Part Shoe, Part You: Understanding What Running Shoes Do to Your Form

Running shoe research is a black box to some degree. Researchers put the shoe on a runner’s foot and have them run. Then, we measure some things while they run; oxygen consumption, joint angles, sense of effort– you get the idea. In one sense, you can still argue that the results of this kind of research is useful and well controlled. Through a different lens, by changing the shoe, we’ve actually changed several things at once. Midsole foam compliance (meaning how soft the shoe cushion is), stack height (how tall the shoe stands off the ground), and offset (height difference between the heel and toe) are just a few of the variables altered every time we change a shoe. What we observe in the study is the aggregate result on the runner of several pieces, all at once.The problem is that if multiple things are changing with the shoe all at once, we can’t be certain what effect each individual feature has, or how those features interact with each other, to influence the runner. 

There’s also another problem. One of the large challenges of footwear research is the substantial inherent variability that exists between one person and the next. For example, the early forms of super shoes don’t improve everyone’s running economy equally. Some runners saw 5% benefit while others only saw 1-2% improvement. 

A recent paper by Mark Connick and Gary Lichtwark in the Journal of Applied Biomechanics proposes one way to think more clearly about what might be going on inside the black box. 

It’s part shoe, part you.

If your running economy is suddenly 5% better when you put a special new shoe on, history shows that we’re likely to attribute the change to the shoe. This is partially true, but also not entirely, because it’s still you who’s doing the running. That’s the heart of the framework proposed by Connick and colleagues. They argue that any time we put a shoe on our foot, several things happen that fall into two major categories: what they call shoe-mediated and biomechanically mediated effects. 

A visual model for separating two simultaneous effects of a running shoe on running economy (and by extension, performance). Arrow A represents direct improvement of the shoe in saving energy. Arrow B is how the shoe prompts the runner to change in a way that may also save energy. All researchers currently observe with their study designs is the sum of both A and B, making it hard to know which contributes more or less. Figure from Connick & Lichtwark 2025

If you consider the special foam universally used in super shoes, called PEBA foam, we can see the difference. Traditional running shoes use a different foam, and relative to that foam, PEBA is lighter and springier. Springier, meaning that when we compress PEBA foam, it springs back to its original shape faster. What that means for the runner wearing it is that the shoe captures and returns energy to the runner better than traditional (EVA-based) foams. That’s the shoe-mediated effect.

The second effect– the biomechanically mediated one– depends on both runner and shoe. When a runner switches from a traditional shoe to a PEBA running shoe, perhaps their body operates differently. Maybe the muscles in their calves can store more elastic energy, or maybe they can open their stride up so that each step covers a little more ground. The shoe was necessary for those mechanical changes to occur in how the runner moves, but the changes that led to better performance happened within the runner.

What it means, going back to our original 5% improvement in running economy with the special new shoe, is that part of that 5% is probably coming from shoe-mediated improvements, and part of it is probably coming from biomechanically mediated improvements. All we see in the lab testing is the cumulative 5%, and we don’t know how we got there from a combination of those two mediators. What if the reason that some runners see less gains from a super shoe than others is because the changes to their running stride are less pronounced, or even counter-productive?

There are practical challenges to opening the black box

The challenge is that it’s near a practical impossibility to separate the biomechanical and shoe mediated effects from one another, because any time we change something in the shoe, both the shoe and the runner change. 

One thing we do know is that higher stack height, more cushioned running shoes do appear to prompt runners to make longer strides and have a longer ground contact time with each step. We’ve observed that through motion capture and other video in multiple studies (just a few here, here, and here). That gives us the resulting change in movement, or the output. 

We’re also able to watch the electrical signals in the muscles of the calf through electromyography, and that tells us to what extent an electrical signal is initiating a muscle to contract–part of the input. The problem is that the elastic tissue stretch that’s key to improved running economy wouldn’t yield electrical activity. We’re blind to half of the input, including some of the changes that are likely to matter most.

Can you unlock a shoe’s ability by changing your stride?

The Connick framework has implications for how athletes select their shoes and train their bodies. We need to be able to parse direct shoe effects and biomechanical ones. For performance, and for injury mitigation. 

If we can do that, we can start looking for optimal combinations and working towards them in parallel. On the shoe design side, footwear is already moving towards more customized options with gait-testing and underfoot pressure mapping in your local running shoe store. When I was working at Boulder Running Company all the way back in 2019, Superfeet was already piloting their custom orthotic product offering using these tools. On the biomechanics side, runners frequently pursue changes and improvements to their form, again both for better performance and to stave off possible injury. Could we see a world where runners are also training new gait patterns in order to maximize the gains from the running shoe they have on their foot? It’s all speculation right now, but the implications of a breakthrough in research technique run deep. 

For now, at least we can ponder how the shoe we choose for each run is changing our stride.

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