Isometric exercise means that you push against something that doesn't move, such as a wall. Thirty years ago, most weightlifters and athletes in sports requiring strength used isometric training, but you don't hear much about them anymore. The strength gained through performing isometric contractions is only within 20 degrees of the angle you hold. On the other hand, when you lift weights, you become strong through a wide range of motion. Isometrics cause your blood pressure to rise higher than the other methods of strength training. If you have weak blood vessels or heart trouble, you can rupture a blood vessel or develop an irregular heart beat.
According to Dr. John D. Fair, Chairman of the Department of History at Auburn University, the popularity of isometrics was the result of the success of some weightlifters who took synthetic male hormones called anabolic steroids and then claimed that their isometric exercises made them strong. They claimed that they were doing a revolutionary new training method of pushing against bars that didn't move. The steroids made them stronger by helping them to recover faster from tough workouts so they could do more work. The only stimulus to make a muscle stronger is to exercise that muscle against resistance. You can lift heavy weights, push against special strength machines and push against something that doesn't move, such as a wall or bar attached to the ground. Isometrics are not used much any more, but the steroids are still used, even though they are banned by most sport authorities.