Like many runners, I love shoes and own a lot of them. First of all, it’s important to point out that shoes aren’t that important... Training and nutrition probably have a much bigger impact on your performances but I believe it’s important to look at running performance as a whole and shoes are a part of that big picture.
I totally agree with the idea that humans are born to run. As a species we have evolved to cover long distance on foot in the heat. This mean running slowly on mostly flat terrain for hours on end. What about running down a mountain pass as fast as possible in the end of an ultra or simply running a very fast road marathon time? These are totally different situations. I have myself ran in minimal footwear in the past and I still run with thinner shoes sometimes in training but I could no longer be called a “minimalist runner”. I believe that a more minimal shoe can help some people to run with a higher step frequency and reduce impacts which may prevent injuries and make them more efficient. However, when it comes to performances in mountain ultra marathon, minimal footwear may not be the most appropriate.
Ultra running performance can mostly be improved by minimizing the slowing down happening in the later stage of a race. Therefore, finding the factors that slows you down is key. Everybody’s different and those factors vary from one person to another. Many runners slow down simply because the aren't eating enough during the race but muscle pain can also slow you down. For some it’s the quads who give up first, for others, like me, it’s the calves and feet. If your quads give up on you despite proper downhill training, running in a more minimal footwear could be a good idea to increase your stride rates and reduce the stress on your quads, knee and back. For runners like me, it’s the other way around. I run with a very high step frequency, higher than 180 (approaching 200 in average for a road marathon!). If I race in a more minimal shoe, my feet and Achilles tendons get really sore but my quads are fine. With a more cushioned footwear, I can cross the finish line with my legs totally trashed. Every muscle group equally destroyed. That’s how you optimized performance! Of course shoe weight matters when it comes to running economy but nowadays we can find lightweight cushioned shoes so it’s not really an issue anymore. Thank you Hoka One One!
What I’m trying to say is that everyone has to find it’s own optimal footwear and the distance to run or the runners weight aren’t very important in this decision process. Actually, I think it is more a matter of speed than weight. More cushion for shorter races totally make sense to me. It’s impressive to see the number of people who think body mass as anything to do with the amount of cushioning they need for running. Overweight people are probably better with minimal footwear to prevent getting injured. They may not maximize performance going this way but they have a lot more to gain by losing fat mass first.
As a sport scientist, I have read a lot of papers about running footwear. I first thought about adding references to this post but it would have ended up being a critical review. Most studies on running footwear are done with fresh runners on treadmills. They often conclude that a lighter shoe is better but the conditions of the test are far from what we found in a mountain ultra marathon. There’s also at least one study pointing to a superiority of cushioned shoes for trail running but in this case the subjects weren't used to the minimal footwear tested so it’s hard to agree with their conclusion. There’s definitely room for improvement in this area of research. I’m pretty sure shoe company have a lot of good data but they keep it for themselves. It will be interesting to see what are the specifications of the shoes used in the sub 2 hours marathon attempt announced by Nike.