RUNNING SHOE MODEL PAVES WAY FOR SPORTS EQUITY
A new model will help athletic shoe designers predict how shoes will perform in action.
Written by Nancy Kristof
MIT engineers have developed a model that predicts the optimal running shoe design for a given runner. Pictured is a researcher holding a 3-D-printed midsole, designed based on the model’s predictions. Photo: Melanie Gonick, MIT
ENGINEERING PROFESSOR SARAH FAY draws on her experience as an athlete in her daily work. She’s a biomechanical engineer and the lead author of a study presenting model-based methods for predicting the energetic cost of running in athletic shoes of varying materials and geometry.
Published in 2024 in the Journal of Biomechanical Engineering, the aim of the study is to create a model that can predict how a runner will run in a new shoe design. The work is driven, in part, by athletic gear companies interested in possibilities from 3D printed shoe components such as a sole, but Fay and her team are also excited about the possibilities it may provide for building equity in sports.
“Sports have provided a lot to my life, personally, in terms of my growth and confidence and learning how to work on a team. I think that everybody should have access and be able to play them,” she said. Shoe and apparel design has traditionally been based on the male body, Fay continued. What works for men isn't always appropriate for female athletes.
“That's one of the factors that contributes to the ACL tearing epidemic and women's soccer and women's basketball,” she added. “I think that we can do better, and redesign shoes based on data of women and with female bodies in mind.”
Shifting to model-based evaluation makes it easier to explore new materials and geometries made possible by 3D printing. Traditional evaluation of shoe performance by measuring the metabolic energy expended by human subjects running in the shoes takes time, involves specialized and expensive equipment, and requires large numbers of participants to draw significant conclusions.
Researchers measure the stiffness of midsole designs using an Instron machine to mimic footsteps. Photo: Melanie Gonick, MIT
Most athletic shoes made today rely on a foam sole. Foam is uniform in behavior and the only way to control it is by changing its thickness, Fay said.
“Including 3D-printed technology in the shoes gives us the capability to make shoes with much more interesting properties than just a slab of foam,” she said. Geometry can be tailored, which in addition to the material, can also affect stiffness or bounce, and this is where the model adds value.
“The geometry coupled with the underlying material, translates to the actual macroscopic properties of the shoe,” Fay continued.
The study was produced while Fay was working in MIT’s Sports Lab and the Institute for Data, Systems, and Society (IDSS) with Anette “Peko” Hosoi, professor of mechanical engineering at MIT.
“The biggest challenge is the fact that it's hard to know what humans are doing, so we can understand the material properties of the shoe, but that doesn't mean that we know how a person will respond when they put that shoe on,” she said.
“Including 3D printed technology in the shoes gives us the capability to make shoes with much more interesting properties than just a slab of foam.”
Sarah Fay, assistant professor, Picker Engineering Program, Smith College
The simplified two-dimensional mechanical model learns from real public datasets of running gaits and chooses from them via a process called inverse optimal control. The team used their model to simulate each runner’s gait multiple times. By programming the model to assume different the “biological cost” of conditions, such as the degree to which a leg swings or the impact on the treadmill, they could compare the modeled gait with the runner’s actual gait to see which matched. The results showed most runners tend to minimize two costs: the impact their feet make with the treadmill and the amount of energy their legs expend.
The results also showed that in general, shoes must be dramatically different to produce measurable and significant differences in performance. With the study complete, Fay has moved on to Smith College, where she’s starting a new research lab. Her goal is to continue to work in the sports engineering space and aims to focus on engineering products that promote inclusion and accessibility in sports.
“Working with people is exciting because it's taking really, really complex systems and trying to distill it down into really simple physical models,” she said. “Things are unpredictable, so there's always more to learn about how we're interacting with the world.”
Nancy Kristof is a technology writer in Denver.
© 2025 The American Society of Mechanical Engineers. All rights reserved.