Your body has two major types of muscle tissues: fast twitch and slow twitch. The fast-twitch muscle fibers are known as the white muscle, while the slow-twitch muscles fibers are known as red muscle. These two types of muscle fibers are engaged differently depending on what type of activity you are doing. You can change the composition of your muscles to contain more red or white muscle fiber, depending on the goals of your training. Understanding the differences will allow you to create a fitness regimen designed to target the type of muscle fiber that most benefits your performance. It doesn't matter if you want to be thick, ripped, bulky, or just toned; exercise is how you get there.
Every bundle of muscle tissue is made up of slow-twitch red muscle fibers and fast-twitch white muscle fibers. How much of each you have is determined in part by genetics; however, the fiber types can change with regular exposure to different types of exercise. The American Council on Exercise suggests that the type and intensity of your training determines which muscles type dominates.
Red Muscle Fibers
Red muscle fibers are called slow-twitch muscle because they are built for endurance. These are the muscles you utilize for sustained movement. They are slower to contract but allow for a much longer workout. Long distance runners, cyclists and rowers rely heavily on red muscle fibers. The fibers are literally red in color due to the large number of blood vessels entwined with them. It's the blood that allows these fibers to produce energy for sustained periods of time. While most of the body is made up of a mixture of red and white fibers, the legs and back are made up of mostly red muscle.
White Muscle Fibers
White muscle fibers have earned the name вЂњfast twitchвЂќ because they contract in .01 seconds or less. Their contractions are fueled by oxygen, which contributes to the white color. Elite sprinters may have up to 80% more white muscle fibers than red since their performance relies on this type of tissue. White muscle fibers fatigue at a much faster rate than their red counterparts because of a buildup of lactic acid, so they are only good for short bursts of speed.
Training your muscle fibers means knowing what you want your end result to be; this goal determines what exercises you do and for how long you do them. To train for endurance sports, you want to engage your slow-twitch muscles. This means that you train at a lower intensity for longer periods of time with little rest between bouts. For example, if you are doing a weightlifting circuit, you would do several sets with several repetitions each of slow deliberate movements. To engage fast-twitch muscles used for explosive movements, like taking off on a sprint or swinging a golf club, do fewer sets of high-intensity moves with few repetitions each -- and do them fast.