There are three different types of muscle in the body.
Regulates all the autonomic functions you perform without thinking, like regulating light with the pupils, moving food through the GI tract, and these play a large part in the ‘fight of flight’ response.
This muscle deals with your heart. It is strengthened through endurance training, such as long runs, yoga, and other type of aerobic exercises.
Skeletal muscle is the kind we like, it is the kind we can see when flexing in the mirror, and is the kind that allows us to move our legs or lift dumbbells. When exercising to build muscle or increase performance you are strengthening the skeletal muscle.
Skeletal muscle isn’t as simple as it seems though. You may be familiar with the term “dense muscles”. Truth is “dense muscle” doesn’t exist. All muscle tissue is close to the same density. However, some muscle is going to be more capable of burning large amounts of energy in shorts bursts, this could perhaps give the illusion of density.
There are two types of skeletal muscle, slow-twitch and fast-twitch. The only difference between the two types of muscle is the metabolic pathways that run through the muscle tissue. Muscle is muscle whether it is slow-twitch or fast-twitch, it is still good to have. What I am trying to say is that one isn’t better than the other, but they are different.
-Slow-twitch muscle is wired with metabolic pathways that burn energy slowly. This is good for aerobic exercises.
-Fast-twitch muscle is wired with metabolic pathways that burn energy very quickly. This is good for weight lifting and sprinting.
For the most part people have an even split 50 percent fast-twitch muscle and 50 percent slow-twitch muscle. However it is not uncommon to see Olympic sprinters with 80 percent fast-twitch muscle, and marathon runners with 80 percent slow-twitch.
You shouldn’t be concerned with what type of muscle you are developing. Just do what you do and let your body develop normally. You will naturally develop the most functional muscles for whatever activities you are performing. However, know that if you are going to run a marathon, then you have to start training to build some slow-twitch muscle.