When scientists began exploring different muscle types, muscle fibers were categorized based on their color: red and white muscle fibers. Red muscle fibers have more blood vessels and mitochondria, which gives them their red appearance, hence the name "red muscle fibers." The other type, with fewer blood vessels and mitochondria, appears white and is called "white muscle fibers." White muscle fibers can grow up to four times larger and contract 2 to 3 times faster than red muscle fibers. That’s why white muscle fibers are also called fast-twitch fibers, while red fibers are known as slow-twitch fibers. Bodybuilders and short-distance sprinters aim to develop white (fast-twitch) fibers, whereas marathon runners and cyclists prefer red (slow-twitch) fibers because they are more energy efficient.
Type 1 (Red) — Slow Oxidative
This is the slowest muscle fiber type but highly resistant to fatigue. It contains a lot of myoglobin, mitochondria, and blood vessels. ATP is generated aerobically (oxidative fibers), and ATP is split slowly. These fibers contract slowly and resist fatigue well, making them ideal for endurance sports like marathons and triathlons. They are also important postural muscles and high-endurance muscles such as abdominals and forearm muscles.
Type 2a (Red) — Fast Oxidative
This fiber is similar to Type 1 but contracts faster and is still fairly resistant to fatigue. It contains a lot of myoglobin, mitochondria, and blood vessels. ATP is generated aerobically but split faster than Type 1 fibers. This muscle type is suited for activities like middle-distance running and ice skating.
Type 2b (White) — Glycolytic Fiber / Fast Twitch B
This is the fastest muscle fiber type with less myoglobin, mitochondria, and blood vessels. It contains a large amount of glycogen, meaning energy (sugar) is stored very close to where it is needed because it is used up quickly. ATP is split extremely fast, but these fibers fatigue rapidly. This fiber type is ideal for sprinting, bodybuilding, and sports involving explosive movements.
The more a muscle is used in daily life, the higher its percentage of red muscle fibers.
To train fast-twitch muscle fibers, you don’t need to move weights fast. Fast-twitch fiber training results from sets of 8 to 12 concentrated repetitions.
If you want to improve speed, check my section on plyometric exercises.
Top bodybuilders like Ronnie Coleman, Kevin Levrone, and Markus Rühl have a high amount of white muscle fibers. After all, only white muscle fibers can grow that large. Many people mistakenly believe bodybuilding makes you slow—this is nonsense! Technically, bodybuilding trains you to be fast. The reason many bodybuilders seem slow is:
If you still doubt this, visit YouTube and search for “Kevin Levrone Sprint” to see proof.
