Muscle fiber types explained simply

Skeletal muscles are fascinating structures that house three main types of muscle fibers, each with unique characteristics that define their function in the body. These fibers can be classified based on two criteria: their speed of contraction relative to other fibers and how they regenerate energy.

This is known as Henneman’s size principle it helps the body avoid fatigue by using no more Force than necessary. The fibers that create our muscles are like a rope woven together with fibers of different colors. Some colors run deep within the rope while others sit close to the surface.

Interestingly, the percentage of these colors can vary from one part of the rope to another. Our lower body or upper body may have greater concentration of one color than the other based on genetics and lifestyle choices. Just like a rope, our muscles also adapt to the specific type of training or injuries they undergo. Changes in the percentage of colors in the rope's fibers occur over an extended period of time.

Type 1 fibers, "slow twitch"

Endurance athletes may have more of the slow twitch muscle fibers in their bodies then power athletes, for example. Different types of exercises, such as a resistance routine or jogging, can either increase the size of one color or cause it to decrease.

Type 1 fibers, also known as "slow twitch" or "twitch" fibers, contract relatively slowly and consistently rely on oxygen to produce energy for the body. Imagine a marathon runner; just as they must have endurance and stamina to complete the long race, Slow twitch fibers are ideal for sustaining steady, low-intensity activities that require the body to hold a position or stabilize bones for extended periods.

Type 2A fibers, "fast oxidative"

On the other hand, Type 2A fibers, also called "fast oxidative" fibers, contract quickly and use a combination of oxygen and glucose as a source of speedy energy.

Think of them as runners or joggers, invoking the powerful movements needed for instant acceleration. Although not resistant to fatigue like Type 1 fibers, they still have enough endurance to be utilized in various aerobic exercises such as jogging, which require more energy than postural control but less than an explosive movement such as sprinting. 

Type 2B fibers

Type 2B fibers are the equivalent of speed demons in the world of muscles, as they have fast contractions and primarily use anaerobic glycolysis for energy. Picture them as sprinters, with a need for quick bursts of energy that allow them to produce high levels of tension. However, they come with a downside they tire out quite quickly, and fatigue much faster than other muscle fibers. This is because they have a large diameter and carry a high amount of glycogen that can be used to generate energy rapidly. They are best suited for activities like heavy weightlifting and sprinting, where short-term bursts of power are required.

In contrast, Type 1 fibers are like endurance athletes, capable of sustaining low-intensity activities for long periods without tiring out. Type 2A fibers are the middle ground, possessing qualities of both slow and fast-twitch fibers. In any activity, all three types of muscle fibers work together to meet the body's energy requirements. However, the type of activity being performed determines which fibers are recruited first. 

If you're doing a low intensity activity most of the fibers will be type 1 but if you're sprinting most will be type 2. To minimize the amount of fatigue the body first recruits the type 1 slow twitch fibers. After those fibers are maxed out the 2A fibers will be recruited and then type 2B. Henneman’s size principle explains that smaller motor units are recruited first during low-intensity activities, and larger ones are brought in as the level of activity increases to complete a movement this table summarizes the different characteristics of the three types of muscle fibers.

By understanding the unique characteristics of each muscle fiber type, we can tailor our workouts to optimize our performance and achieve our fitness goals.