Isometric exercises are contractions of a particular muscle or group of muscles. During isometric exercises, the muscle doesn't noticeably change length and the affected joint doesn't move. Isometric exercises help maintain strength. They can also build strength, but not effectively.
Because isometric exercises are done in one position without movement, they'll improve strength in only one particular position. You'd have to do various isometric exercises through your limb's whole range of motion to improve muscle strength across the range. In addition, since isometric exercises are done in a static position, they won't help improve speed or athletic performance. They can be useful, however, in enhancing stabilization — maintaining the position of the affected area — since muscles often contract isometrically to aid in stabilization.
Isometric exercises may be helpful to someone who has an injury, which could make movement painful. For instance, if you injure your rotator cuff, your doctor or physical therapist might initially recommend isometric exercises involving the group of muscles that helps stabilize the shoulder to maintain shoulder strength during recovery.
Isometric training may also be helpful to someone who has arthritis, which could be aggravated by using muscles to move a joint through the full range of motion. As people with arthritis perform isometric exercises and their strength improves, they may progress to other types of strength training. Strength training may help reduce pain and improve physical function.
Studies have shown that isometric exercises may also help lower your blood pressure. However, if you have high blood pressure, exercise at a lower level of intensity. Exercising at a higher level of intensity can cause a dramatic increase in your blood pressure during the activity.
Check with your doctor before beginning isometric exercises if you have high blood pressure or any heart problems. Avoid holding your breath and straining during any weight training exercise, as this may cause a dangerous rise in blood pressure.