Which Muscle Fiber for Size

 There are two types of muscle fibers trainees are concerned with, Type I and Type II. Well, it breaks down a bit more than that. There are Type IIa and Type IIx. Let’s take a look at these muscle fibers and their importance for a healthier life.

Fiber Types

Type I fibers are aerobic and used in endurance training. You will see endurance athletes exemplify the use of this tissue type. Type II fibers are specialized for rapid, high intensity, explosive actions. The Type II group is what translates to size increases as the fiber bundles are thicker. 

If you were to physically remove the muscle fibers from each other you would see that the Type II is lighter in color than the deep red of the Type I. This is due to the absence of myoglobin and mitochondria. 

As you have noticed the Tupe II fibers are further divided into IIa and IIb/IIx fibers. Type IIa are a mix of Type I and Type II fibers. As such they do not fatigue as fast as the Type IIb/IIx. This gives a balance of endurance and power. Type IIb/x fibers are more inclined for powerful and explosive movements. To further illustrate the differences you have considered the endurance athlete. Now, consider a powerlifter versus an Olympic lifter. Both athletes rely on Type II muscle fibers for their sport; however, the Olympic lifter uses more Type IIb/x fibers for the explosive lifts. You see, a deadlift is simply powering the weight off the floor to the standing full extension. A power clean or snatch is moving the weight as fast as possible to the final overhead position. 

As Type II fibers are more anaerobic they are fueled more by glycogen than by oxygen. Glycogen is stored in the blood, to a small degree, and in the liver. These stores are depleted quickly in about 20 to 25 minutes.

Training

Type II are the fast twitch fibers. Training this type of fiber requires explosive movements. For instance on benchpress lower the weight with a slow controlled pace. When the bar touches your chest press as hard as you can. The idea is to pus the weight up quickly to activate the target fibers. 

Squatting looks similar. You maintain a slow, controlled decent then stand to full height quickly. There are some athletes who train with weighted jump squats. Adding unweighted jump squats after your sets are done is also an effective way to activate these fibers. 

The rest period between sets is recommended to be longer than normal. Three to five minutes is widely accepted as the rest period. 

Pause reps are also an effective means of targeting these fibers. For pause reps, if you have not done them yet, you pause at the muscle group’s full extension for two seconds or more. Then, contract. For example, you squat down to the deepest you can go and stay there for two to five seconds before standing upright. Bench is similar. You lower the weight until it’s just lightly touching your torso, hold it there for a few seconds, then press. 

Bent row and pulling exercises this looks a little different. In bent row you pause at the top of the rep, extend the period under contraction. 

Talk to your doctor before trying something new and stressful to your body. Make sure that you are healthy enough to do it. 

Train hard. Train safe.