Posted on Jul 15

Millimeters and Midfoot Strike

Millimeters and Midfoot Strike

Anton Krupicka running on a Sports Research Lab treadmill: TenBroek: "We set up to capture motion capture data on his gait. Kyle Skaggs is awaiting his turn in the background also. We can capture how these guys move in a typical product and then see how they move in something like the NB Minimus."

Trampas TenBroek spends his days contemplating, and calculating, the implications of millimeters. Here, in the New Balance Sports Research Lab, where a team with backgrounds in mechanical engineering, anatomy, biomechanics and physics is gleaning new sets of insights about the way in which we run, small measurements have enormous implications. In the development of NB Minimus, for which the 4mm heel-to-midfoot drop has been a source of significant discussion both inside and outside of New Balance, the work of the Sports Research Lab has been a study in both the way our bodies behave, and the ways in which our shoes change that behavior.

As it turns out, these millimeters have a profound impact on the way in which we think about designing a shoe.

"The shoe industry and biomechanics community have believed for years that large loading rates (the measure of the speed and force with which a runner strikes the ground) are detrimental to the body," says TenBroek. "This is why we put a lot of cushioned foam in most trainers. This foam reduces the loading rates at impact compared to landing the same way with less-cushioned materials."

The recent interest in minimalist running — and a critical part of the development of NB Minimus — is connected to the increase in discussion about the virtues of midfoot striking. This technique represents a significant change in the way many runners, accustomed to striking on the heavily-cushioned heel, approach their form. The Sports Research Lab team viewed the use of NB Minimus as working hand-in-hand with an ongoing transition to midfoot striking — a process that was part product design and part form.

"We also know changing other things about the way your run can reduce these loading rates, such as taking smaller steps and utilizing other joints," said TenBroek. "It turns out that running on the midfoot encourages this approach. Therefore you can get away with less material underfoot, if you change some things about the way you run."

The foundation for these conclusions lies in the lab itself — a collection of gear (and gearheads) on the lower levels of New Balance's design offices in Lawrence, Massachusetts. Here, the team puts a range of runners through their paces, on a treadmill surrounded by high-speed cameras capturing every muscle twitch and turn, over a glass force plate implanted with piezoelectric crystals that capture the minute directional forces in a runner's strike. The Sports Research Lab team understands the ways in which we all run, in far more precise terms than most of us do.

"The problem is that it is difficult for most to change the way they run a great deal. With this in mind, we wanted to make sure we had enough material under the heel for most of these people. This helped drive how thick the heel of the NB Minimus would be."

The mechanics of midfoot striking have implications for product development, though, that extend beyond simply reducing the material under the heel, and lowering the profile of the shoe.

"Reducing underfoot material almost always requires the body to change the way it runs — likely moving towards a midfoot strike and shorter steps" says TenBroek.

The work of the Sports Research Lab team becomes far more difficult to quantify and measure when it comes to understanding what runners feel — and turning that feedback into insights that drive the development of a shoe like NB Minimus. The team tested extensively each iteration of the NB Minimus prototypes — from recreational runners to elite ultramarathoners like Tony Krupicka and Kyle Skaggs, whose insights and ideas had driven much of the initial thinking behind the shoes.

"The design input that I've had in the [NB] Minimus and the 101 is really an outgrowth of the modifications I've made to my shoes in the past — especially in [NB] Minimus where it's down to a 4mm drop between the heel and forefoot. It's really close to a shoe that I'm 100% comfortable in and don't need to do any modifications to. That's super exciting — to go from shoes that I feel the need to carve up to 'BOOM': just being able to take a shoe that I helped design out of the box, put it on my foot and go running."

-Tony Krupicka in Return to Leadville

"Through our wear testing and the people we had in the lab running in the product we created with varying drops and midsole thicknesses, we learned that going from a 10-12mm drop, which the vast majority of trainers are, to nothing or very little drop can lead to some pretty significant soreness. That isn't to say that "some" soreness isn't normal and likely not damaging for most; however, there is a point where soreness is not good soreness or harmless soreness and it is often difficult for people to know the difference" says TenBroek. "Runners did eventually acclimate to the changes in drop but more drop takes longer to acclimate to. The 4mm drop yielded the preferred ride of the heights that were tested."

While the 4mm drop represents the ideal specification for runners making the transition to a closer-to-barefoot experience, the work of the Sports Research Lab on NB Minimus is far from complete. New Balance is continually gathering feedback, both inside and outside of the lab, which will shape the next round of NB Minimus shoes.

Glossary

Drop:

'Drop' is the difference between heel height and toe height. All NB Minimus shoes have a 4mm drop which provides a more neutral foot position than traditional shoes (which average a 12mm drop).

What loading rates look like:

The data from the in-shoe pressure system used in the New Balance Sports Research Lab can be converted to three dimensional animations of the runner's strike, illustrating the impact on the runner's foot through the stride.

The force plate:

A glass plate mounted on a concrete and steel structure and made with piezoelectric crystals, measures a runner's force in three directions: left-to-right, forward-to-back, and vertically.

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