These Legal Doping Strategies Are Reshaping Endurance Sports. Here's How They Can Make You Faster

Tom Evans, a UK-based ultrarunner, was on a flat stretch of trail near the halfway point of the 106-mile Ultra-Trail du Mont-Blanc (UTMB) course in Chamonix, France, when he realized he had a small lead on the rest of the pack. One minute to be exact. It wasn’t much and he knew it. 

“I thought to myself, I need to start fueling more now, rather than waiting till the time where I’m going to start working harder,” Evans says. 

So he took down a mix of high-carb drinks and gels and, an hour later, started up the Grand Col Ferret, a grueling ascent that gains 2,500 feet in under three miles. By the top of the climb, he’d stretched his lead to five minutes. Fifty miles later, he crossed the finish line 30 minutes ahead of the next competitor.

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Evans’ win at the 2025 UTMB was a textbook example of how endurance athletes are personalizing their fueling to perform at the highest level. Every decision, from how much Evans ate to when he ate it, had been tested and fine-tuned using data and lab work. All he had to do was execute his plan to maintain energy over the course’s most brutal stretches.

Across sports like long-distance running, cycling, and triathlon, athletes are using science-backed interventions to push the limits of what the human body can do. With each innovation comes faster races, broken course records and new fastest-known-times (FKTs). From high-carb fueling to cooling technology to heat training, these strategies all tap into the same basic physiological principle: improving the body’s ability to deliver oxygen and use it efficiently, says Brad Wilkins, Ph.D., exercise physiology and endurance performance researcher at the University of Oregon. And while they don’t offer the same performance benefits of illegal doping methods like blood transfusions, which have been shown to boost performance by up to seven percent, they don’t come with the major health risks and career-ending penalties either. These legal approaches may offer a two to three percent advantage, acting as a kind of “legal doping.” When the goal is to eke out even a tiny competitive edge, every small performance boost matters.

Which ones are worth adding to your routine? We talked to researchers, coaches, and athletes about the science behind these methods to find out.

The High-Carb Movement

For years, endurance athletes followed the fueling recommendation of 60 to 90 grams of carbs per hour—the maximum amount researchers believed the gut could absorb and muscles could oxidize during exercise. That number came from early studies that assumed digestion was a fixed process; going above that threshold would only result in stomach cramps (or worse). But newer research suggests that figure wasn’t static, and athletes began pushing limits. They realized the gut could be trained like a muscle, too.

“High-carb” fueling refers to taking in anything over the traditional range during training runs and races, says Kylee Van Horn, R.D.N., a sports dietitian specializing in endurance sports. Among all the modern performance hacks, this one is perhaps the best researched and the most immediately impactful for men and women.

David Roche, who set the course record two years in a row at the Leadville 100-mile trail race, hailed it as a “revolution” on his podcast “Some Work, All Play.” He predicts it’ll upend endurance sports and allow athletes to push progressively faster paces. 

In a 2025 study in the Journal of Applied Physiology, elite marathoners had a metabolic advantage when they took in 120 grams of carbs instead of 60, while a 2020 study showed that the same amount could limit muscle damage during a mountain marathon. Van Horn says that many of her clients on high-carb plans report sustained energy and faster recovery times.

The reasoning is simple: Glycogen, the body’s stored form of carbohydrate, is what keeps your muscles firing. When it runs out, so does your energy. By taking in more external carbs during exercise, you preserve your internal glycogen stores longer, “and the better off you’re going to be,” says Wilkins. It’s an area where athletes are now leading the science, experimenting far faster than research can validate, says Van Horn. 

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When Olympic marathon runner Rory Linkletter started his professional career six years ago, there wasn’t much guidance on fueling strategies. He’d grab bottles of sugary drink mix at aid stations but never tracked the numbers. These days, he aims for 100 grams of carbs an hour during both training runs and races. If he can take in more, he does. 

“At the beginning of my career, I’d get to an hour and a half in the race and I would have to hold on for dear life,” says Linkletter. “Since I’ve gotten better at fueling in the marathon, I undoubtedly have a better second half of the race than I ever did in my career. I still get tired—my legs start to hurt and the pace gets harder—but my body’s not completely shutting down like it did.” 

And Linkletter’s intake is relatively conservative. Some pros, like Roche, push past 120 or even 150 grams per hour—the equivalent of more than three cups of white rice. Joe Klecker, an On Running athlete, consumed 175 grams of carbs an hour to place 10th at his marathon debut in NYC this fall. Most of it comes in gel or drink form, because eating that much solid food mid-race is unthinkable (and far too heavy to carry). 

