Fundamentals · F03

Cellular Energy & Fuel Systems

How the body produces, stores, and deploys energy at the cellular level across different intensities and durations.

Core Concept

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The Three Energy Systems Explained Without the Noise

Your body doesn't run on a single fuel source — it runs on three overlapping systems that shift depending on intensity, duration, and what you've eaten. Understanding how they interact is the foundation for everything else in this pillar.

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The Full Picture

11 articles

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Why Short-Burst Energy Doesn't Scale

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Glycogen: The Primary Limiter You Don't Feel Coming

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Fat vs. Carbs: What Actually Happens Under Load

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Mitochondrial Density and Endurance Capacity

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Why Low Energy Often Starts at the Cellular Level

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Why You Start Strong and Fade

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Energy System Mismatch: Training vs. Reality

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Brain Energy Use and Mental Fatigue

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Why Mental and Physical Fatigue Feel the Same

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ATP Resynthesis: The Rate That Actually Limits You

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