Physics and the Vimazi "Forces in Running" Study

Physics and the Vimazi "Forces in Running" Study

Being lifelong marathoners here at Vimazi, we’ve long searched for the best running shoe. You can probably relate. In 2018, after years working for other running footwear brands, we created Vimazi with the idea of designing and making the best running shoe. 

But what the heck does “best running shoe” even mean? Back in 2017, we had a brainstorm in this regard: If you tuned shoes by pace zone, you could make them more efficient. That was the theory. Given our deep background in math and physics, we knew a scientific understanding of running forces was necessary. 


Time passes and several years of intensive physics computations later, we’d built an equation that allowed us to calculate the exact forces generated in the heel, arch, forefoot, and big toe at any running paces. This new theory of running forces was consistent with Newtonian physics (more on that it a second).

Two things surprised us: First, the impact force occurs and ends so quickly that it can’t help with propulsion. Second, the propulsion force is much greater than the impact force. Check out this chart.

As crazy as it sounds, this had never been done before.

Wait, running shoes have been studied for forever, haven’t they? Yes! Let’s discuss. Countless observational studies have seemed to show that super shoes help runners run faster. Unfortunately, these observational studies all suffer from a causation fallacy—we observe runners running faster, therefore it must be because of the shoes. But there's no direct link from shoes to better performances. Even the academics running the studies say they don't know!

Faster running could result from smarter training techniques, better fueling during events, advancements in diet and hydration, or just more runners? Some of the studies suffered from self-reporting bias as well, which isn’t reliable and isn’t even actual science. Worse, most of the studies and descriptions of running and running shoes haven’t conformed with basic Newtonian physics. Last I heard we’re all still running on earth…but I digress.

We took our new theory of running forces and verified it with the experimental data from our Forces in Running Study which looked at the timing, location, and intensity of forces generated while running. The research looked at a variety of paces, footstrike patterns, and runner weights for both women and men.

We also found that midsole foams can’t accommodate the wide range of forces. Using a dynamic compression device to test the compression constant in the heel and forefoot of various shoes, we found that midsole foam (it doesn’t matter what type) isn’t nearly as adaptable as we’ve all been led to believe. In fact, it turns out that it’s impossible for one density of midsole foam to respond appropriately and efficiently to a wide range of forces. 

Two things became clear. First, given the physics and study data, that the midsole shouldn’t be thought of as one homogenous unit. To make a shoe that works in concert with the physics of running—in other words, a best running shoe—you need to think about the heel and forefoot as completely separate functional areas. Our solution was to invent a foam disc we call a forefoot FastPod that responds to the forces you generate during push-off. (The heel and midfoot area are tuned to react to the impact force of a given pace zone.)

Second, we learned that runners generate a wider range of both impact forces and propulsion forces than we had thought. Those forces are intense at 5 minutes per mile (3:06 min/km) but much more gentle at 12 minutes per mile (7:27 min/km).

This means running shoes need to be tuned between heel and forefoot as well as by pace. When we adjust the density of the foam in the heel and midfoot differently from the forefoot FastPod for each of our running shoe models, we’re matching the compression constant with the forces inherent within a specific pace zone. We call this density adjustment “tuning.” 

Here's the problem: The midsole density of most running shoes is the same from heel to toe. This means while you may get fine cushioning, you’ll necessarily get a mushy, inefficient push off. If you get an efficient push off, you won’t get the full amount of cushioning you deserve.

It’s been a long haul to develop pace-tuned shoes, but pursuing the truth and understanding the physics paid off. By tuning midsole foam density between heel and forefoot as well as by pace zone for each of our models, we’ve been able to optimize cushioning and maximize push-off efficiency for every runner. Vimazi running shoes are more personalized than any other shoe out there. 

Vimazi's FastPod solution: To give runners optimized cushioning while also ensuring they get the most efficient push-off possible, we created a our forefoot FastPod (red disc). The heel and arch area are tuned to respond to the forces you generate on impact, reducing shock. The FastPod is tuned to react to your propulsion forces so your push-off is as efficient as possible. Each of models has been tuned differently to accommodate the forces that occur in that model's pace zone. 

