This move stretches the quadriceps, the large muscles on the front of the thighs that we use for running. Stand facing the back of a chair (a wall or a tree also works; you just need a place to hold on to help you balance). Using the left arm on the chair for balance, bend the right leg and grab it with the right hand. Gently press the foot toward the buttocks until you feel the stretch in the front of the thigh. Hold for 10 to 30 seconds, and then switch legs.
You can also do this stretch with your opposite arm holding the foot. It is slightly more challenging to balance this way, but having the chair or other support helps.