Substrate & fuel availability
One of 4 mechanistic pathways to 🏃 Endurance & work capacity · 9 options
Glycogen depletion is the classic wall. Metabolic flexibility — being able to run on fat when carbohydrate runs out — is what pushes it further away, and it is trainable and partly pharmacological.
Metabolic flexibility — the ability to run on fat when carbohydrate runs out — tracks with insulin sensitivity. If HbA1c is creeping up, you are glucose-dependent, and that is the wall you keep hitting.
Carnitine, Total and FreeHbA1c (Hemoglobin A1c)Lipid Panel (Cholesterol, HDL, LDL, Triglycerides)Free T3 (Triiodothyronine)🍭 Metabolic Health & Prediabetes covers these in one panel →
What engages this pathway
Ordered by how directly each one acts on the mechanism above — never by how much trial evidence exists. Each links to its full breakdown with dosing, half-life and vendor.
🧬 MCT Oil
Rapidly oxidised medium-chain fats that bypass the carnitine shuttle entirely. Provides fuel without competing for gastric emptying with carbohydrate.
🧬 L-Carnitine L-Tartrate
Carnitine reduces muscle damage markers and may improve fat oxidation. The absorption problem is real — muscle carnitine only rises meaningfully when co-ingested with a substantial carbohydrate insulin spike.
🧬 Acetyl-L-Carnitine
Crosses the blood-brain barrier, so the argument here is central fatigue as much as peripheral substrate.
💉 Meldonium
Shifts metabolism from fat to glucose oxidation, which is more oxygen-efficient per unit ATP. Effective enough that it was added to the banned list after a wave of positive tests — the mechanism is not in doubt, the legality is.
💉 L-Carnitine
Injectable carnitine sidesteps the absorption ceiling that limits the oral form.
🧬 Peak ATP
Extracellular ATP signalling raises blood flow and has trial data for training volume.
🧬 Essential Amino Acids
Reduces central fatigue by limiting the tryptophan-to-serotonin rise that accompanies BCAA depletion in long efforts.
🧬 Whey Protein (RecoveryPro)
Post-session protein accelerates glycogen resynthesis when carbohydrate is submaximal, and repairs the damage.
🧬 Beetroot (Nitrates)
Beyond NO, nitrate appears to improve mitochondrial efficiency — more ATP per oxygen consumed.
The other 3 routes to endurance & work capacity
Pick the pathway that matches where you are actually stuck. An appetite drug does nothing for someone who already undereats.
Want the protocols behind these?
Dosing schedules, stacking, cycle timing and Coach Cam's notes live inside the Academy — plus the full interactive Vault.
Join the Academy — $10/mo →← Open this pathway in the interactive Vault
Frequently asked questions
Glycogen depletion is the classic wall. Metabolic flexibility — being able to run on fat when carbohydrate runs out — is what pushes it further away, and it is trainable and partly pharmacological.
9 options are mapped to this pathway in the Vault, including MCT Oil, L-Carnitine L-Tartrate, Acetyl-L-Carnitine, Meldonium. They are grouped by the mechanism they act through rather than ranked by how much trial evidence exists — 7 carry clinical validation and 2 are mechanistic predictions.
Metabolic flexibility — the ability to run on fat when carbohydrate runs out — tracks with insulin sensitivity. If HbA1c is creeping up, you are glucose-dependent, and that is the wall you keep hitting. The markers worth checking are Carnitine, Total and Free, HbA1c (Hemoglobin A1c), Lipid Panel (Cholesterol, HDL, LDL, Triglycerides), Free T3 (Triiodothyronine).
Unproven is not the same as ineffective. Of the 9 options on this pathway, 7 have clinical validation and 2 are graded theoretical — meaning the mechanism is sound but the specific human trial has not been run, which is true of a great deal of what works in this space. Nothing on this page is ordered by evidence tier, because sorting by trial count would bury the compounds you came looking for.