How protein works for endurance athletes
Runners think protein is for lifters. Their muscles disagree around kilometre 25.
Endurance athletes need roughly 1.2 to 1.4 g/kg/day, well above the sedentary reference intake, and chronically eat less than that because the culture is built around carbohydrate.
How your body actually uses it
Two things happen on a long session. Once glycogen runs low, amino acids are oxidised for fuel, and the branched-chain three in particular are burned directly in working muscle. That is protein leaving the building as energy.
Meanwhile the training itself is a remodelling stimulus: more mitochondria, more capillaries, more of the enzymes that make aerobic metabolism work. Every one of those adaptations is protein synthesis. Endurance training is not a low-protein activity. It is a high-protein activity that has been culturally filed under carbohydrate.
What most people here get wrong
Protein neglect
The base assumption that protein is a strength-sport concern. It leads to a diet built entirely around fuelling, with recovery treated as an afterthought.
Assuming carbohydrate alone drives recovery
Carbohydrate replaces glycogen. It does not rebuild anything. The adaptations you actually train for are protein, and they need amino acids.
Cutting protein during heavy blocks
Requirements are highest exactly when volume is highest, which is also when appetite is strange and meals get skipped. This is the worst possible time to under-eat protein.
The amino acid angle
Oxidising branched-chain amino acids during long efforts raises the bar slightly on quantity, and post-session feedings with a complete profile support the remodelling the session just asked for.
There is a point here that runs against intuition, so it is worth stating outright. Training raises your protein target. It does not raise your amino acid requirements. The nine requirement lines in AminoLens are WHO body-weight figures, and the app deliberately does not scale them by activity or goal, because inflating them would invent a standard that does not exist. So training changes the quantity question, and the Sankey keeps telling you the truth about the mix either way.
The playbook
- Set the endurance activity level and the app targets 1.4 g/kg/day, the top of the commonly cited 1.2 to 1.4 band, on the reasoning that endurance athletes chronically under-eat protein.
- Put protein into post-ride and post-run refuelling. The classic 3:1 or 4:1 carbohydrate-to-protein recovery ratio is a reasonable default.
- Spread feedings across the day rather than backloading them onto dinner after an evening session.
- If you are plant-based, watch lysine like every other plant-based athlete. Endurance does not change which line runs short first.
Where AminoLens comes in
Setting endurance as your activity level raises your daily protein target to 1.4 g/kg and leaves the nine amino acid requirements where WHO put them. That asymmetry is deliberate, and the app will show you both halves.
See where your own protein goes
One photo. All nine lines. The one that is holding the rest back.
Analyse a meal