All the muscles of the human body are made up of fibers. These fibers are split into three categories, namely: Fast Twitch Type 1, Fast Twitch Type 2 and Slow Twitch Fibers. Fast Twitch Fibers are both activated on the low rep ranges (6-12), and we consider them as one type of fiber. On the other hand, Slow Twitch Fibers are activated in the high rep range.
Each muscle group will contain all three of these fibers, but in different ratios. For example you may have 50:50 ratio in a muscle that consists of 50% Fast Twitch and 50% Slow Twitch. These ratio’s are arbitrary, and are unknown.
Most of the time, I see people training in 6-12 rep range, meaning they are only working Fast Twitch Fiber. This means they are not activating Slow Twitch, which results in a high amount of muscle fiber not being activated. This is a great loss of potential muscle growth.
This is why, I always encourage the us of all rep ranges into a training regime. The way I like to do this is to spend a week or two in the Fast Twitch region, and the week after that use high rep training to activate the Slow Twitch Fiber’s. Always remember, if you aren’t training the entire muscle, you will see limited growth.
Train across rep ranges, and you will see a difference.