The Consequences Of Delaying Carbohydrates After Your Run

Delaying Carbohydrate Intake After Exercise Impairs Next-Day Performance

Most athletes know that carbs are crucial for performance, but what happens when you skip them after a workout? Recent research suggests that delaying post-exercise carbs could actually impair your recovery and next-day performance, despite the belief that glycogen stores can be replenished later. Even if you’re not training again the same day, the so-called “anabolic window” might be more important than you think—especially for fast recovery.

Most high-performing athletes realize the utility of carbohydrates for performance.

Whether pre-workout or intra-workout, carbohydrates improve intermittent (high-intensity) performance, long-duration endurance exercise, and even strength- and power-related performance.​

But why?

Carbohydrates (really, glucose) are one of our body’s primary fuel sources, the others being fat and, to some extent, ketones. They’re our primary fuel source at higher exercise intensities.

We don’t need to eat carbohydrates to perform. Our body stores the carbs we’ve eaten previously as glycogen, and we have enough of it to last 90–120 minutes or more of moderate-intensity exercise. Hence, working out fasted in the morning doesn’t feel so bad. Nevertheless, consuming carbohydrates before working out tends to have some benefit, perhaps by providing a quick and readily usable source of fuel.

​Skeletal muscle energy metabolism during exercise​

Carbohydrates also improve performance via some mechanisms involving the central nervous system. Our body and brain can sense when we’ve ingested glucose and respond by allowing us to push a bit harder, or so the thinking goes. This is why just swishing a carbohydrate-laden drink in your mouth without actually swallowing it also improves performance. Try that during your next workout.

Ok—carbs are good before and during exercise. But what about after?

The primary reason to consume post-exercise carbohydrates is to replenish muscle glycogen. Our glycogen stores can drop by 20–40% after long-duration or high-intensity exercise, and we need to replace what we’ve lost. This is true if you’re going to be training the next day, and especially true if you’re going to be training again on the same day.

Common sense has it that consuming carbs as soon as possible after exercise is best. There’s an “anabolic window” for carbs (the same one doesn’t appear to exist for protein) during which our body is more sensitive to nutrient intake. Glycogen replenishment seems to be enhanced the sooner we take in carbs after a workout, among other effects. Restricting carbs during training (before and likely after) also appears to impair markers of bone health—several reasons to kick-start the recovery process with carbohydrates as soon as possible after training.

However, some athletes practice carb restriction after exercise, waiting several hours or more before consuming their first carbohydrate-containing meal. There’s a good reason for this: some studies show that this method can enhance certain aspects of metabolism, endurance adaptations, and mitochondrial biogenesis. It’s like fasted training extended to the post-workout period. It’s also thought that as long as you’re not exercising again on the same day and consuming enough carbohydrates during the ensuing ~24 hours, your muscle glycogen stores will be fully replenished by the next time you exercise again. By this logic, there’s no need to think about nutrient timing after exercise.

According to a new study, however, we might want to rethink this practice. If we don’t take advantage of this post-exercise window of opportunity, we may compromise our recovery and limit our performance the next day.

But it might not be for the reasons you think.

The study, published in Acta Physiologica, aimed to investigate the effects of immediate versus delayed carbohydrate intake after exercise on molecular responses, muscle glycogen levels, and next-day exercise capacity.

Nine recreationally active men (mean age 24 ± 2 years) participated in the study. These individuals were healthy, non-smokers, and exercised for more than 150 minutes per week but did not follow a structured training program.

The participants performed a high-intensity exercise on a cycle ergometer, consisting of 10 × 2-minute intervals at ~94% of peak aerobic power (225 ± 39 watts), with 1-minute rest periods between intervals. The exercise intensity was calculated based on each participant’s peak power and lactate threshold from a previous graded exercise test.

Immediate condition: In the immediate carbohydrate condition, participants consumed 2.4 g/kg of carbohydrates (via a commercial drink) within the first three hours post-exercise, administered in small boluses every 20 minutes.

Delayed condition: In the delayed carbohydrate condition, participants consumed only water during the first three hours post-exercise and then consumed the same amount of carbohydrates as in the immediate condition, starting at three hours post-exercise.

Muscle biopsies were taken at several time points: pre-exercise, immediately post-exercise, and at +3 h, +8 h, and +24 h during the recovery period. These were used to assess muscle glycogen content, protein abundance, and phosphorylation (e.g., p-AMPK, p38MAPK), and whole-muscle mRNA content for genes associated with mitochondrial biogenesis and metabolism (e.g., PGC-1α, UCP3, PPARs).

The trials were matched for total carbohydrate intake—a crucial point. Along with the post-exercise nutrition, the participants consumed a standardized, high-carbohydrate diet (~7 g of carbohydrate/kg/day) during the 12 hours preceding the exercise session and throughout the 24-hour recovery period.

After 24 hours, participants performed another high-intensity exercise session to task failure, aiming to assess next-day exercise capacity. The same intensity was used as in the initial exercise session, but in this one, the participants completed as many intervals as possible. Heart rate, perceived exertion, and blood lactate were also assessed during exercise.

Results
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Molecular Responses

Contrary to the hypothesis, delaying carbohydrate intake did not significantly enhance exercise-induced molecular responses (e.g., AMPK, PGC-1α, p38MAPK) related to mitochondrial biogenesis or metabolism during the 24-hour recovery period. An interesting finding because, as I discussed earlier, this is one of the main reasons to delay carbohydrate intake (or partake in fasted exercise).

Muscle glycogen

Muscle glycogen was reduced by 36% immediately post-exercise in both conditions and remained lower at +3 h (22–27%) and +8 h (11–14%). By the start of the next exercise session, 24 hours later, muscle glycogen returned to near-baseline levels in both conditions.

Although there were some minor fluctuations, such as a significant difference between +3 h and +24 h, the overall glycogen resynthesis rates were similar between the two conditions.

Exercise Capacity

Delaying carbohydrate intake reduced next-day high-intensity interval exercise (HIIE) capacity and increased perceived effort, despite no differences in muscle glycogen recovery or molecular responses between the two conditions. On average, participants completed 30% fewer intervals in the delayed carbohydrate condition compared to the immediate carbohydrate condition.

Perceived exertion (RPE) WAS also significantly higher (~2 units) in the delayed condition during the subsequent exercise test, indicating participants felt the exercise was more challenging. Although heart rate and blood lactate levels increased during the next-day exercise session, no significant differences were found when comparing delayed and immediate intake.

What this means for runners

If you care about showing up ready to go the next day, don’t wait around on carbs. This study shows that even when glycogen levels “catch up” after 24 hours, delaying post-exercise carbs still hurts next-day performance—suggesting there’s more going on than just glycogen. Maybe it’s the nervous system, maybe it’s whole-body recovery, but the practical takeaway is simple: get carbs in soon after you finish. Pair them with protein (and some fat) to cover all your bases. You don’t need to slam a gel the second you stop running, but try to have a real meal or substantial snack within 30–60 minutes.

The extra attention to timing could mean the difference between feeling sharp and resilient in your next workout versus slogging through. For runners who stack workouts close together or train daily, this window matters even more.

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