Since the summer of 2014, so almost two years now, I have been experimenting with minimalist shoes for running. These are shoes with little or no shock absorption, and little or no difference in height between the heel and forefoot ("zero drop"). In practice, the shoes sold as minimalist have varying degrees of shock absorption, and varying degrees of heel-to-toe "drop". The idea is that with shoes like this, one can run in way that approaches true barefoot running. The main characteristic of this natural running style is that the forefoot strikes the ground first when landing, which is something one does instinctively when running barefoot. Supposedly, the natural running style has a lower risk of injury and is faster. Sources related to natural running, barefoot running, Pose method, and ChiRunning provide more details about this way of running.
Some controversy surrounds minimalist shoes; proponents say they prevent injuries and solve existing problems with foot development, so that one needs no orthotics, anti-pronation shoes and the like any more. Foot doctors, on the other hand, tend to deem these shoes only suitable for people with perfectly neutral healthy feet without deviations (so, for as good as no one). I have no idea which is true.
Two aspects and their respective advantages can be identified:
The advantage of "zero drop" lies in the fact that, after landing on the ball of the foot, one can lower the heel toward the ground until it touches the latter lightly, and in this movement, the force of striking the ground is absorbed by muscles and tendons in an eccentric contraction, mostly the calf muscle and achilles tendon. With conventional running shoes with raised heels, this is not possible because the heel cushion is in the way, preventing one's heel from sinking and ankle from bending. The natural manner of shock absorption thus employed also evokes a spring reflex in the muscles and tendons, so that one bounces back as it were, receiving a kind of free energy that makes running more efficient and therefore faster. And, using natural shock absorption (muscles and tendons) means that less cushioning in the shoe sole is needed.
An advantage of having a thin sole without much cushioning is that one's ankle is less likely to bend inward ("pronation") or outward ("supination"). There is simply less room for that, and there is less or no risk that the sole will bed down over time on the inside (with pronation) or outside (with supination), which would worsen the problem. Another advantage, to some, is that with thin soles one feels the terrain better so that the experience comes closer to barefoot running. Also, thin soles bend easier under the ball of the foot.
After doing part of my running on different types of minimalist shoes for a few years, I find that the "zero drop" aspect is a definite improvement over conventional running shoes, and relatively easy to get used to. The calf muscle and achilles tendon need some months to adapt. Then, one feels more leverage and spring action in the feet and legs. Running in shoes with raised heels becomes a bit annoying because they block the heel and make it impossible to execute the proper running style.
Harder, in my case, is adapting to little or no shock absorption and thin soles. Two serious problems occur:
Positive impressions I have concerning the knee and achilles tendon; strain on the knee seems to be less in this style of running, though by no means zero. And while the achilles tendon and calf muscle have it harder initially, in the long run the tendon holds out well. This may partly be through adaptation, but I believe it is also because of less sideways movement of the foot and ankle (outward bending in this case). The cause of my achilles problems has always been that the left foot develops over the little toe, and with a natural running style, that occurs to a lesser extent.
Shoes with heel and forefoot at the same height are relatively easy to get used to and seem to allow for more efficient and faster running. I consider the concept of raised heels outdated and would avoid them completely if possible.
In my situation — striving to run fast and having problems adapting to the thin soles and lack of shock absorption of most minimalist shoes — I would be best off with "zero drop" shoes that have a reasonable amount of shock absorption, perhaps with soles of about 15-20 mm thick. Unfortunately, exactly such shoe designs are rare and hard to find; I can see on the Internet they exist, but have not found them for affordable prices yet. So in practice I alternate conventional running shoes with minimalist shoes that have too little shock absorption for me. If I only ran slowly, I think I would have adapted to thin-soled shoes by now. It is the faster running and desire to do well in races that stand in the way of this adaptation. I am not certain if full adaption will eventually succeed, and will evaluate the matter again in a few years.