DEFINITELY FORCE IT!
Simplified, skeletal muscles develop force, that is used to pull on a tendon, that in turn, pulls on a bone, resulting in skeletal movement. Yet, how is that muscle force developed, and how is it applied to the joint, can create diverse muscle work dynamics. We commonly address five (5) different muscle work dynamics:
Concentric muscle work
Eccentric muscle work
Isometric muscle work
Isotonic muscle work
Isokinetic muscle work
When a muscle develops force/strength via concentric muscle contraction (contraction meaning force production), the sarcomere which is the smallest force producing component within a skeletal muscle, does so by shortening towards the middle. "Con" means towards, and "Centric" means the center or the middle. We often use concentric skeletal muscle work when the skeletal muscle pulls in the opposite direction to the application of gravity onto our body (overcoming gravity), in order to bring something closer to us ("hug movements") or while transitioning into the fetus position.
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When a muscle develops force/strength via eccentric muscle contraction, the sarcomere does so by elongating outwards toward the outer ends of the muscle. "Ec" means outwards from, and "Centric" means the center or the middle. We often use eccentric skeletal muscle work when the skeletal muscle pulls in the same direction to the application of gravity onto our body (submitting to gravity, or working with it), in order to move something away from us ("hug movements") or while transitioning into the anatomical position.
When a muscle develops force/strength via isometric muscle contraction, the sarcomere does not change its length (it does not elongate nor shorten). "Iso" means the same or no change, and "metric" means length. We often use isometric skeletal muscle work when the skeletal muscle pulls at the same extent that gravity is resisting at (balancing out gravity, or canceling out its effect).
When a muscle develops force/strength via isotonic muscle contraction, the sarcomere develops the same amount of force/strength throughout the entire range of motion of the joint. "Tonic" means force production extent (based on the muscle tone extent created in the skeletal muscle). We often use isotonic skeletal muscle work in order to fixate muscle force production, independent of the speed/pace of movement throughout the range of motion that the joint allows.
When a muscle develops force/strength via isokinetic muscle contraction, the sarcomere develops force/strength in a way the results in the same speed/pace of movement throughout the range of motion of the joint. "Kinetic" movement, and in this case specifically, movement speed. We often use isokinetic skeletal muscle work in order to fixate the ratio of degrees of movement per second, independent of the extent of muscle force/strength production required to sustain the same movement speed.
While isometric skeletal muscle work is a static (non-dynamic) form of skeletal muscle work, the other four (concentric, eccentric, isometric, and isokinetic) are dynamic forms of skeletal muscle work. Static means there is no change to the angle of the joint, while dynamic means the angle of the joint does change.
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