Quadriceps, the muscle in the front of your thigh, is one of the most powerful muscles in the body. You use it for all the movements on the tennis court: running, jumping, lunging, and squatting. The more you use it, the shorter it gets, and the risk of injury increases. Often the risk is even higher if there are differences in the strength and flexibility between quadriceps and hamstrings. What makes it even worse is that after your hard practice where you used your quadriceps so intensely, you sit down and the legs stay in this shortened state for prolonged periods. Especially the upper part of the quadriceps and your hip-flexors get really shortened. That’s why it is extremely important to stretch it.