What if the difference between a good workout tomorrow and a bad one comes down to what you do in the two hours after today's session?
For decades, endurance athletes have been told the same thing after hard training: Eat carbs - lots of carbs. There has been a bit of discrepancy in the quality and formats those carbs might be delivered in, but the age-old story has been to prioritize carbs and a 3:1 ratio of carbs and protein. There's even some great old videos on YouTube that many of you may have grown up with, where Ryan Hall (one of the fastest marathoners in American history, with a PB of 2:04) touted the importance of carbs post-workout, eating lots of simple sugars like gummy worms and candy immediately after ripping sub-9-minute 2-mile repeats like clockwork.
In one interview, he specifically mentioned keeping a pile of fat-free candy in his gym bag and eating it after workouts, because, in his words, marathon nutrition is largely simple carbohydrates anyway, so he might as well choose ones he enjoys.
And to be fair, that's not entirely the wrong way to go about things. Recovery does start post-session immediately, and some of the greatest in the world aren't thinking about diving into their Strava graphs and HR metrics while they couch rot post-ride; no, they're thinking about their long run the next day, and how they can show up for it.
After a long ride, a brutal swim set, or a run that leaves your legs feeling like concrete, glycogen stores are obviously depleted. Carbohydrates are the fastest way to begin replenishing that fuel and preparing for the next session. But what if glycogen isn't the only thing that matters?
That's exactly the question researchers at the Norwegian School of Sport Sciences wanted to answer. Their findings suggest that carbohydrates alone may not be enough to maximize recovery between hard endurance sessions, and that adding protein may improve next-day performance more than many athletes realize.
A Study Designed to Break Athletes
The Norwegian researchers recruited eight elite male cyclists - not recreational athletes, or weekend warriors - no, these were elite cyclists with an average VO₂max of 74 ml/kg/min - numbers that place them firmly in the high-performance category.
The protocol was simple:
Ride hard enough to completely deplete yourself. Recover. Race again the next day. (Sounds kind of awesome, right?)
Athletes completed prolonged cycling at approximately 73% of VO₂max before performing repeated one-minute efforts at 90% VO₂max until exhaustion. In other words, this wasn't a casual Z2 ride.
To put this into more concrete numbers that you might grasp a bit better than "73% of VO₂max" - for elite cyclists, that percentage is roughly equivalent to 4.8 to 5.3 W/kg, so...for different rider sizes, it would look like the following:
| Rider weight | 73% VO₂max | 90% VO₂max |
|---|---|---|
| 65 kg | ~310–345 W | ~390–435 W |
| 70 kg | ~335–370 W | ~420–470 W |
| 75 kg | ~360–400 W | ~450–500 W |
So, yeah - this was a genuine depletion session designed to create the kind of fatigue endurance athletes experience during hard training blocks, stage races, training camps, and race weekends.
The Recovery Experiment
Immediately after exercise, athletes were assigned to one of two recovery strategies:
Group 1: Carbohydrate Only
- 1.2 g carbohydrate per kilogram of bodyweight per hour
- No protein
Group 2: Carbohydrate + Protein
- 0.8 g carbohydrate per kilogram per hour
- 0.4 g whey protein per kilogram per hour
Importantly, total calories were matched. This wasn't a situation where one group simply ate more food. Researchers controlled the entire diet for the following 18 hours, ensuring the only meaningful difference was the addition of protein during the early recovery period.
The next morning, athletes returned to perform:
- A cycling time trial
- A maximal 10-second sprint
The Results Were FAR From Subtle
The carbohydrate-plus-protein group outperformed carbohydrate alone in every performance measure.
Time trial performance improved by:
8.5%
(41:53 versus 45:26)
Sprint power improved by:
3.7%
(1,063 watts versus 1,026 watts)
Perhaps even more interesting:
Every single participant performed better following the carbohydrate-plus-protein recovery strategy. Not most athletes. Not the average athlete.
Every athlete.
That's a remarkable finding in sports science, where individual responses often vary dramatically.
Why Would Protein Matter If Glycogen Is Being Refilled?
This is where the study gets particularly interesting. The traditional recovery narrative focuses almost entirely on glycogen restoration, and, yeah, glycogen absolutely matters.
