The Nike Vaporfly 4% wasn鈥檛 shy about how much of a boost it claimed to give runners: the promise was right there in the name. When the shoe was released back in 2017, researchers at the University of Colorado published data showing that it improved athletes鈥� running economy (i.e., efficiency) by an average of 4 percent over the best marathon shoes at the time. Chaos鈥攁nd a whole bunch of world records鈥攅nsued.

The key ingredients in the Vaporfly were a stiff, curved carbon-fiber plate embedded in a thick layer of soft-but-resilient midsole foam. Neither of these elements was magical on their own, but they somehow combined to make runners substantially more efficient, for reasons that scientists don鈥檛 fully understand and are still arguing about. Since then, virtually every major shoe brand has come up with multiple iterations of the so-called 鈥渟upershoe,鈥� tweaking these basic ingredients in minor and sometimes major ways.

But a key question has remained mostly unanswered: are the newest shoes significantly better than the original Vaporfly? A few researchers have run head-to-head tests of models from different brands, with generally muddled results. Some newer shoes might be a percent or two better, but there鈥檚 so much individual variation that it鈥檚 hard to be sure. Since Nike鈥檚 bold move in 2017, the shoe brands themselves have mostly steered clear of making explicit claims about how good their shoes are.

That鈥檚 about to change. Puma, a veteran shoe brand that relaunched its serious running line in 2018, has a new shoe dropping in time for this month鈥檚 Boston and London marathons. They think it鈥檚 dramatically better than anything else on the market鈥攁bout 3.5 percent better, in fact. They鈥檙e so convinced that they arranged to have the shoe tested by Wouter Hoogkamer, the head of the Integrative Locomotion Laboratory at UMass Amherst and, as it happens, the man who led the external testing of Nike鈥檚 Vaporfly back in 2017. Hoogkamer released his data earlier this week, and it鈥檚 impressive.

What the New Data Shows

Hoogkamer鈥檚 study is posted as a preprint on bioRxiv, a site where scientists share their results while awaiting peer review. He and his colleagues brought in 15 volunteers, all of whom had run under 21 minutes for 5K (for women) or 19 minutes (for men). To test their running economy, he had them run on a treadmill for five minutes at a time while measuring their oxygen consumption. The more oxygen you consume at a given pace, the more energy you鈥檙e burning and therefore the less efficient your movements. A good shoe should maximize your efficiency鈥攁nd therefore minimize your oxygen needs鈥攁t a given pace.

Each runner had their economy tested eight times: twice each in four different shoes. The comparison shoes were the Nike Alphafly 3 (which Kelvin Kiptum used to set the men鈥檚 marathon world record and Ruth Chepngetich used to set the women鈥檚 record); the Adidas Adios Pro Evo 1 (which Tigst Assefa used to set the previous women鈥檚 marathon world record in 2023); and Puma鈥檚 top-of-the-line . The newest Puma supershoe is an update of this latter model. It鈥檚 been dubbed the Fast-R Nitro Elite 3 (original, I know).

Without further ado, here鈥檚 the running economy data for the four shoes. Metabolic rate, in watts per kilogram, tells us how much energy the runners were burning at a prescribed pace that was assigned based on their 5K PR, ranging between 6:00 and 7:30 per mile. The thick line shows the average results, the thin lines show the individual ones.

It鈥檚 clear that the Fast-R3 resulted in the lowest metabolic rate across the board鈥攚hich means it鈥檚 the most efficient shoe. The runners burned 3.6 percent less energy wearing the Fast-R3 than they did in the Nike shoe, and 3.5 percent less than in the Adidas. (Some free marketing advice: they should have called the new shoe the Fast-R3.5.) It also burned 3.2 percent less energy than the Fast-R2鈥攎aking the new model pretty significant update from its own previous edition. What鈥檚 even more remarkable, given the wide range of individual results seen in previous supershoe studies, is that every single one of the 15 runners was most efficient in the Fast-R3.

Puma has also run its own internal testing on more than 50 runners, according to Laura Healey, who heads the brand鈥檚 footwear innovation team. In their data, the shoe is 3.3 to 3.5 percent better than its rivals. Running economy doesn鈥檛 translate directly to race time, but a boost of 3.2 percent (the margin between the Fast-R2 and the Fast-R3) is expected to reduce race times by about 2.0 percent for a 2:00 marathoner, 2.6 percent for a 3:00 marathoner, and 3.3 percent for a 4:00 marathoner.

