Your muscles can generate force in several ways. As they lengthen, they create an eccentric contraction and as they shorten, they create a concentric contraction. Muscles can also remain fixed in position. This fixed or static form of contraction is called isometric contraction. Isometric exercises can be used to develop strength without the need for strength training equipment, which makes them ideal for workouts at home or while on the road. This type of exercise can cause a significant rise in blood pressure and thus is not suitable if you suffer from hypertension. Do not hold your breath when performing isometrics as this will also elevate your blood pressure.
Isometric Towel Curl
This exercise will strengthen your biceps brachii -- the two-headed muscle located on the front of your upper arm. Stand on the middle of a long towel and hold one end in each hand so that your arms are bent to 90 degrees and your thumbs are pointing up. Keep your knees slightly bent and your core muscles braced throughout. Contract your biceps as hard as you can and pull the ends of the towel upward. Hold this contracted position for 10 to 20 seconds and then relax. Rest a moment and repeat.
Self Resisted Triceps Push Down
This equipment-free exercise is an effective way to strengthen the muscles on the back of your upper arm -- your triceps brachii. With your hands clasped together, tuck your left elbow into your side with your palm facing downward. Using your opposite arm for resistance, push down as hard as you can. Hold this position for 10 to 20 seconds and then change sides. This exercise also benefits the biceps of your opposing arm.
The pullup is a powerful biceps and back exercise, but not everyone is strong enough to perform it. Isometric contractions are stronger than concentric and eccentric contractions and, subsequently, the isometric pullup is a more accessible exercise for many people. Using an underhand grip, stand on an exercise bench and grasp a sturdy overhead bar so that your chin is above the bar. Contact your biceps and remove your feet from the bench. Hold yourself in position for as long as you can and then put your feet back on the bench so you can rest. Focus on squeezing the bar and your biceps as hard as possible to get the most from this exercise.
Isometric Overhead Lockouts
Overhead lockouts are used by bodybuilders and powerlifters to develop strong triceps. Stand beneath a low door frame or roof beam. Reach up and place your hands against the overhead frame so that your elbows are approximately level with your head. Keep your knees slightly bent and your core muscles braced. Push your arms upward as hard as you can and hold this position for 10 to 20 seconds. Depending on your height and the height of your door frame, it may be necessary to stand on a sturdy exercise bench, step or stair to perform this exercise. As with all isometric exercises, avoid holding your breath.