Isometric exercise is a form of exercise involving the static contraction of a muscle without any visible movement in the angle of the joint. This is reflected in the name; the term "isometric" combines Greek the prefixes "iso" (same) with "metric" (distance), meaning that in these exercises the length of the muscle and the angle of the joint do not change, though contraction strength may be varied. This is in contrast to isotonic contractions, in which the contraction strength does not change, though the muscle length and joint angle do.
Resistance in isometric exercises typically involve contractions of the muscle using:
The body's own structure and ground
Structural items (e.g., pushing against a fence)
Free weights, weights machines or elastic equipment (e.g. holding a weight in a fixed position)
Pressure plate type equipment that has a digital display of maximal force.
Depending on the goal of the exercise, the exertion can be maximal, or sub-maximal.