Are minimalist shoes the right choice for all of your runs? While the movement toward whisper-weight trainers—or no shoes at all—began more than a decade ago and has faded as of late, the question of whether the footwear can help or hurt performance is still hotly debated.
Here’s something else to add to the discussion: In a new study published in the Does a Shoes Heel-to-Toe Drop Matter, researchers found that when runners gradually incorporated minimalist shoes into their training, their calves and certain stabilizing muscles in the foot grew stronger—but only up to about 35 percent of weekly mileage in the shoes.
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Led by Australia’s Macquarie University physiotherapy and biomechanics expert Joel Fuller, Ph.D., the six-week study followed 50 male runners between the ages of 19 and 35 who ran somewhere between 7.5 and 25 miles per week. To be eligible for the study, the men had to be injury-free, use conventional running shoes, exhibit a heel-strike running form, and be recreationally competitive (in this case, able to run a 5K in less than 23 minutes).
For the first six weeks of the study, the runners were provided a training program and randomly divided into two groups—in one, runners wore conventional shoes (The Fli-Lyte Proves Its Okay to Be a Lightweight) 35 percent of the time. In the other group, participants ran in minimalist shoes (Asics Piranha SP4).
When the participants took a 5K time trial on a treadmill at the end of this part of the study, the minimalist group finished slightly faster on average and ran more efficiently, though the results were marginal. There was also no difference in the groups’ stride length or foot strike. (All of the runners continued to heel-strike after the study ended.)
The other notable finding of the study was that the runners who trained in the minimalist shoes—especially those who ran more than 22 miles a week—improved their plantar flexor strength more than those in conventional shoes. The complex network of muscles involved with plantar flexion—including the calves and ligaments wrapping around the arches and bottoms of feet—is seriously tapped into when runners sport barely-there footwear.
After the six-week training period ended, a 20-week follow-up study commenced, during which runners were asked to increase the use of their allocated shoe by 5 percent each week for 20 weeks while following their own training program—until they were training in nothing but their prescribed shoe.
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The gains in lower leg and foot strength, however, only increased to a point. The study found that runners benefited the most when wearing minimalist shoes 35 percent of the time; when worn any more than that, they didn’t get any faster or stronger. In fact, the researchers advised against training in minimalist shoes full-time, as there weren’t any extra benefits—but a lot more potential risks.
“Using them more than 35 percent of the time can raise injury risk, particularly if you have increased body mass,” Fuller wrote in an email to Runner’s World. Namely, the ankle and metatarsals come under extreme stress when using minimalist shoes on such a consistent basis.
The missing ingredient in their study, Fuller said, is that they didn’t monitor training for the 20-week follow-up, meaning training intensities could have fallen off for both groups. In the future, Fuller would also like to test the effects of minimalist shoes on female runners.
Regardless of the minimalist versus conventional debate, Fuller said, “Ensuring optimal training is the most important thing that you can be doing, so prioritize that over footwear.”
Bottom Line: If and when you decide to go minimal, be sure to work them into your shoe rotation slowly. They can be helpful for your training or racing, but this study (and others) show that getting in all of your miles with more minimal shoes has a certain ceiling for performance benefits.
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