Pair of studies features biomechanical analysis of footwear
May 29,2008 – People who favor flip-flops as their primary footwear option during warm summer months may experience lower leg pain and a change in their stride, according to research presented today at the 55th Annual Meeting of the American College of Sports Medicine(ACSM) in Indianapolis.
“Flip-flops are very common, and this study began with the observation that most people appear to be wearing them beyond their structural limit,” said Justin F. Shroyer, lead author on the study. “It’s also apparent that individuals alter their gait while wearing flip-flops. Based on this, we expected to find that flip-flops may be a cause of pain in the leg or foot, and if so, would be counterproductive to alleviating that pain.”
The study compared flip-flops to sneakers to assess the angles at which they impact the floor and the force at contact with the ground during walking. Researchers analyzed the gait of flip-flop wearers compared to their gait while wearing sneakers.
By compiling the forces that the foot is exerting on the ground, they found a statistically significant decrease in the vertical (straight-down) force in flip-flop wearers. This decreased force may explain anecdotal evidence that persons who wear flip-flops alter their normal gait and therefore may shed light as to why some experience lower leg pain.
“Flip-flops are not designed for prolonged use or for walking long distances,” said Shroyer. “They lack the support that a walking or running shoe provides. Flip-flops should only be worn casually and for shorter periods of time. They probably should also not be a primary footwear choice.”
Shroyer also noted:
Some flip-flops on the market may provide more support, but are usually more expensive. For someone with lower-leg or foot problems, Shroyer recommends they limit their usage, and choose a flip-flop with more support.
Flip-flops should be replaced often. However, many people claim flip-flops are the most comfortable when they are “broken in,” just like a pair of sneakers. Flip-flops should be replaced every few months just as a runner would with running shoes.
Analysis of High-Heels
A new study supports the notion that women should use caution when descending stairs in heels, this time from a biomechanical perspective. An analysis of the motion at the ankle joint shows that walking in high heels down stairs may cause an unstable gait pattern that could lead to an injury of the leg or foot.
The study examined barefoot to low (one inch) and high (two-and-a-half inch) heels with several views of the foot and the heel to determine what patterns of motion predict how the lower leg and foot activate at these different heel heights.
While the heel strike force was the softest in the high heels, the force on the toe was highest in this shoe. Greater toe-off force is required to propel the body forward, and potentially contributes to the instability that may result in injury, particularly after long-term wear.
Researchers also found that when barefoot, participants had the highest heel strike. They also noted that when walking barefoot, participants landed with greater force at the heel strike, which may indicate a more confident approach to the last step.
“Walking barefoot has its advantages, such as giving the intrinsic muscles of the foot more work and therefore making them stronger,” said Wendy Miletello, Ph.D., who was involved in the study. “Stronger feet mean more stability for the entire body.”
“High heels are very common, at work or in our culture of fashion, and of course going up and down stairs is something we commonly do, even unconsciously at times,” said Lalitha Balasubramanian, lead author of the study. “This initial look at what happens when you wear heels on the stairs will help us determine what may predispose an individual to foot injuries, a common effect of wearing high heels for a long period. Future studies may look even more closely at injuries and fatigue related to wearing heels.”