Competitive runners need at least two different types of shoes: one for training, one for racing. And, the proof is in the running.
When you run fast, you land on your heels with tremendous force -- equal to three times your body weight. This shock can break bones and tear muscles and tendons.
But, it's also the preliminary ingredient needed for speed and is actually helps save energy.
When your heel hits the ground, both the calf muscle and Achilles tendon in the back of your lower leg relax and stretch, storing much of the energy that is generated by your foot striking the ground. Then, as you move forward to shift your weight to the front of your foot -- just before stepping off -- the calf muscle contracts and the Achilles tendon springs back, driving you ahead. The energy released by this
spring-like motion is, in effect, a savings of two-thirds of the energy of the heel strike.
Obviously, padding the heel of a running shoe will help protect you from injury by absorbing much of the force of the heel hitting the ground. But, it will also dampen the spring-like action of the calf and Achilles tendon, slowing you down and wasting energy.
Therefore, training shoes -- worn when speed is not as important -- should have padded heels that will protect you from injury.
But, racing shoes should be made with heels constructed of a more resilient material that will not lessen the foot-strike force -- so the shoe can help to drive you forward with greater momentum. Racing shoes also weigh less, another factor that can help you run faster.Dr. Mirkin is a practicing physician in Silver Spring specializing in sports medicine and nutrition.
Competitive runners need more than one pair of shoes