Test: Lie on your stomach with both legs straight. Now raise the foot of one leg towards your butt. Grasp the ankle with your hand and, without lifting your thigh off the floor, hyperextending your lower back or pulling your knee from the body, bring your heel to your butt. Can you reach your hip with your heel?
Movement: Lie prone on your stomach with both legs extended straight. Gently flex one knee and raise the heel towards your butt. With the hand on the same side of the body reach back and grasp your ankle. Now pull the ankle towards your butt, not allowing the thigh of that leg to leave the ground or your lower back to hyper-extend. If you cannot touch your heel to your butt, your quadriceps are very likely tight.
Repetitions: Hold for the full prescribed time on one side, then switch sides and repeat. This counts as one set.