Harvard evolutionary biologist Dan Lieberman believes that modern running shoes may explain why fifty percent of serious runners are injured at least once a year (Nature, January 2010). Modern running shoes have features that cause runners to land on their heels with forces of at least three times body weight at 6-minute mile pace. The faster a runner runs, the greater the force, which causes stress fractures of the feet and lower legs, shin splints, tears in the fascia on the bottom of the feet, knee and hip pain, tendon and joint damage and more.
Hitting the ground with the heel first generates tremendous force because it stops the foot suddenly. On the other hand, landing on the front of the foot allows the foot to keep on moving as the heel is lowered toward the ground to distribute the forces throughout the entire lower leg. If you drop a pen on its tip, it hits with tremendous force because it stops when it hits the ground and then falls forward. However, if the pen were dropped on the side of one end, it would hit the ground with much less force because after hitting on that side, the force would be distributed as the pen falls backward to the other end.
In the 1960s doctors thought that most running injuries were caused by excessive pronation, a rolling inward of the foot after the heal strikes the ground. They felt that the foot rolled inward toward the arch to dissipate the tremendous heel strike forces. This, in turn, caused the lower leg to twist inward and they blamed the frequent running injuries on the inward twisting motion of the leg after heel strike. So they invented running shoes with special arch supports to limit inward rolling, and with padded heels to cushion some of the shock of the heel hitting the ground. However, these features reinforce the runners’ habit of landing on their heels.
Dr. Lieberman has shown that barefoot runners are more likely to land on their forefoot or mid-foot. He has shown in elegant experiments that landing on the front part of the foot reduces the force of the foot strike very significantly. However, he has no data to show that running injuries can be prevented by running barefoot. Furthermore, stones and cut glass can cause injuries, and most runners have such thin skin on the bottom of their feet that they couldn’t possibly run barefoot.
New on the market are running shoes with very thin soles and minimal heels called Vibram FiveFingers shoe and the Dunlop Volley. Vibram is supporting Dr. Lieberman’s studies. Dr. Lieberman has shown only that
• modern running shoes tend to encourage a runner to land on his heels, and
• heel strike generates more force than front foot strike.
He has not yet shown that:
• modern running shoes cause injuries, or that
• injuries can be treated or prevented by running barefoot or in thin-soled shoes.
Dr. Lieberman’s website
Dr. Mirkin is a sports medicine doctor, fitness guru, and long-time radio host. Check out his website atwww.drmirkin.com.