Isometric contractions generate force without changing the length of the muscle. Isometric exercise is also known as static strength training. Examples include the plank and side bridge as well as the wall sit and many yoga poses such as chair and tree poses. Notice that these are all exercises that involve holding a position rather than moving as is the case with isotonic exercise.
Because isometric exercises are done in one position without movement, they'll improve strength in only one particular position. Strength training may help reduce pain and improve physical function. Studies have shown that isometric exercises may also help lower your blood pressure.