Time for a bit of a rant, hold on tight.
My Wednesday mornings are typically reserved for Daddy-dates with my 2-year-old son. Sometimes we hang out and play trucks, sometimes we go out on an adventure. Today we decided to hit what he likes to call “the gym” (it’s a gymnastics training center that doubles as a kid playground in the morning). One of my favorite pieces of equipment at the gym is the tumble-track. If you’re not familiar with a tumble-track, it’s basically a long, narrow trampoline that you can run down and leap off of onto a big mat to practice flips (something that I wouldn’t dare try…).
Today I was running down the tumble track and was wondering to myself how it would feel to run a longer distance on the bouncy surface. That got me to thinking about the adidas Boost midsole material, which has been described as “bouncy” and is being touted as providing enhanced energy return over traditional EVA foam. As I ran down the tumble-track I focused intently on what my legs were doing. It feels great to bound down the track, but my legs were behaving very differently than they do when I run out on the road or trail, and it was happening without any need for conscious control. My ankle was locked in extreme dorsiflexion, essentially removing it as a shock absorber, and my knee was locked as well. Basically, my leg joints were locked in place, and I was bouncing along on two very stiff limbs.
That got me to thinking, why didn’t I adopt my usual running form? So, I consciously tried to run as if I were on a road, and it felt horrible! I obviously did not have a respiratory gas analyzer handy (I would have been the coolest, or dorkiest, dad there if I did), but running normally felt terribly inefficient on the extremely soft and bouncy surface of the tumble track.
What does this have to do with the adidas Boost midsole? The lesson from the tumble track is that the human body responds very differently when running on surfaces of different properties. We adapt on the fly based upon sensory feedback coming in from our feet and legs, and we adjust joint angles, limb stiffness, muscle activation, and so on (you can read more on this topic here).
Now watch the adidas Boost teaser video:
Why does this bother me so much? Well, the human body is not a rigid metal ball, and a video showing a metal ball being dropped onto cushioning tells us very little about how the human body will react to such cushioning.
I was invited by adidas to attend their release event today in New York City for the Boost midsole, but was not able to attend due to other commitments. I instead watched the video of the event on-line, and I was rather disappointed by the entire thing.
Frankly, I’m tired. I’m tired of marketing trumping science. Adidas is making some bold claims about the energy returning properties of Boost, but all I have seen so far is this steel ball video and some references to mechanical testing results. Bold claims require strong evidence – the human body is not a steel ball, and mechanical testing cannot reveal exactly how the human body will respond to a given type of cushioning material. We have muscles, joints, tendons, and ligaments that all work together as we run. I want to know how this cushioning works with this incredible system that is the human body. After all, the shoe is meant to be worn on human feet.
It may be the case that Boost does work, that it does allow runners to shave seconds or perhaps minutes off their marathon time (as an aside, is it even a good thing if the improvement is due to a shoe and not due to hard work?). After all, we do know that tuning surfaces can lead to performance gains and reduction of injury risk (read about the Harvard Track for example).
But where’s the evidence that shelling out $150 for this shoe is worth the risk that it might not work? It wouldn’t be that hard to do a study comparing a Boost shoe to a similar EVA cushioned shoe – get a bunch of runners, and test their oxygen consumption at steady speed in one vs. the other (here’s a post about a study that did exactly this comparing barefoot running to running in racing flats). There are lots of labs out there that can do this. Without this information, buying this shoe is taking a risk – we’re hoping that the energy return provided by the midsole will enhance our performance. However, it’s entirely possible that the response will be much like my experience on the tumble track – my legs may want to stiffen up in order to take advantage of the bouncy surface below. How do legs stiffen? Simple, muscles contract. And when muscles contract it requires ATP, and ATP is the energetic currency of the human body. So I want to know how muscle activation changes in this shoe vs. an EVA shoe, how limb stiffness changes, and whether we actually are more economical when running in it. Without that data all we have is a flashy marketing story.
Let’s look at this from one other angle. Suppose our limbs do stiffen up when we run in Boost. What does this do to force application? What if running economy does improve, but it does so via adoption of a form that causes greater wear and tear on our joints. This is where science is important. This is why we need people looking at how footwear influences injury risk. This is why we need science to back up marketing claims made about shoes. Either that, or stop making marketing claims that don’t tell the whole story (with the key piece of that story being how the shoe affects us when it’s on our feet). If adidas had simply come out and said they have a cool new midsole material that feels really different and let word of mouth do its thing, I would never have written this post. But specific claims about energy returning properties of the midsole material have been made, and I want more answers, especially for a shoe with a $150 price tag.
Boost may be great. Adidas may have created a revolutionary product. I even asked one of my contacts at adidas several weeks ago about trying it to evaluate for myself. My beef is not with the shoe per se, it’s with the marketing. I want evidence to come along with the marketing claims, and I didn’t see any of that today. Perhaps evidence of benefit exists, perhaps not, but I remain a skeptic without it.