Finding the right shoe is crucial for runners, whether they are seasoned athletes or just starting out. However, each runner is different, and what works for one person may not work for another. Unfortunately, there is no simple solution to determine the perfect shoe for an individual's specific running style, other than trying on various options.
MIT engineers are looking to transform this situation by developing a fresh framework that anticipates the impact of specific shoe characteristics on a runner's performance.
The basic design includes a person's height, weight and overall measurements, as well as shoe attributes like rigidity and bounce in the middle sole. Using this information, the design then replicates a person's running style, or how they would run, in a specific shoe.
By utilizing the model, the scientists have the ability to replicate the alterations in a runner's stride when wearing various types of shoes. Subsequently, they can select the shoe that yields the optimal results, as determined by the extent to which a runner's energy expenditure is minimized.
The current model is effective in replicating variations in a runner's stride when comparing two highly distinct shoe styles. However, it is not as precise when assessing moderately similar designs, such as the majority of running shoes available in the market. As a result, the researchers suggest that this model would be most beneficial for shoe designers seeking to explore innovative concepts in sneaker design.
"Shoe designers are starting to 3D print shoes, meaning they can now make them with a much wider range of properties than with just a regular slab of foam. Our model could help them design really novel shoes that are also high-performing." - Sarah Fay, a postdoc in MIT’s Sports Lab and the Institute for Data, Systems, and Society (IDSS)
The team has aspirations to enhance the model, with the aim of enabling consumers to eventually utilize a comparable version to select shoes that suit their individual running style.
"We've allowed for enough flexibility in the model that it can be used to design custom shoes and understand different individual behaviors. Way down the road, we imagine that if you send us a video of yourself running, we could 3D print the shoe that’s right for you. That would be the moonshot." - Fay
The Journal of Biomechanical Engineering recently published a study unveiling the fresh model. The study was written by Fay and Anette "Peko" Hosoi, a mechanical engineering professor at MIT.
Shocking Revelation
The team developed their latest prototype after consulting with partners in the sneaker business, who have recently begun producing 3D-printed footwear on a large scale. These innovative designs feature midsoles created through 3D printing, which resemble complex support structures. These structures can be customized to provide targeted levels of flexibility or rigidity in various areas of the sole.
"With 3D printing, designers can tune everything about the material response locally. And they came to us and essentially said, 'We can do all these things. What should we do?'" - Hosoi, a mechanical engineering professor at MIT
"Part of the design problem is to predict what a runner will do when you put an entirely new shoe on them. You have to couple the dynamics of the runner with the properties of the shoe." - Fay
Fay and Hosoi initially sought to depict the mechanics of a runner by employing a basic framework. They took inspiration from Thomas McMahon, a prominent scholar in the field of biomechanics at Harvard University. In the 1970s, McMahon utilized a straightforward "spring and damper" model to simulate the fundamental gait mechanics of a runner. By employing this gait model, he made projections on the potential speed of a person running on different types of tracks, ranging from traditional concrete surfaces to more elastic materials. The model indicated that runners would likely achieve higher speeds on tracks that were softer and provided a supportive environment for their natural gait.
While it may not come as a shock in modern times, this revelation was quite groundbreaking back then. As a result, Harvard decided to make significant changes to its indoor track. The modifications proved to be successful as runners started to break records due to the track's softer and bouncier surface, allowing them to run at a much faster pace.
"McMahon's work showed that, even if we don't model every single limb and muscle and component of the human body, we’re still able to create meaningful insights in terms of how we design for athletic performance." - Fay
Biological Cost Function
Influenced by McMahon's ideas, Fay and Hosoi created a comparable and simplified version of a runner's mechanics. Their model portrays a runner as a focal point of weight, featuring a rotating hip and an extending leg. The leg is connected to a shoe resembling a box, which can be adjusted for both vertical and horizontal springiness and shock absorption.
They came to the conclusion that it would be possible to enter a person's fundamental measurements, like their height, weight, and leg length, into the model. Additionally, they could input the shoe's material characteristics, such as the rigidity of the front and back midsole. By doing so, they could utilize the model to simulate how a person would most likely walk or run in that particular shoe.
However, they also came to the realization that an individual's way of walking can be influenced by a less tangible characteristic known as the "biological cost function". This aspect may not be consciously recognized by a runner, yet they may unconsciously attempt to minimize it during their runs. The researchers hypothesized that if they could identify a universal biological cost function among most runners, they could not only predict a person's walking style with a specific shoe but also determine which shoe would result in the most optimal running performance.
Taking this into consideration, the team referred to a prior study conducted on treadmills. This study extensively measured various aspects of runners, including the impact force of their steps, the movement and angle of their joints, the elasticity of their strides, and the exertion of their muscles while running, all while wearing the same kind of running shoes.
Fay and Hosoi had a theory that the way each runner moved was not only influenced by their physical attributes and the shoes they wore, but also by an unconscious desire to minimize certain biological factors that are currently unknown.
In order to uncover these factors, the team used their model to simulate the running style of each runner multiple times. Each simulation was programmed to assume that the runner was minimizing a different biological cost, such as the amount their leg swung or the impact they made on the treadmill. The team then compared the simulated running style with the actual running style of the runner to determine which simulation matched the real thing and therefore, which biological cost was being minimized.
Ultimately, the team discovered that the majority of runners have a tendency to reduce two expenses:
- the force of their feet on the treadmill
- the energy exerted by their legs
"If we tell our model, 'Optimize your gait on these two things,' it gives us really realistic-looking gaits that best match the data we have. This gives us confidence that the model can predict how people will actually run, even if we change their shoe." - Fay
In the last phase, the scientists replicated various shoe designs and employed the model to anticipate a runner's stride and the effectiveness of each stride in relation to a specific shoe style.
"In some ways, this gives you a quantitative way to design a shoe for a 10K versus a marathon shoe. Designers have an intuitive sense for that. But now we have a mathematical understanding that we hope designers can use as a tool to kickstart new ideas." - Hosoi
By the way, adidas has provided partial support for this research project.