More on Nike Free and Vitruvian philosophy -

The function of shoes, as I understand this philosophy, is to interfere with your stride the least amount possible - you wear them to protect your feet from broken glass, thorns, and porcupines. From Slowtwitch:
Modern shoes don't force runners to land on the heels, but with the heel slightly (and in some cases considerably) thicker than the forefoot area they certainly encourage it, particularly among slower runners. Landing on the heels isn't simply a question of asking the rocket science of today's shoe to absorb three to six times the body's weight - realistically, they can't. Landing on the heels requires the foot to remain in contact with the ground far longer. Apart from slowing the runner down, this form of footstrike makes little use of the important shock-absorbing arch muscles in the foot and in very many cases leads to problems of over-pronation. In the early years of a runner's life over-pronation is "corrected" (as the shoe giants would have it) by expensive stability shoes. In later years your podiatrist will be charging even more for custom orthotics.

More:
This is not new research. The information that harder midsoles attenuate shock better than soft soles has been public since 1987. "We've known about it for a long, long time," said Mr Bartold. The problem, he says, is that many sports shoe manufacturers have spent considerable amounts of money marketing certain products and are unwilling to change their marketing focus. "What you are dealing with is a very unusual crossover between hard-core science and a commercial product, and it's an unholy marriage."

And more:
Even with the best posture, running with a heel strike puts a greater loading on the quads and the iliotibial band, whereas forefoot running spreads the loading more evenly, encouraging muscle elasticity in the hamstrings, calves and foot flexors in absorbing shock and generating elastic rebound: calf and thigh muscles work together to absorb the body's weight. This relieves the knees, iliotibial band, hips and lower back and results in a far lower incidence of training injuries.

One more:
Gordon Pirie (former 5,000 WR holder) argued that 70% of running injuries today are directly attributable to the poor running shoes of today that force people to run incorrectly (and that correct running is injury free). The heel-strike character of most running shoes is troublesome. First, the heel is not a natural shock absorber. Your arch, and foot are the first areas of shock absorption while the achilles and calf muscles control pronation. Furthermore, landing flat footed allows for the knee to come over the foot and bend more quickly which allows the legs to take up more of the shock absorption. Some studies have actually shown that barefooted running is more shock absorbent than running in common running shoes.

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