Your muscles are made up with fibers, slow twitch and fast twitch. Slow Twitch (Type I) are more efficient at using oxygen to generate more fuel (known as ATP) for continuous, extended muscle contractions over a long time. They fire more slowly than fast twitch fibers and can go for a long time before they fatigue. Therefore, slow twitch fibers are great at helping athletes run marathons and bicycle for hours. Fast Twitch (Type II) use anaerobic metabolism to create fuel, they are much better at generating short bursts of strength or speed than slow muscles. However, they fatigue more quickly. Fast twitch fibers generally produce the same amount of force per contraction as slow muscles, but they get their name because they are able to fire more rapidly. Having more fast twitch fibers can be an asset to a sprinter since she needs to quickly generate a lot of force.
You may notice that some people are better at long slow distance training and others are better at sprinting or heavy lifting. It is not always because they train specifically for those events, it is has a lot to do with their distribution of slow twitch and fast twitch fibers in their muscles. Every person is a unique flower and has a different combination of fibers and you cannot change that. You can work on specific training to target each type of fibers to improve them. In CrossFit we do train all of these fibers by the variation in reps, load and intensity.
There are two classifications of Type II fast twitch fibers, they are:
Fast Twitch Muscle Fibers: Type IIx: This subtype of fast twitch muscle fibers contains small amounts of mitochondria, which means these muscles do not do as well during long duration workouts. These muscles have a small capacity for aerobic metabolism, and fatigue more easily than their slow twitch counterparts. These fibers can’t sustain their effort for more than a few seconds. Think of sprints and low rep heavy lifts.
Fast Twitch Muscle Fibers: Type IIa or Fast-Oxidative Glycolytic Fibers: This subtype has the same characteristics as mentioned above with a few differences. These muscles possess properties of speed, fatigue, and force production somewhere between type I and IIx fibers, therefore they can work up to three minutes in elite athletes. People in this category are highly adaptable. They are able to increase their oxidative capacity to levels similar to that of the slow twitch group, but at a cost. When people in this subtype go into the oxidative capacity, they tend tolose more muscle mass, therefore, losing some of the strength portion of their overall fitness.
It may sound like these type of muscles are just awful, but here are the benefits of this type of muscle tissue. These muscles posses a higher number of glycolytic enzymes. What does this mean? It means these muscles perform anaerobically; so they do not need oxygen to produce ATP. With these characteristics, these muscles have the ability to produce a lot of force (lifting), but in short durations. Ultimately, these muscles are tailor-made for lifting in that they do well with short, explosive movements. But when it comes to metabolic conditioning or a long duration CrossFit WOD like “Eva,” people in this category work much harder to sustain and keep their muscles from fatigue. Endurance is something people in this category need to work on.
For more info about these fibers, check out this post: http://breakingmuscle.com/crossfit/the-crossfit-dilemma-why-can-t-i-lift-more-than-that-person
Today’s workout is a 2o minute AMRAP with gymnastics/body weight movements. In a workout like this, it is not a sprint, we are working on building up muscular endurance. Find a pace and stick with it through the whole workout. In this workout we are working on training the fast twitch Type IIa muscle fibers.
