Start Here · 6 min

The Human Fuel Station

Your Body Is a Hybrid Engine

Your body doesn't run on one fuel. It runs on a mixture.

Carbohydrate and fat help fuel movement. Protein supports rebuilding and adaptation. The mix changes depending on the intensity, duration, and demands of your activity.

Meanwhile, three overlapping energy systems work together to produce ATP—the immediate energy that powers movement.

Understanding how these systems work is the first step toward training them intelligently.

The Human Fuel Station infographic: carbohydrate, fat, and protein; fuel contribution across intensity from rest to sprint; and the phosphagen, glycolytic, and oxidative energy systems. — Movement IQ™ | FranklyFitness® Download Infographic

Take Control of Your Engine

Move the throttle. Watch how your body produces energy.

Throttle

Hike

Relative intensity: Moderate

These are example intensities, not universal classifications. A steep hike can be harder than a run.

Your fuel mix

Illustrative

You are always blending fuels.

CarbohydrateHigh-output fuel · ~50%

Muscle and liver glycogen, plus blood glucose.

FatEndurance reserve · ~50%

Vast storage, but slower maximal ATP rate.

Protein · Repair + Adaptation

Always needed to rebuild tissue and adapt to training. It can contribute energy, but it's not a primary exercise fuel in most situations.

Shares show carbohydrate vs. fat oxidation only. Fat's share can fall while total energy use rises.

Three energy systems

Relative emphasis

All three run at once. Only the emphasis shifts.

Immediate power · ~2%

Rapid energy · ~3%

Sustained energy · ~96%

Oxidative metabolism dominates, with carbohydrate and fat both supplying fuel.

ATP demand

Relative, not measured

Low

is your body's immediate usable energy currency. Your energy systems continually regenerate it — the tank doesn't simply empty. The faster the work, the faster ATP must be rebuilt.

What your body is doing · Hike

Depending on terrain and pace, your energy demand rises. Both fat and carbohydrate help power sustained movement.

Your body doesn't use one fuel or one energy system. It's constantly adapting its energy production to the demands of the task.

This interactive model illustrates general exercise-physiology principles. Actual fuel and energy-system contributions vary between individuals and activities.

Fuel sources are not energy systems.

Your fuel provides the resources. Your energy systems regenerate the ATP that powers movement.

We don't just do cardio. We train energy systems.

energy systemsfuelATPmetabolismconditioningcardiointeractive

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Move Well

Foundational mechanics for a body you can trust.

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