Vimazi Z70 midsole showing FastPod

Developing this midsole was much more difficult than it looks. First, we had to solve the physics. Not an easy task! Then we had to find a midsole manufacturer that would deliver foam specced to a very specific durometer. No one's done this before, and most manufacturers said "no." Finally, we had to figure out how the two parts of the midsole would be pressed together in a way that facilitated a smooth, flowing transition from footstrike through toe-off. Perfection doesn't come easy!

Pace-tuning has allowed us to democratize performance for all runners because no matter your pace, you want the best cushioning and most efficiency.

Yes, tuning shoes for a specific pace zone is a radically different way to think about running shoes, but it’s the right way. This work has definitely closed in on our goal of creating the best running shoe. We hope you give them a try.

Of course you’re welcome to continue running in non-tuned shoes with generic cushioning that probably aren’t correctly responding to the forces you generate at your pace. But we think running in a shoe that’s more personalized to the way you run is pretty cool. And if you can get better performance and a more cushioned ride, all the better.


More About Vimazi

Here’s what Vimazi does
We make pace-tuned running shoes that provide better cushioning and more efficiency than previous generations of running shoes.

The physics of pace-tuned shoes
Back in 2017, while Vimazi CEO Scott Tucker was running to his 6am interval workout, he had an idea. A shoe made for a specific pace, he thought, might offer better cushioning and more propulsive efficiency than a generic shoe that wasn’t “tuned” for a particular pace.

It took three years to fully understand the physics of human running, and the forces that are generated. When we finally understood the physics, we built an equation that defines running forces. We’re now able to calculate the exact impact force and propulsion force, in Newtons, for any pace, including variations for height, weight, and cadence. (A Newton is a metric unit of force.) Data from the Forces in Running study we conducted aligned with the force calculations we got from the physics. In other words, we know it works.

Knowing the precise impact and propulsion forces at each pace, allowed us to create shoe models for different pace zones. So our pace-tuned technology is based on pure physics. No hand waving, no conjecture, no correlative studies, no self-reported data sets, no marketing fluff. We started with the physics of human running, and it led us to pace-tuned shoes.

The problem with previous gen running shoes
Most running shoes have the same foam density from heel to toe, and they’re sold to runners of every pace. The trouble is that midsole foam can’t respond correctly to the forces at all paces, and it can’t even respond appropriately to the differences between impact and propulsion forces. To make sure you get all the cushioning you want as well as all the efficiency you deserve, you need a shoe that’s made for a specific pace zone and tuned differently in the heel than the forefoot.

The Vimazi solution
Our solution to this running shoe problem was to create something that's never been done before—pace-tuned running shoes. In 2023, after years of testing, we launched seven road shoe models that span paces from 4:30 minutes per mile to 15 minutes per mile (2:50-9:30 minutes per kilometer). By making a shoe for a specific pace zone, we’ve been able to deliver better impact cushioning and propulsion efficiency for every runner.

25 years experience
We’ve taken everything we learned making running shoes for 25 years—and running marathons for even longer—and elevated it to a whole new level with pace tuning. It offers a better and more personal running experience. We were instrumental in creating shoes for Montrail, Scott Sports, and Pearl Izumi. We learned even more while owning a specialty running store and organizing running events.

A marathoner’s fit
Running shoes can have the best tech, but if they don’t fit well, nobody will wear them. We wouldn’t either! Not only have we spent our careers perfecting innovative fit technologies at other companies, notably at Montrail, we’re also life-long marathon runners ourselves. So we understand fit and know how critical it is, from heel to toe. Each of our models has been painstakingly designed and built with the perfect fit in mind. They’ve also been extensively road tested since 2019, including at the Boston, London, Portland, Missoula, San Antonio, and Two Oceans Marathons. We think you’ll love them.


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