“We found that when people walk in flip-flops, they alter their gait, which can result in problems and pain from the foot up into the hips and lower back,” Shroyer said. “Variations like this at the foot can result in changes up the kinetic chain, which in this case can extend upward in the wearer’s body.”
The researchers, in the AU College of Education’s Department of Kinesiology, recruited 39 college-age men and women for the study. Participants, wearing thong-style flip-flops and then traditional athletic shoes, walked a platform that measured vertical force as the walkers’ feet hit the ground. In addition, a video camcorder measured stride length and limb angles.
Shroyer’s team, under the direction of Dr. Wendi Weimar, associate professor of biomechanics and director of the department’s Biomechanics Laboratory, found that flip-flop wearers took shorter steps and that their heels hit the ground with less vertical force than when the same walkers wore athletic shoes. When wearing flip-flops, the study participants did not bring their toes up as much during the leg’s swing phase, resulting in a larger ankle angle and shorter stride length, possibly because they tended to grip the flip-flops with their toes.
Shroyer, who owns two pairs of flip-flops himself, said the research does not suggest that people should never wear flip-flops. They can be worn to provide short-term benefits such as helping beach-goers avoid sandy shoes or giving athletes post-game relief from their athletic shoes, but are not designed to properly support the foot and ankle during all-day wear, and, like athletics shoes, should be replaced every three to four months.
“Flip-flops are a mainstay for students on college campuses but they’re just not designed for that kind of use,” he said.
The study included thong-style flip-flops from well-known retailers and manufacturers and ranged in price from $5 to $50. Athletic shoes included in the study also ranged in price and style.
Shroyer’s interest in flip-flops has other footwear applications, as well as applications in other areas of biomechanics research. He will apply conclusions from the flip-flop study to his dissertation research on specialty athletics shoes and how they support the foot and aid in biomechanic performance.