How High-Carb May Be Changing Training Theory

We’re in the most exciting moment in the history of endurance sports.

A few years ago, everyone started getting faster and more powerful. Now, nearly every course record is getting demolished at ultramarathons and marathons, world records are going down every week or two, and bike power numbers are going off the charts. 

It’s not just record-setters. At the Black Canyon 100k, the 5th place men’s time would have won all but two other years, and Riley Brady and Tara Dower both chopped miles off the previous times for women. The old collegiate mile record from just a few years ago wouldn’t even qualify for the NCAA champs in 2025. Mid-pack power numbers at the Tour de France would have competed for the top ten a decade ago.

Everything is changing, everywhere, all at once. I don’t think we’ll ever see a moment like this again, when what was previously considered marginal potential growth at best suddenly becomes an exponential growth curve with no end in sight. What gives?

I think that the biggest clue is that we’re seeing the change from the 800 meters and mile all the way up to multi-day events. What connects all of those distances? In my opinion, it’s the need to adapt to hard training week over week. And what’s causing athletes to adapt faster? It’s the explosion of high-carb approaches in training and racing (mixed with some combination of supershoes, bicarb supplementation, post-exercise ketones, heat, better training science, and a bigger focus on sports psychology).

Fueling adequately every single day of training reduces muscle damage, improves glycogen recovery, and causes the muscles to return to full strength more rapidly, while also potentially supporting the nervous system and endocrine system. What are the implications?

One of the most fascinating windows into the high-carb revolution is talking to athletes who straddled both generations. In the cycling peloton, athletes describe a fundamental shift in training approach and intensity, coinciding with enhanced mid-ride fueling. I have a unique little window since I coached lots of pro runners before and after the shift, and I apply the principles myself as an athlete. Therefore, I not only see the changes in performance, I see the theory shifting with it, and I feel the difference in myself. 

That feeling might be the most important element of all. In my own training, I’ve noticed that what might have previously been considered “undisciplined” or “risky” training actually feels totally sustainable when it’s done with a constant fueling emphasis. I’m hearing the same feedback from athletes who are surprised by how they feel relative to expectations built in a time before high-carb was the norm. 

As the ground shifted beneath the feet of all endurance sports, it led to a tricky conundrum. If athletes are responding differently to training, might that also change training theory altogether?

The jury is out on that question. But I think what we’re seeing across endurance sports is partially related to training theory catching up to healthier and stronger athletes who absorb stimuli differently than their predecessors. Here are four ways I’ve personally shifted my training theory for athletes who have dialed in their fueling needs.

One: Racing More Often

I used to tell athletes that they shouldn’t do more than two 100 milers in a year, and even that was reserved for freakish adapters who were experienced at the distance. In 2024, at 36 years old (an age when recovery rates were assumed to be slower in the lower-carb prehistoric times), I personally ran the Leadville 100 Miler and Javelina 100 Miler just 10 weeks apart as my first cracks at the distance, and 10 weeks after that I was back to being faster than ever at short events. What we used to assume about breakdown from hard training and racing is starting to shift, and the acute stresses of race day are coming on top of less chronic stress, particularly to the endocrine and nervous systems, which are given a protective blanket by carb intake during exercise. 

Now, I think that hard races are often just fantastic super-compensation stimuli. Training theory always assumed middle-distance runners could race a lot and continue improving. Now, I think marathons are playing like middle-distance events, and ultras are playing like marathons. The races are making athletes stronger, rather than tearing them down and leading to longer rebuilds.

Two: More Very Hard Workouts

The same rationale applies to training. Let’s zoom in using a 2020 study that helped launch the high-carb revolution in trail running. The study had 26 elite runners consume 120g, 90g, or 60g of carbs per hour in a mountain marathon with 4000 meters of vert. A day later, the runners were tested for various power and performance variables, and the highest carb group had lower fatigue and lactate, and far better performance at the tests. 

Obviously, a race is the hardest possible workout, and conventional wisdom might have shied away from very hard sessions because they would reduce performance in subsequent days, cause chronic stress that diminishes subsequent training response, and increase injury risk. This study shows what high carb can do--it can help athletes absorb hard sessions much more rapidly. Because injury and adaptation are a part of the same spectrum, that should reduce injury rates too. And we know that carbohydrate availability improves bone density and healing.

Harder sessions still probably shouldn’t be the standard. Injury risk may still be high, and excessive volume or intensity will still backfire. But I know that as a coach if an athlete is fueling well during their workouts, I’m much less scared to push an athlete to the edge.

Three: Higher Quantities of Z2 Training

In cycling, Tadej Pogacar is notorious for his multi-hour Z2 rides where he’s pushing 320+ watts in aerobic zones. The old “easy days easy/hard days hard” framework has gotten more complicated as athletes are able to push high power on the bike and run for much longer since high carb becomes essential with that type of work. If previous generations tried a Tadej-style day, it would just become a hard workout that would take away from the remainder of the training. Now, it can be another brick in the wall.

In the old days, there were coaching systems that did lots of relatively high-power/speed for aerobic work, but those systems often caused injuries or selected for adaptation freaks, throwing tons of eggs at the wall and hoping one or two wouldn’t break. Now, it seems like the high carb is turning tons more athletes into adaptation freaks who can absorb more steady volume, not just purely easy volume. We are all becoming more like the unbreakable eggs.

Four: More Fatigue Resistance/Durability Efforts

I also see athletes being able to maintain running economy or bike power later in training days, possibly leading to better responses to hard efforts after the accumulation of 1000-2000+ kJ of work. A 2016 review found that carbohydrate ingestion reduced central fatigue, a primary performance limiter on longer days. A 2024 study took it a step further, finding that pro cyclists who performed better late in events were better able to access carb oxidation than those who performed worse. My coaching theory is that there may be an outsized benefit to training the body to access carb oxidation with high output at the end of long days, which requires tons of carbs on board to actually lead to high performance. An example might be as simple as 6 x 30-second hills or 5 minutes hard near the end of a long run or bike. Carbs make fatigue resistance practice much more effective.

The wild part about coaching in 2025 is that we are all riding a wave of performance, and there’s no telling when it might reach its apex. With how much performances are skyrocketing across the endurance landscape, I think training theory is faced with an ultimatum: adapt or die. I just wish I could zoom forward five more years to see all of the ways that I’m wrong now so that I could adapt sooner.

Thankfully, we know that carbs help with adaptation.

Photo Credits: Bare Photography