There are two different types of muscles in the human body - they go by the snappy names Type I and Type II, though most people know them better by their non-scientific names, slow-twitch (Type I) and fast-twitch (Type II).
Knowing the types of muscles and how you want to use fitness training to get healthy means that you can train smarter. These names started to enter into the common vocabulary in the 1970s, as scientists started to realize that there were clear scientific reasons why some of us are better at endurance sports, while others excel at events requiring power and speed.
Most muscles are made up of a combination of Type I and Type II fibres. The characteristics of the two are as follows:
- Type I muscles have a slow contraction or "twitch" time, have increased resistance to fatigue, and are well suited for activities requiring strength and endurance that depend on oxygen - aerobic or cardiovascular work.
- Type II muscles are less suited to continuous types of activity, more suited to fast work. They can work in an oxygen-free environment (anaerobic work - sprints, heavy lifting).
Although most muscles of the body are a mixture of muscle fibres, their proportion varies depending on the normal action of the muscle. For example, muscles of the neck, back, and leg have a higher proportion of Type I fibers, while the muscles of the shoulders and arms, which are used more intermittently, have a higher proportion of Type II fibres.
What is interesting is that various types of exercises can bring about changes in the fibres in a skeletal muscle. Endurance exercises, such as running or swimming, cause a gradual transformation of type II fibres into Type I, while workouts that require bursts of strength for short periods of time, such as weight lifting, produce an increase in the size and strength of type II fibres. The result? You develop larger muscles.
It therefore makes sense to think about what your goals are for your exercise programme - understanding the different muscle types will help you to focus on the types of exercise that are right for you.