Flexing muscles is a form of isometric exercise where the muscle is contracted, or squeezed, for five to 30 seconds, without any adjacent joint movement. A common example of an isometric exercise is flexing the arm by squeezing the biceps muscles. It is difficult to build muscles only through flexing as the there is not enough stress applied to the muscle fibers to elicit an adaptive response. Isometric exercises, however, can be part of a comprehensive body building program to enhance muscular endurance and definition.
Straighten both arms and cross the left arm over the right, at the elbow. Squeeze your chest as if trying to hold a pen between chest muscles. Hold for 10 seconds and repeat three more times, alternating which arm is on top.
Place both hands behind your back, just above the buttocks, grasping the left hand with the right. Keeping the legs straight, bend forward at the waist while lifting the arms as far overhead as possible to stretch the shoulders and upper back. Hold this position for 10 seconds and repeat three more times.
Place your hands on your hips and contract your abdominal muscles. Completely exhale and pull your abs in as far as possible toward your spine. Hold this position for five seconds and repeat three more times.
Position both arms so the upper arm is parallel to the floor, elbows extended to the sides. Flex each arm, squeezing the biceps and holding for 10 seconds. Repeat three more times.
Place both arms at your side. Activate the triceps by pretending to touch your wrist to the back of your elbow. Squeeze for 10 seconds and repeat three more times.
Extend one leg in front of you, from either a standing or seated position. Contract the thigh muscles on the front of your leg by straightening your leg as much as possible. Hold the contraction for 10 seconds and repeat three more times. Complete one cycle for each leg.
Lie on your stomach on the floor. Curl both legs backward attempting to touch your heel to your buttocks. This is similar to the biceps curl. Squeeze the hamstrings on the back of the thigh as hard as you can for 10 seconds. Repeat three more times.
Return to the standing position and place your feet together. Rise up on your toes, as high as you can, flexing your calves for 10 seconds. Rotate the heels outward for the second 10-second repetition, and the toes outward for the third 10-second repetition.
The key to making isometric exercises work is to squeeze the muscles to the point you are shaking. Watch a bodybuilder's posing routine and note how they quiver at the end of their routine. Done with enough intensity, isometric exercises can be quite taxing.
Avoid isometric exercises if you have high blood pressure. Prolonged static contractions increase blood pressure.