The gastrocnemius (calf) muscle crosses both the ankle joint and the knee joint.  So it is imperative that the knee joint not flex at all during this stretch.  This stretch is great for people suffering from shin splints and Achilles tendon problems.

To perform the gastrocnemius stretch:

1. Sit with your right leg straightened out in front of your with your right knee locked.
2. Contract the muscles on the front of your right lower leg (tibialis anterior) to pull the foot back.
3. Using your hands, or a rope/towel wrapped around your foot, gently apply 1 lb. of force in the direction of the stretch.
4. Hold this position for 1.5 - 2 seconds and then return to the neutral position.

Repeat the above steps for a total of 2 - 3 sets of 10 repetitions on the right and 10 repetitions on the left.  Alternate legs after each set.  If you are using this stretch as a general warm-up, only perform 1 set of 10 repetitions per leg.

Keep your low back flat while performing this exercise.  Gradually lean your upper body forward by bending at the waist for a greater stretch.