The challenge, of course, is digestion. Too many carbs too quickly can be a gastrointestinal nightmare. To get around that, brands are blending carb sources—maltose, dextrose, and fructose—that use multiple absorption pathways in the gut, rather than relying on one, like glucose, alone, says Wilkins. He recommends experimenting with products to find what works, while Van Horn says you should “train the gut” in small increments—adding about 10 grams per hour per week during your runs—to adapt to the heavier load before race day.

Still, as Evans learned during his 19-hour run at UTMB, there’s no universal formula. He knew his gut was sensitive to ultra-high carb counts so his team performed in-lab breath analyses, which showed that he burned a ton of carbs on uphills, but barely any on the descents. “We used a traffic light system: Green being high carb, amber being medium carb, red being low carb,” he says. As he ran the flats, he would fuel high—up to 110 grams per hour—to prepare for the ascents. On the climbs, he would pull back his intake to 80 grams before the descent. This variation helped him maintain energy while avoiding stomach issues.

But as social media gives casual runners access to pro-level intel, Jason Koop, ultra running coach at Carmichael Training Systems, says we should avoid playing monkey see, monkey do. Personalization is key. 

“If you’re just putting carbohydrates in your body for the sake of it, it’s not going to work,” Evans says. “Imagine you’ve just fueled up your car and you try to put more in—it’s just gonna overflow. And when you’re running, it’s got two places to come out. And neither are particularly pleasant.” 

Smarter Supplements

If there’s a supplement making a comeback, it’s sodium bicarbonate (often nicknamed bicarb)—the same chemistry as the baking soda in your pantry. It buffers the build up of lactic acids in your blood, helping the legs to feel fresh for longer, says Wilkins. Scientists have been researching its effects on athletic performance since the 1930s and it’s been shown to lead to significant gains for short, high-intensity efforts up to 12 minutes, according to a study in the International Society of Sports Nutrition. “I was an 800-meter runner in college—a 20 year old kid in 2002—and we used to mix up baking soda in a little glass and take it before runs,” says Koop. 

For decades, marathoners never touched it. The research was on short-duration sports like sprinting, rowing, and boxing, so the side effects like nausea and bloating weren’t worth the risk. 

But lately, even long-distance athletes are experimenting with it. Kilian Jornet, one of the most influential ultrarunners in the world, used it before his 2022 UTMB win. The science is still catching up, says Van Horn. Researchers are just beginning trials to measure the effects during prolonged exercise, but many athletes say it helps.

Part of sodium bicarbonate’s revival comes from smarter formulations. Brands like Maurten have developed a goopy mix that packages bicarb into a hydrogel to minimize the gut distress that once made it a risky pre-race choice. Other supplements are emerging on the same principle: Nomio, for instance, uses compounds derived from broccoli sprouts to lower lactic acid levels by up to 12 percent when you take it three hours before a race, the brand claims. “Everybody’s using it now,” says Linkletter.

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Superior Supershoes

At the top levels, the biggest changes in performance in the last few years have come from equipment more than anything else, says Koop. Namely, the super shoe revolution, which “led to a seismic leap in performance almost overnight,” he adds.

The data is pretty clear: For road runners, carbon-plated “supershoes” have been shown to improve running economy by three to four percent—a massive margin in elite racing. For amateurs, the advantage depends on pace and biomechanics, but many still see a boost.

Now, brands are pushing the concept even further. During Adidas’ Chasing 100 project—where five runners attempted to break the six-hour barrier for 100 kilometers—Marc Makowski, the company’s senior vice president of creative direction and innovation, and his team built personalized shoes for each athlete. They first measured each runner’s economy and biomechanics. “We looked at different foams, stack heights, and stiffening elements to identify what's the best configuration for each of the runners,” he says. The result: Sibusiso Kubheka crossed the finish line in 5 hours, 59 minutes, and 20 seconds, averaging a 5:47-mile pace. The shoes, with foam pressurized to precisely Kubheka’s liking and the outsole customized to the millimeter, would be illegal in most marathon events, but that wasn’t the point. “We wanted to see what was possible when there were no limits,” says Makowski.

Trail running hasn’t seen the same measurable leap—terrain and conditions make it hard to replicate results in a lab to really see any data to support it—but that doesn’t mean the innovation has stopped. Evans wore an Asics prototype of an upcoming model at UTMB, which he calls the “swiss army knife of trail running shoes”: Fast, nimble, and plated for easy sections, but without an aggressive rocker shape so it still feels stable on the rocky terrain that makes the Alps iconic. He says that it’s more about picking the right shoe for the race conditions, rather than expecting any one shoe to maximize your performance across the board.

