Stretching your Plantar Fascia is as important as stretching your calf muscles, because if you don't it can nullify any stretch done to the calf muscles ... follow me? The pure and simple anatomy of the region is such that the Achilles Tendon and calf muscles pull on 1 side of your heel bone (the Calcaneus), and the Plantar Fascia pulls on the other side. If you stretch 1 side and not the other, the unstretched side can pull the bone more aggresively than the stretched side and this can play around with your biomechanics and eventually cause you serious pain and/or dysfunction. Regular thorough stretching can be your key to healthy well-being and body balance, enabling you to live without niggly aches and pains. Go the Stretch!
This stretch focusses on the back of your lower leg (or your calf region), and primarily the Gastrocnemius and Soleus muscles. It also stretches the sole of your foot, or the Plantar Fascia. Again, i'm sure everyone has heard of these muscles and knows exactly where to find them. You can stretch your legs singularly or both together, but I recommend stretching 1 leg at a time because it will increase the extent of the stretch and therefore give you a better result for your effort. Also, it is worthy of note to identify that if you place the ball of your foot on the edge of the step you can increase the stretch to the upper muscle fibres (closer to your knee), and if you place the mid section of your foot on the edge of the step you can increase the stretch to the lower muscle fibres (closer to where the muscle meets the tendon).
Stand tall on the edge of a step ... by this I mean elongate your spine - don't bend over, and be positioned so that the ball of 1 foot is on the edge of a step with the other safely in full contact with that same step. If you are not near steps, then a ledge of any kind will do (like a brick, or a box - anything that will safely hold your weight). Stabilise yourself by holding onto a rail or post so that you do not 'wobble' while you are stretching ... NOTE: wobbling could do more harm than good when it comes to stretching!
When you are stable and not wobbling you can begin to stretch. Take a deep beath in, then as you exhale lightly drop the heel of the foot on the edge of the step as far as possible. It should not be uncomfortable, and you should feel the stretch both through calf and under your foot.
Hold this position for 15-20 seconds (don't hold your breath), then gently release the tension and repeat on the other leg.
Try to keep your body long - that is don't slouch or hunch over. Also be very aware of not wobbling. Wobbling will make other mucsles fire to stabilise the body and that will detract from your stretch. It may also lead to ankle injury in a worst-case-scenario.
Don't 'bounce' when you stretch. You can safely take your whole body weight through this stretch, and you can even hold this stretch for a few minutes if you feel you want to, but do it gently and securely. Bouncing in a stretch (or Ballistic Stretching) can put unnecessary stress on the musculotendinous junctions, and even cause micro tearing of muscle fibres which can lead to pain and injury.
Variation to focus on the Soleus Muscle:
When your leg is straight the stretch will have effect on all muscles that cross the knee and ankle joints. The Soleus does not cross the knee joint, so to thoroughly stretch your calf you will need to do some reps with a straight leg, and then some reps with a slightly bent knee. The bent knee takes your Gastrocnemius out of the stretch and places a greater focus on the Soleus.
Always remember to relax into your stretches - don't fight against the stretch (it may cause more harm than good), and always do each stretch 3 times, at least twice each day.
Taken from "Stetching Anatomy" by A.G.Nelson and J.Kokkonen - pp 132-133