05/20/2026
Endurance athletes get told to eat more protein.
Almost no one tells them why, or how much of which amino acid actually matters.
So here’s the short version of two months of Science Wednesdays.
During a hard session you burn carbs, fat, and amino acids. Leucine in particular. And those amino acids don’t come from your last meal — they come from your own muscle. Past about 90 minutes, the math stops being trivial. Breakdown outpaces rebuilding, and protein balance during the session turns negative. That isn’t damage. It’s the metabolic cost of training.
The moment you stop, something changes.
In a one-legged cycling study, the working leg showed mTOR up roughly 60% and p70S6K up about five-fold compared to the resting leg in the same person. They called it anabolic sensitization — exercise primes muscle to rebuild.
But priming isn’t building. When researchers fed protein during recovery instead of leaving subjects fasted, the rebuilding signal got louder, and muscle protein synthesis climbed higher.
The next question got narrower. Was it the protein, or one piece of it?
Pasiakos and colleagues gave cyclists two drinks — same calories, same total essential amino acids — differing only in leucine. 1.87 grams versus 3.5. The higher-leucine drink produced about 33% more muscle protein synthesis. Leucine wasn’t along for the ride. It was the trigger.
Then the dose-response work came in. Different labs. Different proteins. Different study designs. The number kept landing in the same place: about 3 grams of leucine, usually packaged in roughly 30 grams of high-quality protein. When researchers fortified a plant protein blend to 3 g leucine, the response was indistinguishable from whey.
None of this is about magic. It’s about a system that turns on, briefly, after a hard session. It has a switch. The switch responds to a specific thing.
For endurance athletes — short windows, frequent sessions, suppressed appetite after hard work — leucine density is the lever.
Not total protein. Density.
Recovery isn’t passive. It’s chemistry. And the chemistry has a number.
That’s the number we built Addra around.
References on the last slide.
