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    New model predicts how shoe properties affect a runner’s performance

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    A good shoe can make a huge difference for runners, from career marathoners to couch-to-5K first-timers. But every runner is unique, and a shoe that works for one might trip up another. Outside of trying on a rack of different designs, there’s no quick and easy way to know which shoe best suits a person’s particular running style.

    MIT engineers are hoping to change that with a new model that predicts how certain shoe properties will affect a runner’s performance.

    The simple model incorporates a person’s height, weight, and other general dimensions, along with shoe properties such as stiffness and springiness along the midsole. With this input, the model then simulates a person’s running gait, or how they would run, in a particular shoe.

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    Using the model, the researchers can simulate how a runner’s gait changes with different shoe types. They can then pick out the shoe that produces the best performance, which they define as the degree to which a runner’s expended energy is minimized.

    While the model can accurately simulate changes in a runner’s gait when comparing two very different shoe types, it is less discerning when comparing relatively similar designs, including most commercially available running shoes. For this reason, the researchers envision the current model would be best used as a tool for shoe designers looking to push the boundaries of 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,” says Sarah Fay, a postdoc in MIT’s Sports Lab and the Institute for Data, Systems, and Society (IDSS). “Our model could help them design really novel shoes that are also high-performing.”

    The team is planning to improve the model, in hopes that consumers can one day use a similar version to pick shoes that fit their personal 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,” Fay says. “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.”

    The new model is reported in a study appearing this month in the Journal of Biomechanical Engineering. The study is authored by Fay and Anette “Peko” Hosoi, professor of mechanical engineering at MIT.

    Running, revamped

    The team’s new model grew out of talks with collaborators in the sneaker industry, where designers have started to 3D print shoes at commercial scale. These designs incorporate 3D-printed midsoles that resemble intricate scaffolds, the geometry of which can be tailored to give a certain bounce or stiffness in specific locations across the sole.

    “With 3D printing, designers can tune everything about the material response locally,” Hosoi says. “And they came to us and essentially said, ‘We can do all these things. What should we do?’”

    “Part of the design problem is to predict what a runner will do when you put an entirely new shoe on them,” Fay adds. “You have to couple the dynamics of the runner with the properties of the shoe.”

    Fay and Hosoi looked first to represent a runner’s dynamics using a simple model. They drew inspiration from Thomas McMahon, a leader in the study of biomechanics at Harvard University, who in the 1970s used a very simple “spring and damper” model to model a runner’s essential gait mechanics. Using this gait model, he predicted how fast a person could run on various track types, from traditional concrete surfaces to more rubbery material. The model showed that runners should run faster on softer, bouncier tracks that supported a runner’s natural gait.

    Though this may be unsurprising today, the insight was a revelation at the time, prompting Harvard to revamp its indoor track — a move that quickly accumulated track records, as runners found they could run much faster on the softier, springier surface.

    “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 says.

    Gait cost

    Following McMahon’s lead, Fay and Hosoi developed a similar, simplified model of a runner’s dynamics. The model represents a runner as a center of mass, with a hip that can rotate and a leg that can stretch. The leg is connected to a box-like shoe, with springiness and shock absorption that can be tuned, both vertically and horizontally.

    They reasoned that they should be able to input into the model a person’s basic dimensions, such as their height, weight, and leg length, along with a shoe’s material properties, such as the stiffness of the front and back midsole, and use the model to simulate what a person’s gait is likely to be when running in that shoe.

    But they also realized that a person’s gait can depend on a less definable property, which they call the “biological cost function” — a quality that a runner might not consciously be aware of but nevertheless may try to minimize whenever they run. The team reasoned that if they can identify a biological cost function that is general to most runners, then they might predict not only a person’s gait for a given shoe but also which shoe produces the gait corresponding to the best running performance.

    With this in mind, the team looked to a previous treadmill study, which recorded detailed measurements of runners, such as the force of their impacts, the angle and motion of their joints, the spring in their steps, and the work of their muscles as they ran, each in the same type of running shoe.

    Fay and Hosoi hypothesized that each runner’s actual gait arose not only from their personal dimensions and shoe properties, but also a subconscious goal to minimize one or more biological measures, yet unknown. To reveal these measures, the team used their model to simulate each runner’s gait multiple times. Each time, they programmed the model to assume the runner minimized a different biological cost, such as the degree to which they swing their leg or the impact that they make with the treadmill. They then compared the modeled gait with the runner’s actual gait to see which modeled gait — and assumed cost — matched the actual gait.

    In the end, the team found that most runners tend to minimize two costs: the impact their feet make with the treadmill and the amount of energy their legs expend.

    “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,” Fay explains. “This gives us confidence that the model can predict how people will actually run, even if we change their shoe.”

    As a final step, the researchers simulated a wide range of shoe styles and used the model to predict a runner’s gait and how efficient each gait would be for a given type of shoe.

