Why Extra Cushioning in Your Shoes Might Actually Increase Stress on Your Feet

If you don’t own a pair of so-called high-stack or max-cushion running shoes yourself, no doubt you’ve seen others wearing them, whether at the gym, on trails or just knocking about town. Sandwiched between the tire tread-like outer sole and nylon upper is as much as 2 inches of soft and springy foam, which gives these shoes both the look and feel of walking around with mini-mattresses on your feet.

It all started back in 2010 with the introduction of the Hoka line of max-cushion shoes, which led other brands to develop similar styles, each stacked with its own patented lightweight foam. Now it is difficult to find running or walking shoes that aren’t raised on a platform of puff, some with the added oomph of a layer, or plate, of carbon fiber.

While max-cushion shoes may feel super comfy, and can improve running efficiency and performance if embedded with a carbon plate, there are concerns among podiatrists, orthopedists, kinesiologists and sports-medicine doctors about the long-term effects, not only on your feet, but also your ankles, knees and hips.

“They change people’s biomechanics in a way that can be unpredictable, and brings up the question of potential injury risk,” says Dr. Adam Tenforde, director of running medicine at Mass General Brigham’s National Running Center.

The problem comes down to basic biomechanics, says Dr. Kenrick Dennis, a podiatrist in Houston who served as medical director for the Houston Marathon.

“If you are standing on that marshmallow, it allows your foot to torque in and out a little bit more, the leg rotates to follow it, and that rotation is translated through the ankle, the knee and the hip,” he says.

It takes a bit longer to sink into the cushiness and subconsciously find your balance before you push off again, similar to the extra effort required when walking on sand. The wobbliness, he says, plus the added height of max-cushion shoes, also increases the risk of twisting an ankle or falling.

Moreover, max-cushion shoes diminish proprioception (awareness of where you are in space), since you have less sensory feedback of where you are vis-à-vis the ground.

A number of civil lawsuits have been filed against shoe manufacturers by track stars, including an Olympian, who allege, among other things, that wearing high-stack shoes with carbon plates caused injuries that derailed their careers. Nike faces one such suit in California Northern District Court. Puma—the parent company as well as some of its divisions and partners—was named in three cases filed in Massachusetts Superior Court.

Nike declined to comment on pending litigation, but in court filings the company denies its product is “defective and unsafe for its intended purposes” and neither “caused injury and/or contributed to the risk of injury.” Puma said in a statement that it strongly denies its shoes cause injury. The company is further pursuing a countersuit against its three accusers in a German court.

While the suits focused on shoes that included a carbon plate, Tenforde says max-cushion shoes can modify biomechanics independent of that feature. Hoka didn’t respond to requests for comment about safety concerns.

Of course, back when barefoot running was the rage in the mid-2000s, alleged injuries caused by zero-stack, or “barely there,” shoes resulted in lawsuits against manufacturers.

“The pendulum has swung from the barefoot shoes to now having a marshmallow under your foot,” says Dennis, the Houston podiatrist.

Proponents of max-cushion shoes, particularly those with an embedded carbon plate, point to studies that suggest the shoes improve running economy and performance by 4% and 2%, respectively. A 2023 review published in Sports Biomechanics says that every world record from the marathon to 5 kilometers has been broken by athletes wearing these kinds of shoes. The comfort and springy design may allow athletes to tolerate higher training volumes or intensities.

“If a shoe makes running easier, you will run faster,” says Dr. Laurent Malisoux, a sport and physical-activity research leader at Luxembourg Institute of Health. “But people should remember that if they get an injury, it’s because they probably ran too much, too fast or too soon, not because of the shoe.”

Nevertheless, concerns remain. A 2018 study published in Nature indicates max-cushion shoes actually increase the total load on muscles, bones and joints compared with more-moderately cushioned shoes in part because the foot is on the ground longer.

“You’re hitting the ground with the same magnitude of force,” says Dr. Daniel Lieberman, a Harvard evolutionary biologist whose research focuses on how modern footwear has altered human biomechanics. “But you’re spreading that force over a longer period of time.”

Your leg also appears to stiffen more when you land, intensifying the jolt, according to the authors of the Nature study. If there is a carbon plate in the shoe, it can help you spring back into the air a bit faster, but Lieberman says more research is needed to determine whether the total load is larger than in more moderately cushioned or minimalist shoes.

While max-cushion shoes may feel great initially, repetition of these minute wobbly, twisting moments plus the extra mechanical load on muscles, tendons, joints and bones could lead to injury in the long term, critics say. During a mile run, each foot will strike the ground on average about a thousand times. Running 20 miles a week adds up to a million foot strikes a year.

There is also the concern that the squishiness of max-cushion shoes and/or the location of the flex point, particularly if there is a carbon-fiber layer, may also shift where on your foot you land and push off. That might make you more vulnerable to foot fractures, according to a 2023 analysis of high-stack running shoes with carbon-fiber plates published in Sports Medicine, with Tenforde as the lead author.

Scott Christensen, lead endurance instructor for USA Track & Field, says while he appreciates the potential performance-enhancing qualities of bouncy foam and carbon springboards, “everything has a cost-benefit ratio to it.” One of the more counterintuitive costs, he says, is the shoes’ exceptional comfort. Runners don’t get as sore, which is the body’s way of saying: Hey! Back off before you do damage.

“As a coach, I want soreness,” Christensen says. “I depend on soreness in my athletes. Soreness is the governor of training.”

So, what is a person to do when confronted with a wall of shoes in a run shop or sporting-goods store? “The answer is there is no one answer,” Christensen says. People have different physiologies, exercise regimes and injury histories which might dictate not only level of cushioning, but also support, stability and heel-to-toe drop of the shoe.

Whether you’re a runner, walker or maybe someone whose job requires you to be on your feet all day, the best shoe is the shoe that fits. You may think you’re wearing the right size, but a 2018 study in the Journal of Foot and Ankle Research suggests as many as 72% of people wear shoes that don’t accommodate either the width or length of their feet. Your shoes shouldn’t hurt or feel uncomfortable either during or after physical activity.

And don’t pay attention only to the pillowy feel under your feet, Dennis says. Test your ability to maintain balance and coordination in the shoes by doing things like raising up on your toes and holding and then rocking back on your heels and holding, as well as doing quick turns and pivots. Notice any additional workload or twisting moments demanded of the joints and muscles in your legs and hips. Also listen to your footfall. It should be light and have a steady, crisp cadence—no clomping, scuffing or shuffling, as can happen when you have too much bulk under your feet.

Beyond that, Christensen’s advises training in more than one kind of shoe, varying amount of cushioning and stack height. The combination will vary stressors on your body and reduce the chance of repetitive foot strike and motion injuries.

Dr. Stéphane Bermon, director of the health and science department at World Athletics—the international governing body for track and field, cross-country running, road running, race walking, mountain running and ultra running—is also a proponent of the shoe-rotation strategy, but he cautions to introduce any new shoe “very, very progressively” to avoid injury. Maybe running or walking in a new kind of shoe once a week for one week and then twice a week the following week, and so on.

“In biomechanics, in human physiology, what kills you is routine,” Bermon says. “Whether it’s your bone, whether it’s your muscle, whether it’s your tendon, you have to challenge yourself every day with different things.” In shoes, just as in life, “There is nothing worse than monotony.”

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