A sufficient amount of muscular tension is necessary to elicit a physiological adaptation to weight training.
Weight training is essentially training the brain (nervous system) how to recruit motor units. Without losing too many people, a motor unit is a motor neuron and all the muscle fibers it innervates (5). There are 2 primary classes of muscle fibers: Type I, and type II. The type I fibers are referred to as slow-twitch. These fibers contract slowly and are harder to fatigue (6). These are the fibers primarily used when lifting light loads. The type II fibers are referred to as fast-twitch. They contract very rapidly and fatigue very quickly. Fast-twitch fibers can be broken down into types IIa and IIb. Type IIa fibers fatigue moderately and have properties of both type I and IIb fibers. Type IIb fibers fatigue easily and are used for short, high-force production tasks such as lifting heavy weights, sprinting, or jumping (6).
The fast-twitch fibers are primarily affected by lower rep sets. A decreased TUT will be used to stimulate these explosive muscle fibers, without causing too much fatigue to the nervous system. With this type of training, the brain is learning to synchronously recruit motor units in an attempt to perform the exercise.
This is why the speed of movement is very crucial. If you were to attempt to perform a set of 10 reps on the bench press, performing the concentric (positive) portion of the lift as fast as possible regardless of load, it would be impossible to replicate the same velocity on each rep. Consequently, fatigue results, and the quality of work is compromised. If the number of reps were limited to 2 or 3, the quality of work would be much higher.
Conversely, if you are training for hypertrophy (where an increase in muscle size is the main goal), then a greater time must be spent under tension to elicit a GH response, fatigue motor units, and produce contractile breakdown of muscle tissue. This will help to provide the body with a stimulus for muscle growth.
Another important issue to mention at this time is a concept referred to as Compensatory Acceleration Training (CAT). CAT assists in creating a greater amount of muscular tension by voluntarily attempting to recruit the fast-twitch motor units (10). When using this in your training, you must attempt to accelerate the weight as fast as you can during the concentric part of the lift. Don’t worry if the weight is heavy or moderate, if your intent is to move the implement as fast as you can, a greater proportion of fast-twitch motor units will be recruited. This is very important to athletes that perform in sports where speed is a determining factor. This can also benefit bodybuilders. The fast-twitch muscle fibers have a greater ability to hypertrophy. What better than a way to attempt to recruit them on every single rep