Isometric exercises refer to exercises where you contract your muscles without any movement. It involves holding a certain position or pushing against an immovable object to build strength and tone muscles. Full definition
10) Lift Weights — If this isn't possible, at the very least make sure you do a lot of isometric exercises such as pull - ups and pushups for resistance to be continually applied to your muscles. (leangainsguide.com)
Another great isometric exercise for the quadriceps can be done by standing directly in front of an immovable object such as a heavy table or bench. (unique-bodyweight-exercises.com)
The weakness of only performing isometric exercises is that you only get strong in one position. (ab-core-and-stomach-exercises.com)