The 3 Types of Muscle Contractions
There are 3 main types of muscle contractions: Isometric, Eccentric, and Concentric.
Isometric: An isometric contraction is a static action where the muscle generates force but there is no movement. When a barbell is held at the midpoint of the bicep curl, the biceps exert force but do not change in length. When the athlete places resistance against the curling movement, the biceps neither overcome the resistance, nor are they overcome by the resistance. The muscle length does not change even though it is contracting.
Generally, we are strongest in our isometric contractions [ie; standing still with a loaded barbell on our back.
Eccentric: An eccentric contraction occurs when the force generated by the muscle is less than the resistance, so the muscle actively lengthens. Eccentric actions are often used when muscles have to slow down body parts, control movements, or oppose external resistances. The downward phase of a biceps curl, for example, requires eccentric action of the biceps muscle. The muscle exerts force to control the speed of the downward movement, but its length increases.
Generally, we are 2nd strongest in eccentric phase [ie; lowering the bar to the bottom of the squat, but not being able to stand it up]
Concentric: A concentric contraction occurs when a muscle's force is greater than the resistance, so the muscle shortens such as in the upward phase of a bicep curl. Concentric muscle contractions are essential for overcoming the force of gravity and performing lifting movements.
Finally, we are generally weakest in the concentric phase of a lift.
Once these progressions are mastered for a specific movement, an individual may move on to dynamic contractions which combine the different kinds of contractions into one movement.
Here is an example of the pull up progression we use to build strength with the different types of contractions:
Chin over bar pull up hold [isometric]
Slow/weighted negative pull ups [eccentric]
Strict/weigthed pull-ups [concentric]
Kipping/Butterfly Pull Ups [dynamic]