Flexible calf muscles can improve your ability to increase the length of your stride, which results in increased speed. Loose calf muscles also take some of the burden away from your shins as you bring your trailing leg forward when running, helping prevent shin pain or shin splints. This basic calf stretch is an easy one to incorporate. Check out this video for more calf stretching demonstrations.
Stand facing a wall, about 12 inches away from it. Extend your arms in front of your shoulders to place your hands flat on the wall, keeping the elbows bent. Keeping both feet flat, step or slide your left foot (pictured) back, lengthening your left leg and straightening your arms. You should feel the stretch in the calf of the back (straight) leg. The more your lower your heel to the floor, and the farther you slide your straight leg behind you, the deeper you will feel this stretch. Breathe deeply and hold for 10-30 seconds. Switch sides.