Isometric exercise or "isometrics" are a type of strength training in which the joint angle an muscle length do not change during contraction (compared to concentric or eccentric contractions, called isotonic movements). Isometrics are done in static positions, rather than being dynamic through a range of motion. The joint and muscle are either worked against an immovable force (overcoming isometric) or are held in a static position while opposed by resistance (yielding isometric).