There are two main classifications of Muscle fibers. Type I (slow twitch) and Type II (fast twitch). 

 

Type II fibers are then divided into subclasses IIa, fast twitch oxidative-glycolytic) and IIx, fast-twitch non-oxidative.

 

Type I (Slow Twitch, Oxidative)

·         Slow contracting

·         Slow fatiguing

·         Small diameter

·         High number of mitochondria

·         High oxidative capacity (using fat stores as energy)

·         Good for low intensity prolonged activities such as maintaining posture and running long distance endurance sports

 

Type IIa (Fast Twitch, Oxidative-Glycolytic)

·         Good number of mitochondria

·         Can use both fat stores and glycogen stores for energy

·         Resistant to fatigue and recover quickly

·         Good for fast, repetitive, low-intensity activity. Bodybuilders posses high numbers of Type IIa muscle fibers, and research suggests they play a big role in muscle size.

Type IIx (Fast Twitch, Non-Oxidative)

 

·         Low number of mitochondria

·         Large in diameter

·         Fast fatiguing

·         Good for High-Intensity Interval Training, large-power output, such as sprinting and explosive power lifting.

 

 

How we train Fast-Twitch Muscle Fibers

There are several ways to increase your ratio of Type II fibers. Here at HIIT-Gravity Fitness, we focus on body weight strength training, speed training with resistance, as well as plyometric training.

Training in this fashion does several things:

 

1.   Hypertrophy of the Type II fibers, increasing their power output.

2.   Improve the recruitment of Type II fibers quicker.

3.   Convert Type I fibers to Type II fibers.

 

Strength training and speed training is very effective in developing maximum force. You can also achieve maximum force by lifting a lighter weight with fast acceleration.

HIIT-Gravity and Plyometric training are incredibly effective ways to develop fast-twitch fiber recruiters. We do it by using the stretch shortening cycle (SSC), which involves a pre-stretch of the muscle followed by a rapid contraction of the same muscle, resulting in the production of maximum force. We couple this approach with the Fitness Stride resistance system and other resistive forces such as body weight, dumbbells or kettle bells to help achieve the desired results.  

Long-distance endurance training (running and cycling) and lifting lighter weights for high reps focuses on the development of slow-twitch muscle fibers. Endurance training will reduce the amount of fast twitch muscle fibers. Limit the amount of endurance training to unless you want to decrease your fast-twitch muscle fibers.