But exhaustive endurance exercise doesn't just drain fuel stores - it also increases muscle protein breakdown. After a hard session, your body enters a catabolic state. Carbohydrates can begin restoring glycogen, but they don't necessarily stop the ongoing breakdown of muscle proteins.
Protein provides the amino acids required to:
- Reduce muscle protein breakdown
- Support muscle protein synthesis
- Accelerate tissue repair
- Shift the body toward a more anabolic recovery state
The result? Athletes may arrive at the next session with muscles that are structurally better recovered—not simply refueled.
The Nitrogen Balance Story
One of the most revealing measurements in the study was nitrogen balance. Think of nitrogen balance as a snapshot of whether the body is building or breaking down tissue.
The carbohydrate-only condition produced a strongly negative nitrogen balance:
−82.4 mg/kg
A clear sign of ongoing catabolism.
The carbohydrate-plus-protein condition produced a neutral-to-positive nitrogen balance:
+7.0 mg/kg
In practical terms, adding protein helped athletes transition out of the breakdown phase and into recovery much faster, and the next day's performance reflected that difference.
The Protein Dose Wasn't Extreme
One of the most useful takeaways is that the successful protein intake wasn't some absurd bodybuilder-level protocol.
Total daily protein intake ended up around: 1.83 g/kg/day
This aligns almost perfectly with modern recommendations for endurance athletes during periods of heavy training.
For an athlete weighing:
- 60 kg → ~110 g/day
- 70 kg → ~128 g/day
- 80 kg → ~146 g/day
These numbers are increasingly supported by current sports nutrition literature. They are, profoundly, also supported by our protein calculator. Have you tried this out yet? Click here to dial in your own optimal protein guidelines.
What This Means for Endurance Athletes
If you're training once per day and have plenty of recovery time between sessions, the difference may be relatively small.
But if you're:
- Training twice per day
- Completing back-to-back hard sessions
- In a race week
- At training camp
- Preparing for a stage race
- Recovering during a heavy training block
Protein becomes far more important because recovery isn't just about replacing fuel; rather, it's about rebuilding the athlete. The faster you can stop the breakdown process and begin repair, the better prepared you'll be for the next session.
The Honest Science
This study isn't perfect. The sample size was small. Only eight athletes participated. All were elite male cyclists.
That means we should be cautious about applying the exact numbers universally.
However, the study also had several major strengths:
- Randomized
- Double-blind
- Crossover design
- Fully controlled diets
- Elite athlete population
- Consistent positive response across all participants
Taken together, it's one of the stronger pieces of evidence supporting protein intake during recovery from exhaustive endurance exercise.
The Addra Takeaway
After a truly hard workout, carbohydrates are necessary, but they may not be sufficient in isolation.
The evidence suggests that combining protein with post-exercise carbohydrate intake helps athletes recover more completely, preserve muscle integrity, and perform better the next day.
For endurance athletes chasing consistent training, not just isolated workouts, that distinction matters.
Evidence-based targets (if you only remember ONE part of this blog, this is the part to mentally hit the save button on, or send to a friend)
- ~0.4 g protein/kg during the first two hours after exercise
- ~1.8–1.9 g protein/kg/day during heavy training blocks
- Prioritize high-quality, leucine-rich protein sources
- Combine protein with carbohydrate rather than choosing one or the other
Because the goal isn't simply to refill the tank - it's to rebuild the engine!
References
Sollie O, Jeppesen PB, Tangen DS et al. Protein intake in the early recovery period after exhaustive exercise improves performance the following day. J Appl Physiol (1985). 2018 Dec 1;125(6):1731-1742.
Kato H, Suzuki K, Bannai M, Moore DR. Protein Requirements Are Elevated in Endurance Athletes after Exercise as Determined by the Indicator Amino Acid Oxidation Method. PLoS One. 2016 Jun 20;11(6):e0157406.
Witard OC, Hearris M, Morgan PT. Protein Nutrition for Endurance Athletes: A Metabolic Focus on Promoting Recovery and Training Adaptation. Sports Med. 2025 Jun;55(6):1361-1376.