    “In some ways, this gives you a quantitative way to design a shoe for a 10K versus a marathon shoe,” Hosoi says. “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.”

    This research is supported, in part, by adidas. More

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      in Data Management & Statistics

      Building a playbook for elite-level sports

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      “All I did was swim,” says Jerry Lu, recalling his teenage years as a competitive swimmer. “From age 12 to 19, it was close to 30 hours a week of training.” Although Lu no longer competes himself, his understanding of the dedication and impeccable technique required in elite sports continues to shape his path as a master’s student at the MIT Sloan School of Management.

      As an undergraduate at the University of Virginia, Lu majored in systems and information engineering and economics. He had stopped swimming competitively, but he stayed connected to the sport as a technical performance consultant for the university’s nationally ranked swim team. Under his advisor, Ken Ono, Lu built a methodology of analyzing data from sensors worn by swimmers to improve their individual performance. By looking at an athlete’s propulsion and drag data over the course of a race, Lu can advise them on where they can shave off tenths of a second simply by adjusting their stroke to be more efficient.

      That experience inspired Lu to pursue a career in other aspects of sports. At MIT he’s pursuing a master’s in finance to build the analytical skills necessary to enable the sustainability of sports that don’t already enjoy the major commercial success of, say, football or basketball. It’s especially a challenge for Olympic sports, such as swimming, which struggle for commercial ventures outside of Olympic years.

      “My work in swimming is focused on athlete performance to win, but the definition of winning is different for a sport as a whole, and for an organization,” Lu says. “Not only do you need to win medals, a big part of it is how you allocate money because you also need to grow your sport.”

      At MIT, Lu is building a playbook for high-performance sports from both an athletic and financial perspective. He’s been gaining exposure to additional elite sports by working with MIT’s Sports Lab under Professor Anette “Peko” Hosoi. His work there isn’t a requirement for his master’s program, but Lu appreciates that the program’s flexibility allows him time to pursue research that interests him, alongside the required curriculum.

      “I’m quite lucky to be here in the sense that MIT is known to train great people in engineering,  science, or business, but also people with unique passions,” says Lu. “People that love football drafting, people that love to understand how you throw a curveball — they use their knowledge in very unexpected ways, and that’s when innovation happens.”

      Lu’s research with the Sports Lab focuses on optimizing strategies for aesthetic sports, such as figure skating or snowboarding, which are judged very differently than swimming is. Instead of figuring out how to move faster, athletes are interested in structuring routines that net them the most points from a panel of judges. Modelling techniques can be helpful for figuring out how to put together routines to maximize an athlete’s abilities, and also to predict how a judge might assign points based on how or when a skill is demonstrated. Optimizing both athletic performance and judge psychology is a challenge, it’s this type of innovation that excites him. He hopes more sporting organizations will adopt similar data-driven strategies in the future.

      When asked where he’d like to end up after finishing his degree, “The sport industry is the natural choice,” Lu says. Though he is certain his career will lead to sports eventually, he is still open to exploring new paths. This summer he will be a trading intern at Citadel Securities to apply the concepts learned in his degree program courses. He’s also picked up sailing since coming to MIT, already reaching the highest amateur rating in under a year. Lu consistently strives for excellence, whether in himself or for those he works with.

      Since graduating from UVA, Lu has continued to work with swimmers, including national champions and Olympic medalists, as a technical performance consultant. He’s also branched out into another Olympic sport, triathlon. Lu describes it as a side gig, but he’s deeply invested in the athletes he works with, even taking trips to the Olympic Training Center to collect data and help them build strategies for improvement.

      “The most fun part is actually interacting with the athletes and engaging and understanding how they think,” says Lu. “It’s easier for me to do so than others, because if you’ve never swam before and you’ve never trained as an elite athlete before, it’s hard to understand what exactly you can and cannot do and how to communicate these things to a coach or an athlete.” More

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      in Data Management & Statistics

      Lockdowns reveal inequities in opportunities for walking activities

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      Lockdowns saved lives during the global SARS-CoV-2 pandemic. But as much as they have slowed the spread of Covid-19, there have been some unintended consequences.

      New MIT research shows that lockdowns in 10 metropolitan areas throughout the United States led to a marked reduction in walking. These decreases were mostly seen among residents living in lower-income areas of the city, effectively reducing access to physical activity for minorities and people suffering from illnesses such as obesity and diabetes.

      “Walking is the cheapest, most accessible physical exercise that you can do,” says Esteban Moro, visiting research scientist in the MIT Connection Science Group and senior author on the Nature Communications paper published on June 16. “Places in which people have lower incomes, less park access, and more obesity prevalence were more affected by this walking reduction — which you can think of as another pandemic, the lack of access to affordable exercise.”

