The toe of most shoes, notably sneakers, bends ever so marginally upward. While this curve, called a toe spring, can make stepping more comfortable and easier, it may also weaken feet and open them up to some common (and debilitating ) foot-related issues.
That’s the conclusion reached by Harvard evolutionary biologist Daniel E. Lieberman, his former undergraduate student Oliver B. Hansen ’19, and two former post-doctoral researchers, Freddy Sichting and Nicholas B. Holowka, who studied toe springs and their effect on the biomechanics of walking. Their research is detailed in a brand new variant of Scientific Reports.
The more curved a toe spring is, the less power the foot inside the shoe has to use when pushing off from the ground while walking. Meaning foot muscles do less work, and this, the researchers hypothesize, may have consequences.
The researchers say this potential weakness could make people more susceptible to medical conditions like plantar fasciitis — a common, difficult to repair, and painful inflammation of the thick, web-like band of tissue that connects the heal to the toes.
“One of the biggest problems in the world today of people’s feet is plantar fasciitis,” Lieberman said. “We think that what happens is that people are relying on their plantar fascia to do what muscles normally do. When you get weak muscles and the plantar fascia has to do more work, it’s not really evolved for that, and so it gets inflamed.”
The scientists say their next step is to confirm their hypothesis in future research.
“From an evolutionary perspective, wearing modern shoes that have arch supports, cushioning, and other supportive features is a very recent phenomenon,” said Sichting, who’s now a professor of human locomotion at Chemnitz University of Technology in Germany and served as the paper’s first author. “Several lines of evidence suggest that weak foot muscles may be partly a consequence of such features. In our research, we were interested in a nearly ubiquitous element of modern shoes that has not been studied before: the upward curvature at the front of the shoe.”
He means that the toe spring, of course, which always flexes the toe box above ground, and it has become almost ubiquitous in contemporary footwear, especially in athletic sneakers.
The project began after Sichting and Lieberman met at a conference In Boston, also (obviously ) went for a run by the Charles River in which they talked about foot biomechanics and plantar fasciitis. Hansen worked on the paper as part of the senior honor’s thesis.
It became apparent while analyzing the data that the propulsive force Generated from the metatarsophalangeal or MTP joints (that’s where the toes connect to the rest of your foot bones) decreases as the curve of the toe spring on the specially-made vases increased. MTP joints are among the crucial characteristics that have evolved so that humans can walk and run on two feet so effectively and efficiently.
“By reducing moments at the MTP joints, toe springs likely relieve the intrinsic foot muscles of some of the work necessary to stiffen these joints,” the researchers wrote in the study. “These small differences in muscle work likely add up to substantial differences over time when considering that the average individual in industrialized countries takes 4,000 to 6,000 steps per day. Thus, habitually wearing shoes with toe springs could inhibit or de-condition the force generating capacity of intrinsic foot muscles.”
The researchers make clear that more study is needed on all fronts and that their study doesn’t directly link toe springs together with plantar fasciitis or other common foot issues. The analysis also contained only habitual shoe consumers whose feet might already have been adapted to shoes with toe springs.
“This study isolated just one element of our shoes,” said Hansen. “More research is needed to investigate how toe springs interact with other elements of shoes such as stiff soles or cushioning. This could give us a more complete picture of how shoes affect our biomechanics.”
However, they say the unrecognized biomechanical effects of toe springs on foot functioning merits additional consideration.
“Walking in shoes with comfortable features such as a toe spring has its costs,” Sichting said.
Don’t anticipate toe springs to go anywhere anytime soon, however.
“We like comfort,” Lieberman said. “That’s why we sit in chairs and take elevators.”
Related Journal Article: https://www.nature.com/articles/s41598-020-71247-9