch and slow-twitch fibers, and that each of us has a different amount of each.
(Unfortunately, a lot of people don't even know this basic fact about exercise physiology...)
Even people who have a lot of fast-twitch fibers overall and are making good progress at bodybuilding will be frustrated by the fact that some muscle groups have a lot of slow-twitch fibers.
Like the calves... and the shoulders, too (shoulders)
Why? Think of a chicken, says my expert in exercise physiology.
Yes, it's a chicken. Most of the leg meat is dark... Full of blood vessels and slow-twitch muscle fiber, of course. Most of the time, the chicken walks around.
But the breasts, which are big wing muscles, are hardly ever used, EXCEPT when the bird needs to fly a short distance in an emergency. So the big muscles in the breast are "white meat," and most of them are made of fast-twitch muscle fiber, which grows quickly.
We're always on the move, so our calves are always working. These shoulder muscles are used every time we move our arms, even if the others are not.Muscle fibers are the parts that make up skeletal muscles. Not all muscle fibers are the same, just like not all muscles are the same. There are two types of skeletal muscle fibers: fast-twitch and slow-twitch. They each have different functions that are important to understand when it comes to movement and exercise programming.
Slow-twich Muscle Fibers
Slow-twitch muscle fibers don't get tired easily and are good at controlling posture and making small, steady movements. Compared to fast-twitch fibers, they have more mitochondria and myoglobin and work better with oxygen. Because they get blood, slow-twitch fibers are also sometimes called type I or red fibers.
Fast-twich Muscle Fibers
Fast-twitch muscle fibers can produce bigger and stronger forces, but only for a short time and until they get tired. They use less oxygen and get less blood. Because of this, they are sometimes called white fibers or type II. Skeletal muscles have both types of fibers, but the ratios can change depending on things like how the muscle works, how old it is, and how much it is trained.
Skeletal muscles have both types of fibers, but the ratios can be different depending on things like how the muscle works, how old it is, and how much it is trained. As a sports performance expert, it's important to remember how the two types of muscles are different.
Muscle Fiber Types: Slow Twitch Vs. Fast Twitch
Slow-twitch (type I) and fast-twitch (type II) muscle fibers are the two types (type II). Slow-twitch muscle fibers help you keep going for a long time, like when you run a marathon. Fast-twitch muscle fibers help you move quickly and powerfully, like when you sprint or lift weights.
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