Curve at Shoe Tips may Lead to Weaker Muscles

The curve at the tip of shoes, known as toe spring, makes movement comfortable and easier but weakens feet and opens to common and painful foot-related problems, revealed 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. Their research is detailed in a new edition of Scientific Reports. The potential weakness makes people more susceptible to medical conditions like plantar fasciitis, a common, hard to repair, and painful inflammation of the thick, web-like band of tissue that connects the heel bone to the toes.

"It stands to reason that if the foot muscles have to do less work, then they're probably going to have less endurance given that many thousands of times a day you push off on your toes," said Lieberman, the Edwin M. Lerner II Professor of Biological Science and senior author on the paper.

"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."

In the experiment, 13 participants walked barefoot on a specially designed treadmill with four custom-made sandals. The treadmill is equipped with force plates and an infrared camera system to measure how much power is put into each step. The sandals each had varying degrees of toe spring angles -- from 10 degrees to 40 degrees and are designed to mimic the stiffness and shape found in commercially available shoes.

The propulsive force generated by the metatarsophalangeal or MTP joints decreased as the curve of the toe spring on the specially-made sandals increased. MTP joints are one of the key features 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."

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The researchers make clear that more research is needed, that their study does not directly link toe springs with plantar fasciitis or other common foot problems.

Source-Medindia