The Year-Round Adaptation Revolution

Carbs are driving a significant part of the performance revolution in endurance sports. And I don’t think the primary driver is race-day fueling. Instead, I think the biggest benefit comes from recovery and adaptation.

Here’s the type of hypothetical that I like to propose to athletes to help them buy into the carb science. Today, imagine you’re going on a 2-hour moderate run. Tomorrow, you have to run a 5k race. And a villain from a 1980s Bond movie is laughing maniacally, saying that you better perform at your best in the race or it’s a one-way ticket to vaporization town. How do you fuel today?

The answer is that you slurp carbs before, during, and after the 2-hour training day.

Making the stakes extreme underscores a point that many athletes look past: every day in hard training, we are playing a high-stakes game with recovery and adaptation. It’s not about putting in the work. It’s about adapting to the work we’re putting in. Yet so many athletes ignore the science and real-world evidence showing that fueling training is the easiest way to enhance adaptation

A 2024 study had 9 male athletes complete a double-blind crossover design consisting of 10 x 2 minute intervals on day 1 and standardized carb intake across the day at 7 g/kg bodyweight. However, in one of the trials, the athletes had none of those carbs 0-3 hours after training, whereas they had 2.4 g/kg in the other trial. On day 2, the athletes did 2 minute intervals to failure.

Here’s the money quote: “Delaying carbohydrate intake reduced next-day capacity (5 ± 3 intervals) and increased RPE (~2 ratings), despite similar physiological responses between conditions.”

In other words, without post-exercise carbs, the brain and body hit the “off” switch earlier on subsequent days because it feels harder. That would likely correspond to worse adaptation to the first session, and worse performance on future sessions.

A pair of studies from 2020 (here and here) show part of the physiology that might be driving the performance reductions. Both studies looked at male runners completing a trail marathon, and it split them into three groups: 60 grams of carbs per hour (what athletes usually do on race day), 90 grams of carbs per hour (new recommendations for most athletes), and 120 grams of carbs per hour (high-carb fueling). 

Higher carb intake resulted in lower exercise load (less stress on the body), lower creatine kinase (reduced muscle breakdown), lower lactate dehydrogenase (less fatigue). The reduced exercise-induced muscle damage in higher-carb athletes led to higher performance 24 hours post-event. You can imagine how much a 30 gram per hour group would be screwed, let alone a no-carb group.

Now picture what happens over time as these types of studies are applied to the daily training process, particularly hard workouts and long runs. The athletes who are fueling better will perform better, adapting day-over-day so that outsiders might think it’s talent or training structure, when in reality it’s carbs. 

In practice, that doesn’t mean you need to be slurping 120 grams of carbs on every easy run. Instead, it means that you need to fuel the work you’re doing in training in order to adapt and stack up that training over time. Training without adequate carbs on board is like punching a hole in the hull of a ship, having to waste your time scooping out the water rather than going forward to new lands. 

Here are 3 rules that I apply:

• On all runs over 1 hour, start thinking about carb intake at 60+ grams per hour totals on most days (but it’s ok for male athletes to sometimes go lower on easy days if they are recovering and adapting well)

• On moderate long runs over 90 minutes or hard interval days over 1 hour, aim for 75-90+ grams of carbs per hour to enhance both performance and recovery

• Make sure that you have solid carb intake in the 1-2 hours after finishing any run that has high glycogen demands (which is almost every run)

A decade ago, I’d do a 2-hour moderate run with a gel and a flask of water, like my ultra heroes were doing. Now, I look at that and cringe with sadness for all of those years where I thought my potential was lower than it was.

Today, I’ll typically do a 2-hour moderate run with 3 x Science in Sport Beta Fuel Gels, 1 x Precision 100 mg Caffeine Gel, and 2-3 bottles of Skratch Hydration Mix (and/or Precision 1000 mg electrolyte tabs).

In related news, I’m 36 and I’m getting faster and stronger than ever. 

Carbs aren’t everything—you still need to work hard. But carbs are essential to adapt hard.

Photo Credits: Cody Bare