From our friends from WebMD:
Shin splints, if that's what you have, can be caused by sudden increases in mileage, walking uphill, overtraining, walking faster than normal, jumping, running stairs, or just too much distance. They can occur on the medial, or inside of the shin, or on the lateral, or outside of your shin. Medial shin splints are usually caused by excessive pronation or flat feet, and often by pounding from running, or sports like tennis, volleyball, and other weight-bearing activities. If you have medial shin splints and flat feet or excessive pronation, an orthotic device or over-the-counter arch support like Powerfeet or Spenco can sometimes be helpful. Make sure it's a full-length insert.
Lateral shin splints (sometimes called anterior shin splints) are usually due to overuse and inflammation of the anterior tibialis muscle and the muscle compartment in the front of the leg, along the outside front of your shin. The anterior tibialis muscle flexes your foot upward. People frequently get anterior shin splints from the repetition of flexing the muscle. For instance, on the treadmill, if you walk fast enough, and for long enough, or if you've suddenly increased the speed, or you're walking on an elevation, the muscle gets overworked and starts to cramp. It would be like doing hundreds of biceps curls until your arm started to cramp. Plus, on the treadmill, there's no letup since the mill just keeps going. You could potentially have the same problem if you walked or ran briskly outdoors for a long period of time at a speed faster than you're used to.
Treatment for shin splints includes rest, massage, ice, stretching, and strengthening. Rest and ice is sometimes the best treatment. You should also be stretching your calves and Achilles tendon. If you have the problem during running or walking, try warming up more and don't increase the speed too quickly. You can also try varying the speed and elevation of the treadmill if you use one instead of keeping it the same.
To stretch your calves:
1. Lean against a wall with one leg forward and the knee bent
2. Keep the rear leg straight, heel on the floor
3. Keep your back straight and lean your hips forward until you feel stretch in your calf. If you don't feel it too much, put your toe of the rear leg up on a tree limb, or a dumbbell, or any other small object, so that you bend the ankle more. Your heel always remains on the floor. That will increase the stretch.
4. To stretch the soleus muscle and Achilles (very important for shin splints), do the same calf stretch but bend the back knee slightly and you will feel the pull on your Achilles tendon.
Also, make sure your shoes are sturdy and give you lots of support, particularly in the arch. If your shins hurt, you should gently massage them and then ice them after you work out.
Here are two web sites with pictures of exercises to stretch and strengthen your anterior tibialis: www.bodyresults.com and www.nismat.org. You can also go to www.nlm.nih.gov and enter "shin splints" in the search window.
Sometimes shin splints are confused with cramping of the anterior tibialis muscle and usually occurs from the constant repetition of flexing the foot. The anterior tibialis is the muscle on the outside of the shin bone that flexes your foot. Imagine sitting in a chair and constantly flexing your ankle up and down (i.e., tapping your toe) with your heel on the floor and in short time you will feel the same type of cramping. People report the cramping more often on the treadmill than outdoor walking, the reason being that on the treadmill the foot flexes repeatedly without any letup (unless you vary the speed). In addition, outdoors you self-select the speed and you probably vary it a bit which helps prevent the constant flexing problem at the same speed as on the treadmill. If you raise the elevation on the treadmill it can be even worse.
Some people report that running is not as bad as walking. This is most likely due to the fact that during walking you take more steps (and more flexes of the foot) than when you run. When you run your stride is longer and your feet are in the air for a longer period of time, which gives the foot a break from the constant contractions.
You can try a few things if this is the problem:
1. Vary the speed on the treadmill and try not to walk briskly for too long.
2. Warm up at slower speeds until you feel looser.
3. The web sites that I already posted above have some good exercises and pictures that should be helpful.
4. If the pain starts, either slow down the treadmill, get off and walk around for a few minutes, or as some people do successfully, start jogging to give the anterior tib a break.
Cramping usually gets better as your muscles get used to the treadmill, but every once in a while it will still cause a problem.