Isometric exercises involve the contraction of muscle tissue at a specific angle. These exercises are used to rehabilitate an injured joint rather than to improve overall strength, speed or endurance. If you have high blood pressure, isometric exercises are not recommended as the increased muscle tension tends to increase blood pressure.
Isometric means without movement. Another way of defining isometric is to break down the word -- iso means equal and metric is a measurement. In relation to strength training, equal measurement means your muscle remains at the same length. Your muscles will not contract and release or change length during isometric training, and your limbs and joints will remain in the same position.
One example of an isometric exercise is to grasp your hands together and press your palms toward each other. You can vary the angle by moving your hands closer to or father from your body. To use your body weight for an isometric exercise, hold a downward plank or the starting position of a push-up exercise for 10 to 20 seconds. Equipment can also be used to do isometric exercises. For example, hold a dumbbell in one hand, bend your arm to a 90 degree angle and hold the weight for 20 seconds.
Isometric exercises are easier on your joints if you have arthritis. Since isometrics do not involve moving a joint, those with arthritis can strengthen their muscles with limited painful side effects. You can also use isometric exercises to recover from an joint injury such as the knee. If you have torn a ligament in your knee and can't bend your knee, sit with your legs extended in front of you and lift and hold your leg off the floor.
You'll only improve your strength in the position in which you hold the isometric exercise -- you won't gain strength throughout the muscle's full range of motion. Isometric exercises do not build strength and these exercises are not used for building speed since movement is not involved in the training.