An isometric exercise is an exercise involving the static contraction of a muscle without any visible movement in the angle of the joint. The term "isometric" combines the Greek words isos (equal) and -metria (measuring), 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.
The three main types of isometric exercise are isometric presses, pulls, and holds. They may be included in a strength training regime in order to improve the body's ability to apply power from a static position or, in the case of isometric holds, improve the body's ability to maintain a position for a period of time. Considered as an action, isometric presses are also of fundamental importance to the body's ability to prepare itself to perform immediately subsequent power movements. Such preparation is also known as isometric preload.