Exercise Physiology: From Muscle Action to Glucose

Start with muscle action and trace backwards to discover where the energy comes from. At each step, ask: "What does this need?" — and follow the chain all the way back to glucose. Click any active module to explore its interactive visualization.

ATP powers the cross-bridge cycle — the sarcomere attempts to shorten

← ATP

ATP exported from mitochondria to the cytoplasm

← ATP

Proton flow spins a molecular turbine to forge ATP

← H⁺ gradient

Electrons flow, pumping H⁺ across the membrane

← NADH, FADH₂

Acetyl-CoA oxidized, generating NADH + FADH₂ for the ETC

← Acetyl-CoA

Pyruvate → Acetyl-CoA + CO₂ + NADH — the irreversible one-way gate

← Pyruvate

Glucose to pyruvate & lactate — 2 ATP + 2 NADH + NAD⁺ recycling

ATP Yield: One Glucose → ~30-32 ATP

Glucose → 2 Pyruvate + 2 NADH

(substrate-level)

→ 2 Pyruvate

PDH Complex ×2

2 Pyruvate → 2 Acetyl-CoA + 2 NADH

(via 2 NADH → ETC)

→ 2 Acetyl-CoA

Krebs Cycle ×2

6 NADH + 2 FADH₂ + 2 GTP

(2 GTP, substrate-level)

→ 10 NADH, 2 FADH₂

ETC + ATP Synthase

10 NADH → ~25 ATP, 2 FADH₂ → ~3 ATP

(oxidative phosphorylation)

Total per glucose: ~30-32 ATP

Fat fuels — the spiral that clips 2-carbon units off fatty acids, feeding acetyl-CoA, NADH & FADH₂ into Krebs & ETC.

Metabolic Profile

The big picture — see how fat, carbs, lactate, and H⁺ change as exercise intensity rises. Ties all modules together.

Foundational glossary — redox, electron carriers, energy currencies, and the concepts that connect every module.

Lactate Shuttle

George Brooks' paradigm shift — lactate is fuel, not waste. Watch it shuttle between glycolytic and oxidative cells via MCT transporters.

Fatigue Mechanisms

Why muscles fail — watch H⁺, Pi, Ca²⁺, and K⁺ accumulate to degrade force production in real time. Not lactate.

Reverse Engineering the Energy Pathway

Every muscle action consumes ATP — but where does that ATP come from? Trace backwards through the chain: the Sarcomere needs ATP, which is forged by ATP Synthase, which is driven by a proton gradient built by the electron transport chain, fuelled by carriers from the Krebs Cycle, which starts with pyruvate from glycolysis. Each module lets you interact with one stage, controlling the inputs and watching the outputs in real time.