What鈥檚 the Magic Ingredient?

With the Vaporfly, it was easy to understand鈥攁t least superficially鈥攚hy the shoe was different from its peers at the time: it had that thick foam and carbon plate. It鈥檚 harder to get a handle on what makes the Fast-R3 special, because the basic architecture is the same. The differences between the Fast-R2 and Fast-R3 are subtle, but the running economy data shows that they鈥檙e significant.

Puma鈥檚 team started with the Fast-R2 and created a virtual model of the shoe using biomechanical data collected from ten runners wearing pressure-sensing insoles while running on a force-sensing treadmill. The model showed exactly what was happening inside the shoe at each instant during a running stride: where the forces and strains were highest and lowest, how the shoe was bending and compressing, and so on.

Then they went through a process of iterative computational design and optimization. For example, if the virtual model showed that a particular area in the midsole wasn鈥檛 experiencing much strain, they would remove some of the foam in that location. Or if it showed that a region of the carbon plate was excessively strained, they would reinforce it with a rib of extra carbon. All this was done digitally within the virtual model, so they could see if the changes made the situation better or worse without going through the hassle and expense of building a new prototype.

By the time they finished this virtual optimization process, they鈥檇 snipped away enough superfluous foam and carbon to reduce the weight of the shoe by more than 30 percent, from 249 grams to 167 grams. There鈥檚 a rule of thumb that adding 100 grams to a shoe worsens running economy by about 1 percent, so this 82-gram reduction accounts for about 0.8 percent of the Fast-R3鈥檚 advantage. As for the rest, there鈥檚 no single obvious change that explains it. Instead, the iterative process of making sure every bit of foam and carbon fiber is contributing seems to have created a more efficient shoe.

There are some other subtle differences. The Fast-R3 is a little less stiff than its competitors when you try to bend it along its length, and a little less stiff when you compress the midsole鈥攂ut it returns slightly more energy when it springs back. The foam in traditional running shoes returns about 65 to 75 percent of the energy you spend compressing it. Superfoams such as PEBA in the Vaporfly and other supershoes return about 85 percent. Puma鈥檚 Nitro Elite foam, an 鈥渁liphatic thermoplastic polyurethane鈥� (A-TPU), returns over 90 percent. In Hoogkamer鈥檚 testing, compressing the whole shoe (not just the midsole foam) returned 89.9 percent of the energy, compared to 85.0 percent in the Nike shoe and 85.7 percent in the Adidas.

What Happens Next?

There are a lot of reasons to be skeptical of any shoe company鈥檚 claims about its newest model. Hoogkamer doesn鈥檛 work for Puma, but his study was funded by them, just as his Vaporfly study was funded by Nike. Both studies were small. Subsequent events showed that the Vaporfly鈥檚 4-percent boost was real and spectacular. Over the coming weeks, we鈥檒l get a sense of whether the Fast-R3鈥檚 3.5-percent boost also passes the real-world test.

One problem is that Puma鈥檚 roster of elite road runners isn鈥檛 as impressive as Nike鈥檚 or Adidas鈥檚. At first glance, they don鈥檛 have anyone who鈥檚 likely to set an attention-grabbing world record. Still, we鈥檒l start seeing the new shoe in action at the Boston Marathon on April 21 and the London Marathon on April 27.

One of the athletes who will be wearing it in Boston is Rory Linkletter, a 2:08 marathoner from Canada. He鈥檚 been training in the shoe, so I asked whether he could tell that it was different. He said the first thing you notice is how light it is, and the second is the springiness: 鈥淚t鈥檚 softer than previous supershoes, and that softness is met with some pretty remarkable bounce.鈥� He doesn鈥檛 have enough experience with it to know whether it鈥檚 faster, but he鈥檇 just done an 8-mile tempo run along Lake Mary Road in Flagstaff that was a minute faster than he鈥檇 ever previously done.

If Linkletter sets a big PR in Boston, it will be impossible to know how much credit, if any, should go to the shoe. But over the months to come, we might start seeing some patterns鈥攁nd seeing whether other shoe companies adopt similar computational approaches, if they haven鈥檛 already. The 鈥渕any small tweaks鈥� approach of the Fast-R3 means there鈥檚 no single gimmick to copy. It also means that further refinements might be possible. Five years ago, I wondered whether supershoes were like klapskates in speedskating (one big innovation followed by a plateau) or tech suits in swimming (a series of innovations that kept making swimmers faster and faster). It鈥檚 starting to look like option B.