      The research focused on recreational versus utilitarian walking done by residents in the U.S. cities of New York, Los Angeles, Chicago, Boston, Miami, Dallas, San Francisco, Seattle, Philadelphia, and Washington D.C. (Utilitarian walking is defined as having a goal; for example, walking to the store or to public transportation. Recreational walking is a walk meant for leisure or exercise.)

      Comparing cellphone data from February 2020 to different time points throughout 2020 lockdowns, the researchers saw an average 70 percent decrease in the number of walks — which remained down by about 18 percent after loosened restrictions — a 50 percent decrease in distance walked, and a 72 percent decrease in utilitarian walking — which remained down by 39 percent even after restrictions were lifted.

      On their face, these findings may not be surprising. When people couldn’t leave their homes, they walked less. But digging deeper into the data yields troubling insights. For example, people in lower-income regions are more likely to rely on public transportation. Lockdowns cut back on those services, meaning fewer people walking to trains and buses.

      Another statistic showed that people in higher-income areas reduced their number of utilitarian walks but were able to replace some of the lost movement with recreational walks around their neighborhoods or in nearby parks.

      “People in higher-income areas generally not only have a park nearby, but also have jobs that give them a degree of flexibility. Jobs that permit them to take a break and walk,” says Moro. “People in the low-income regions often don’t have the ability, the opportunity or even the facilities to actually do this.”

      How it was done

      The researchers used de-identified mobile data obtained through a partnership within the company Cuebiq’s Data for Good COVID-19 Collaborative program. The completely anonymized dataset consisted of GPS locations gathered from smartphone accelerometers from users who opted into the program. Moro and his collaborators took these data and, using specifically designed algorithms, determined when people walked, for how long, and for what purpose. They compared this information from before the pandemic, at different points throughout lockdown, and at a point when most restrictions had been eased. They matched the GPS-identified locations of the smartphones with census data to understand income level and other demographics.

      To make sure their dataset was robust, they only used information from areas that could reasonably be considered pedestrian. The researchers also acknowledge that the dataset may be incomplete, considering people may have occasionally walked without their phones on them.

      Leisure versus utilitarian walks were separated according to distance and/or destination. Utilitarian walks are usually shorter and involve stops at destinations other than the starting point. Leisure walks are longer and usually happen closer to home or in dedicated outdoor spaces.

      For example, many of the walks recorded pre-Covid-19 were short and occurred at around 7 a.m. and between 3 and 5 p.m., which would indicate a walking commute. These bouts of walking were replaced on weekends by short walks around noon.

      The key takeaway is that most walking in cities occurs with the goal of getting to a place. If people don’t have the opportunity to walk to places they need to go, they will reduce their walking activity overall. But when provided opportunity and access, people can supplement utilitarian activity with leisure walking.

      What can be done about it

      Taking into account the public health implications of physical inactivity, the authors argue a reduction in access to walking should be considered a second pandemic and be addressed with the same rigor as the Covid-19 pandemic.

      They suggest several tactical urbanization strategies (defined as non-permanent but easily accessible measures) to increase safety and appeal for both utilitarian and recreational walkers. Many of these have already been implemented in various cities around the world to ease economic and other hardships of the pandemic. Sections of city streets have been closed off to cars on weekends or other non-busy times to allow for pedestrian walking areas. Restaurants have been given curb space to allow for outdoor dining.

      “But most of these pop-up pedestrian areas happen in downtown, where people are high-income and have easier access to more walking opportunities,” notes Moro.

      The same attention needs to be paid to lower-income areas, the researchers argue. This study’s data showed that people explored their own neighborhoods in a recreational way more during lockdown than pre-pandemic. Such wanderings, the researcher say, should be encouraged by making any large, multi-lane intersections safer to cross for the elderly, sick, or those with young children. And local parks, usually seen as places for running laps, should be made more attractive destinations by adding amenities like water fountains, shaded pavilions, and hygiene and sanitation spaces.

      This study was unique in that its data came straight from mobile devices, rather than being self-reported in surveys. This more reliable method of tracking made this study more data-driven than other, similar efforts. And the geotagged data allowed the researchers to dig into socioeconomic trends associated with the findings.

      This is the team’s first analysis of physical activity during and just after lockdown. They hope to use lessons learned from this and planned follow-ups to encourage more permanent adoption of pedestrian-friendly pandemic-era changes.

      The Connection Science Group, co-led by faculty member Alex “Sandy” Pentland — who, along with Moro was a co-author on the paper along with six others from the UK, Brazil, and Australia — is part of the MIT Sociotechnical Systems Research Center within the MIT Institute for Data, Systems, and Society. The collaborative research exemplified in this study is core to the mission of the SSRC; in pairing computer science with public health, the group not only observes trends but also contextualizes data and use them to make improvements for everyone.

      “SSRC merges both the social and technological components of the research,” says Moro. “We’re not only building an analysis, but going beyond that to propose new policies and interventions to change what we are seeing for the better.” More