MORE INFO:

In an isometric muscle contraction, the muscle fires (or activates with a force and tension) but there is no movement at a joint.

In other words, the joint is static; there is no lengthening or shortening of the muscle fibers and the limbs don’t move.

In this type of muscle contraction, there is no change in the length of the muscle fibers themselves, and there is also no movement at the joints, but the muscle fibers still fire.

SOURCE:

https://www.verywellhealth.com/isometric-muscle-contraction-3120354