鈥�

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You know the shoes Ruth Chepngetich and Eilud Kipchoge wear, partially responsible for some of the fastest marathon times ever recorded? Those are called super shoes. They鈥檙e thick-soled, with ultralight, hyper-responsive foam midsoles embedded with carbon-fiber plates. Think of super trainers as the more easygoing but still light and responsive cousins of super shoes. We sliced one open at our gear lab in Colorado to find out what makes them go zoom.

Midsole Foam

At the heart of every super shoe and super trainer is a thick slab of high-tech foam that鈥檚 lighter, softer, and bouncier than any other midsole material to date. It鈥檚 created by a process called supercritical foaming that combines heat, pressure, and liquid gas to infuse bubbles into elastic polymers like PEBA, TPEE, and ATPU. The resulting midsoles deliver plush cushioning and trampoline-like 颅rebound, but are squishy and unstable, requiring a balanced, 颅powerful stride to optimize performance.

Super shoes have full stacks of these soft, bouncy foams. However, many super trainers, like the shown here, use a combination of foams鈥攕ofter on top of firmer鈥攖o provide an energetic feel while delivering the kind of stride-supporting ride more suitable for a training shoe. The step-in feels soft underfoot, but when put through a heel-compression
test used to at the 国产吃瓜黑料 Lab, the Deviate Nitro 3 super trainer was less squishy than all the racers we tested.

Traditional trainers use foams that are firmer and more supportive or are soft but not as bouncy鈥攗sually EVA or an EVA blend鈥攄elivering a more grounded, rolling ride.

Plate

All super shoes have a rigid, curved carbon-fiber plate embedded in the midsole. While many assume that this acts like a spring, research has shown that its role is to moderate the foam鈥檚 squish and channel its rebound, reducing energy loss and facilitating powerful push-offs.

Super trainers also typically have an embedded plate, but one with more flex. While rigid plates provide the most pop, they also dictate how the shoe rolls forward and can negatively alter the stride. A super trainer鈥檚 plate鈥攍ike the one in the Deviate Nitro 3, made of a carbon-composite weave with a forked forefoot shape鈥斅璦ccommodates a wider range of paces and strides and is less prone to bouncing feet in unproductive directions when form deteriorates from fatigue.

Plates differ in flex, shape, and location within the foam. This 颅affects how the foot rolls and interacts with the ground, and each feels different when combined with a runner鈥檚 unique stride.

Rocker

With the thick foam in many of today鈥檚 running shoes, the sole no longer flexes much at the ball of the foot. Instead, the foam鈥檚 height allows designers to cut away mass under the toe, creating a rocker shape. Rather than enabling the foot to flex as it moves through the stride, that shape allows the runner to roll off the toe while the foot remains in a neutral position. The rocker鈥檚 starting point, slope, and relationship to the plate all affect the shoe鈥檚 ride. In our measurements, the Deviate Nitro 3鈥檚 rocker started 8 percent later (closer to the toe) than the rocker on Puma鈥檚 Fast-R Nitro 2 racing super shoe, providing a stabler forefoot stance before rolling forward.

Outsole

A three-millimeter-thick rubber outsole covers more than 90 percent of the forefoot and all contact areas of the heel on the 颅Deviate Nitro 3. This provides better grip and durability than the sole of a racer, which needs to be as light as possible and so has rubber only in small, optimized zones.

Upper

Super-shoe racers have minimal uppers with scant padding and strong, secure grip to hold the foot in place at speed. A super trainer鈥檚 upper is more plush and durable but still lightweight, thanks to strategically placed fabrics that stretch, breathe, or 颅support as needed.

Featured Super Trainer

Puma Deviate Nitro 3听

Weight: 10.1 oz (men鈥檚)
Stack Height: 39 mm (heel); 29 mm (forefoot)
Drop: 10 mm

听

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Everyone has a plan, Mike Tyson famously said, until they get punched in the face. The endurance athlete鈥檚 version of that dictum might be: everyone has a great VO2 max and an efficient running stride until they鈥檝e run 20 miles. How you fare in those final miles depends, in large part, on how steeply these factors have declined over the course of the race.

This is the fundamental premise of 鈥渇atigue resistance,鈥� an idea I first wrote about back in 2021 that is currently one of the hottest topics in endurance science. The old view was that you could run some lab tests to determine an athlete鈥檚 VO2 max, lactate threshold, and running economy (or an equivalent measure of efficiency for other sports) and calculate their predicted finishing time. The new insight is that these factors change as you fatigue鈥攁nd crucially, they change more in some people than others. Having good fatigue resistance, then, is the 鈥�fourth dimension鈥� of endurance.

