Ever wonder why some people make better sprinters than marathoners? Or why chicken consists of white and dark meat? The simple answer: not all muscles are created equal.
Our muscles are made up of individual muscle fibers. These fibers fall into three different categories: slow twitch type 1, fast twitch type 2a, and fast twitch type 2b. As their names suggest, they also contract differently, serve different functions and impact the color of your chicken meat!
As the name suggests, contract slowly. They are associated with aerobic training – which means that they use oxygen to generate energy. Of all the muscle-fiber types, slow twitch fibers are the most resistant to fatigue and also the most efficient at burning triglycerides (the body’s fat stores).
Therefore, slow twitch muscle fibers help athletes run marathons or ride a bicycle for long periods of time. In humans, muscles that are predominantly made up of type 1 fibers include the postural muscles. Chicken legs also contain a large number of slow twitch fibers, which is why they can spend most of the day running around.
Also called “fast twitch glycolytic”, are the complete opposite of slow twitch fibers. The type 2b fibers contract very rapidly and generate a huge amount of power – but only for very short bursts. These fiber types are associated with anaerobic training – which means that they do not use oxygen to generate energy. Sports that are highly dependent on fast twitch type 2b muscles include the 100-meter sprint or the high jump. Chicken breasts consist mostly of this type of fast twitch muscle because chickens only fly to escape immediate danger.
Also called “fast twitch oxidative glycolytic”, are like the best of both worlds. They can generate energy either in the presence or absence of oxygen. With respect to fatigue and power, again, they’re in between both the type 1 and type 2b fibers. To continue with our running example, the distance most suited to type 2a muscle fibers would be the 1000 meters.
Generally speaking, humans have an even amount of slow twitch and fast twitch muscle fibers. However, certain factors may shift the balance in favour of one type over the other. Genetics is one major factor that scientists are trying to tease apart. And since we still haven’t developed an easy-to-use gene-testing kit, your best hint at your genetics is probably your body type:
Are typically very lean, with smaller shoulders and a very fast metabolism. These people are the lucky souls who can eat whatever they want and still somehow manage to stay thin. The muscles of an ectomorph are made up of a higher proportion of slow twitch (type 1) fibers. Not surprisingly, this body type is also the ideal for anelite marathon runner.
Have that stereotypical “athletic build”. They are strong and rectangular-shaped with defined muscles. When exercising, they find it very easy to build muscle mass. Mesomorphs have a higher proportion of fast twitch muscle fibers.
The good news is that even though our genes “think” they control everything, we can work around them. Each muscle contains a combination of all three fiber types. And, with the right kind of training, you can develop specific muscle fiber types. Scientists still aren’t sure if the muscle fibers actually convert from one type to another or if the fibers that are targeted simply get bigger. Regardless of the mechanism, it is nice to know that anyone can run a marathon with the proper training!
Also remember that our muscles are made up of a combination of muscle fibers for a reason. No sport is going to rely strictly on one type of muscle contraction. For example, marathoners need their slow twitch muscle fibers for most of their 26.2 mile run. However, the final sprint to the finish (especially if you’re trying to qualify for the Boston Marathon) will also require strong fast twitch fibers!