Gabe Mirkin, M.D.
Can you become very strong by doing isometric exercises in which you push against something that doesn't move, such as a wall?
The single stimulus to make a muscle stronger is to exercise a muscle against a resistance; therefore, you can become strong by doing isometric exercises. However, there are two drawbacks: isometrics can raise your blood pressure very high, and they make you stronger over a limited range of motion.
Everyone's blood pressure rises during exercise, but isometrics cause the highest rise of all. When you push against an object that doesn't move, your muscles contract and squeeze the blood vessels so hard that it raises blood pressure higher than with moving a weight continuously. Also, isometric contractions make you stronger only within 20 degrees of the angle you hold, but moving a weight make you stronger over a wider range of motion.