So far, most of the research on fatigue resistance鈥攚hich is also called 鈥渄urability鈥� or 鈥減hysiological resilience鈥濃�攈as focused on demonstrating that it plays a role in determining who wins races. What we really want to know, of course, is how to improve it. That鈥檚 the question a pair of new papers tackles.

The Case for Strength Training

The first study, by Michele Zanini and his colleagues at Loughborough University in Britain, tests a twice-a-week strength training program in 28 well-trained runners with an average 10K best of 39 minutes. Half of them added the strength routine to their usual training for ten weeks, while the other half just carried on with their usual training.

The performance test was a 90-minute run at a pace near lactate threshold, followed by an all-out time-to-exhaustion test that lasted about five minutes. Every 15 minutes during the 90-minute run, they measured running economy, which quantifies how much energy you burn to sustain a given pace. They expected running economy to get worse as the runners fatigued, but wanted to find out whether strength training could counteract this deterioration.

The results were encouraging. Before strength training, running economy got 4.7 percent worse after 90 minutes of running; after strength training, it only declined by 2.1 percent over the same period of time. Here鈥檚 how running economy changed over the course of the run, with white circles showing the baseline test and black circles showing the post-strength-training test:

Note that a positive change (i.e. the line drifting upward) means that the runners were burning more energy to maintain the same pace as time went on. In the baseline test, running economy starts getting significantly worse after about an hour. After strength training, this drift is less pronounced.

The strength training program in the study consisted of a mix of heavy weights and explosive plyometrics. The resistance exercises were the back squat, single-leg press, and seated isometric calf raises, typically with around three sets of six reps. The plyometrics included vertical exercises (pogo jumps and drop jumps) and horizontal exercises (hops and bounding). It鈥檚 not clear from this study whether the heavy weights or the plyometrics provided the magic, though Zanini that both methods have produced similar results in previous studies of strength training and running economy.

Why does strength training improve fatigue resistance? Here we鈥檙e limited to speculation. It may have something to do with making fast-twitch muscle fibers more efficient, or making tendons stiffer and springer, or improving strength sufficiently to maintain good running form for longer.

Other Options for Boosting Fatigue Resistance

The other new paper is by Andy Jones of the University of Exeter in Britain and Brett Kirby of the Nike Sport Research Lab. Jones and Kirby played key roles in Nike鈥檚 Breaking2 Project in 2017, where they encountered what you might call the Zersenay Tadese Problem. Tadese had exceptional lab values, including the best running economy ever measured, but repeatedly struggled at the marathon distance, while his teammate Eliud Kipchoge had relatively modest lab values but turned out to be the dominant marathon runner of the decade. The difference, presumably, was that Kipchoge had better fatigue resistance.

The new paper sums up their thoughts on fatigue resistance, including some speculation on how to improve it. Strength training, they note, is one option鈥攖hough they point out that few of the East African runners who currently dominate international marathoning do structured strength training.

Overall, their view seems to be that the best ways of improving fatigue resistance are mostly the things that endurance athletes already do to get better: high mileage, especially accumulated over many years; long runs, including some sections at close to race pace; intense interval sessions; following a pyramidal training distribution. There may also be some more subtle effects from, for example, doing some fasted training or living at high altitude. None of these are uniquely targeted at fatigue resistance.

Jones and Kirby do mention one other possibility: put on some supershoes. There鈥檚 likely an instant effect, since the heavy cushioning reduces muscle damage and enables you to keep striding smoothly through the later stages of a marathon. And there may also be a chronic effect: the cushioning allows you to absorb and recover from higher levels of training, enabling you to safely rack up higher mileage and thus improving your fatigue resistance over time.

The overall impression, then, is more evolution than revolution. All these years, we鈥檝e been training to maximize VO2 max, running economy, and threshold. Now we鈥檝e got a new target鈥攆atigue resistance鈥攂ut so far the best ways of improving seem to be mostly the things we鈥檙e already doing. Even Zanini鈥檚 strength-training routine is the kind of thing coaches and scientists already recommend. But if you have the sense that fatigue resistance is one of your weaknesses, you now have extra motivation to move strength training and plyometrics from the 鈥淚 should do this鈥� column to 鈥淚鈥檓 doing it.鈥�

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