Almost all modern running shoes are designed with massive amounts of cushioning and stabilization features in the heel in order to facilitate running with a heel strike. But if you look at the top finishers in a race of any distance from 100m to marathon the competitors are wearing what are called "racing flats," which have absolutely no heel cushioning, and no stabilization features. And the runners all run with a forefoot strike. What's up with this?
We have a lot of folks at CrossFit Atlanta who don't like to run because it hurts their knees, or their back, or causes some other injury process. In every case we find that they are running with a heel strike, and in every case the pain and discomfort goes away when we teach them to start running with a forefoot strike.
When running with a heel strike, a straight leg projects out in front of the runner at the moment of ground contact, and there is at that moment a ballistic load of several times body weight transmitted from the heel to the ankle, thence to the knee, the hip, and the back. There is also a jolting, braking action with each such step.
When running with a forefoot strike, the runner's foot makes ground contact directly under the body with bent ankle, bent knee, and a slightly open hip joint. There is no braking or jolting force. This is a natural shock absorption mechanism designed by 500,000 years of evolution.
An easy way to convince yourself that forefoot running is natural and heel strike running is unnatural is to go to a grass surface, take off your shoes and run barefoot. When barefoot it is painful and almost impossible to run with a heel strike.
There is a wealth of information on this subject on the internet. Google "Barefoot Running" and you'll come up with hundreds of websites dedicated to this most natural way of running. The Pose Method advocates a forefoot strike and sells instructional materials and seminars on how to develop a forefoot running style. Their discussion board is an excellent resource for finding racing flats and shoes that suit this style. The best free resource is the Gordon Pirie website. Pirie was an Olympic medalist in 5,000m at the 1956 Olympics in Melbourne, Aus. He later coached Olympic medalists at all distances up to marathon. He was the original consultant to Adi Dassler in the design of the early Addidas shoes. Pirie was a vigorous advocate of forefoot strike running, and presents a powerful argument that heel strike running is dangerous. His book, "Running Fast & Injury Free" is a free download at the website. Chapter 3 contains his analysis of running mechanics, and discussion of the history of how the faddish heel cushioning, heel strike shoes came to dominate the industry. Highly recommended.
If you are switching from heel to forefoot you will experience soreness in the calves until they get strong enough to go the distance. Jumping rope is excellent training to facilitate forefoot running.