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Playing With Fire

Another intervention nearly every expert agrees on is heat adaptation training. “When you adapt to heat stress, your blood volume expands, which makes you better at thermoregulating,” says Wilkins. You’ll end up sweating more and dumping heat more efficiently. “If you do nothing else before running a marathon, 10 to 14 days of heat training would be beneficial, no matter if it's going to be a hot day or a cold day,” he adds.

There are two ways to get the benefits. Active heat training means running in high temperatures while donning a space-style suit (or just a few extra layers). Passive heat training uses saunas and hot tub sessions to create the same adaptations with less stress on the body.

Wilkins recommends combining active and passive methods, while Koop says that the passive version is easier on the body and less likely to interfere with recovery. You’ll see the effects fairly quickly: “20 minutes a day, six days a week for two weeks—you get 98 percent of the way there,” says Koop. However, the benefits also fade fairly quickly.

Over time, continued heat adaptation may yield deeper gains, especially in already endurance-trained athletes. “Long-term exposure can increase hemoglobin mass,” says Wilkins, which means more oxygen-carrying capacity, essentially mimicking some of the effects of altitude training. This is likely too intensive for the average athlete, as multiplestudies have found that athletes needed to perform five 50-minute workouts a week for five weeks in a heat suit or similar gear to see results.

Either way, hydrate well. The goal is to sweat a lot, so you don’t want to stress your kidneys from dehydration. And Wilkins says that while your heart rate may be 10 or 20 beats per minute higher in the heat than under normal conditions, you should monitor it to make sure it doesn’t get too high.

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Cool Runnings

On the opposite end of the spectrum from heat training is cooling—another strategy that’s becoming increasingly important as endurance events get hotter and hotter. Performance tends to drop once core temperature climbs past 60 degrees Fahrenheit, and every degree hotter results in a .3 to .4 percent decline in performance, according to a 2021 study. Taking steps to manage your body heat can lead to major performance gains.

The Chasing 100 project took place in southern Italy in August, so the Adidas team had to account for heat. They pre-cooled athletes using frozen ice vests layered with reflective silver jackets—“basically a freezer bag around them,” says Makowski. Built-in fans blasted cold air over their bodies. The protocol lowered core temperatures by as much as seven degrees, and for some athletes, it took nearly two hours during the run for their body temp to rise to normal. “That’s a significant buffer to take into the race,” Makowski says. This cooling method, in particular, was effective because it covered a large portion of the body, according to a 2017 meta-analysis.

During the event, runners used custom-made neck sleeves filled with ice cubes. “Sibusiso went through about fifty during the event—the second he ran out of ice, he was throwing it away and got the next one,” says Makowski. 

Other athletes are adopting similar tactics. Jornet says he used an ice bandana to stay cool at the Western States 100-mile trail race in 2025, and recently used the same strategy during the cycling segments of his States of Elevation project, in which he climbed 72 peaks over 14,000 feet and covered 2,500 miles by bike in 31 days. “It was more about not getting into the red zone than maximizing performance,” he says.

But while elite athletes have access to custom cooling systems, experimental gear, and team support to keep ice from melting en route, the rest of us are resigned to commercial options. The neck is an effective place to cool the body’s core temperature, but it still may not be as powerful as cooling larger surface areas, says Wilkins. 

Koop says that’s the limitation with many consumer cooling devices, like headbands and palm coolers; they don’t cover enough area to meaningfully drop your core temperature. A 2024 study showed that the Omius headband only reduced forehead temperature, not heart rate or rectal temperature, during a 70-minute run. But these devices can make you feel cooler, which can elicit some performance benefits for short-term efforts, according to 2023 and 2024 studies.

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The Limits of Optimization

All these interventions might help the best athletes gain that final one percent, but they only matter if you’ve done the other 99, says Jornet. Overall health—low stress, good nutrition, sufficient sleep, high training volume—that’s what’s going to make the biggest difference for most people, he adds. 

“​​Endurance performance starts and ends with training,” says Wilkins. “You’re not going to get there with heat acclimation alone or by taking a bunch of bicarb.”

He’s seen it in his lab: “Even in elites, the biggest changes in hemoglobin mass happen in the first three or four months of structured training.” Other techniques might add a little bump, but the real gains come from consistency.

Jornet says his States of Elevation project taught him how important training adaptation is to reach your maximum potential. For 31 days straight, he spent up to sixteen hours a day climbing and cycling across the western U.S., tracking physiological markers like heart-rate variability and hormone levels each time he came down from the mountains. “After the third week, things started to stabilize,” he says. 

Amidst the extreme temperature swings, limited access to water, and near-constant physical strain, it wasn’t supplements or quick tricks that helped him complete one of the most impressive endurance feats in history. It was his body’s inherent ability to adapt to the work he put it through. 

Still, if tinkering with your training like a mad scientist keeps you motivated to grind through the long rides and runs, it’s worth a try.