Muscle Fiber Type

Type I: Slow Twitch Fibers.

Type IIa: Fast Twitch Fibers.

Type IIb: Fast Twitch Fibers


Type 1 fibers are slow to contract (hence, slow twitch), and can sustain muscular contractions for an extended period of time. This factor makes them ideal for endurance type of events where one is exercising for long durations. They also contain large and numerous mitochondria which aid in their oxidative metabolism (the use of oxygen). These types of fibers are fatigue resistant but are only able produce a relatively low level of force output.

Type IIa muscle fibers are, as the name would suggest, fast twitch fibers (FTF's). However they are in the middle of the muscle fiber spectrum, as they are less fatigue resistance, produce more muscular force, and contract at a faster speed than slow twitch fibers, but not quite as much as type IIb fibers.

The type IIb fibers are the most easily fatigued out of all the fibers but also generate the most power. These are most heavily recruited for activities that require an all out burst of power over a very short period of time.

It is the type IIb fibers that are primarily responsible for your vertical jump performance, although your type IIa’s also have a small role. As such it is the type II's that you should be targeting with your training.

Table 1: Fast-twitch muscle percentages compared
Subject	Fast-twitch muscle fibre (%)
Sedentary	45-55
Distance runner	25
Middle distance runner	35
Sprinter	84

How To Train Your Muscle Fiber Type

When you're training with weights, your goal is to work as many muscle fibers as possible. Affecting more muscle fibers means greater gains in strength and muscle mass.

If your fibers in a particular muscle consist primarily of slow twitch fibers, in order to affect the greatest number of those muscle fibers, you'll need to train that muscle with higher reps, shorter rest periods and higher volume. This is because they take longer to fatigue, they recover quickly and they require more work to maximize growth.Higher reps (e.g. 12 to 15 reps), higher volume (more sets) and shorter rest periods (30 seconds to a minute between sets) can help you to maximize those muscles.

This doesn't mean you should use light weight, though. You should still strive to use weights that are as heavy as possible that will cause you to reach failure in those higher rep ranges. If you don't use heavy weights, you won't give your muscles a reason to grow.

If your fibers in a particular muscle group consist primarily of fast twitch muscle fibers, you're one of the lucky ones. You'll have a much easier time building mass in that muscle - fast twitch muscle fibers have greater potential for size than slow twitch. The more fast twitch fibers you've got, the greater your ultimate muscle size can be. These muscles are most likely your strongest and quickest to develop.

To maximize your muscles with fast twitch fibers, you'll need to train with low to moderate reps (e.g. 4 to 8 reps), rest periods of around 1 to 2 minutes and a moderate training volume (too much volume will compromise recovery).

If your muscles have a fairly even mix of fibers, you can evenly divide your training between focusing on the lower-rep, fast twitch fiber training and the higher-rep, slow twitch fiber training. This will help you to develop all the fibers in your muscles, maximizing your ultimate development.

Conclusion
In order to get the most out of your vertical jump training, you should try to follow those principles. A vertical jump is a powerful, type II muscle fiber based contraction that takes place in a split second. The most effective and efficient way to train therefore is to ensure you fully develop those fiber types. Anything else is just wasted time and energy.