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Anaerobic glycolytic system (lactic)

The engine for hard efforts that last longer than a few seconds — a 400 m run, a 30–60 s set, repeated hard intervals. It breaks glucose down without oxygen, producing ATP quickly but not cleanly. Its byproduct (and the hydrogen ions that come with it) is what makes muscles burn and eventually forces you to slow down.

Relative power output over time power → 0s10s30s1m2m5m+ATP–PCrGlycolytic — this pageOxidative

Every all-out effort recruits all three systems at once — this shows which one dominates as the seconds tick by.

The metabolic pathway — where the energy comes from

FATS · triglycerideCARBOHYDRATEPROTEIN Fatty acids + glycerolGlucoseAmino acids Glycolysisnet +2 ATP · fast Pyruvate Lactateno O₂ → fatigue ↑ Cytosol (sarcoplasm) — no oxygen needed↓ Mitochondria — needs oxygen (O₂) β-oxidation Deamination→ into glycolysis or Krebs Acetyl-CoA Ketone bodies Krebs cyclecitric-acid cycle Electron transport chain ⚡ ATP Creatine phosphate → ATPinstant · 0–10s · skips the mill
The metabolic mill — how each fuel is broken down and fed into ATP. Lit path: the anaerobic glycolytic system.

Duration: ~10 seconds to ~2 minutes · Intensity: High (but sub-maximal) · Fuel: Glucose from blood and muscle glycogen · Oxygen: Not required (anaerobic) — runs faster than oxygen can be delivered

How it works

  1. Glucose (or glycogen) is split through glycolysis into pyruvate, netting 2 ATP per glucose (fast, but low yield).
  2. Without enough oxygen, pyruvate is converted to lactate to regenerate NAD⁺ so glycolysis can keep running.
  3. Lactate itself is a usable fuel — but the accumulating H⁺ ions lower muscle pH (acidosis), impairing contraction.
  4. This 'burn' rises until power output drops or the effort ends; lactate is then shuttled to heart, liver and other muscle to be reused or reconverted to glucose (Cori cycle).

What it powers

Byproduct: Lactate + hydrogen ions (H⁺). Lactate is a fuel, not the villain — the H⁺ acidosis is what limits the effort.

Recovery: Clearing lactate and restoring pH takes minutes; active recovery (light movement) clears it faster than sitting still.

Training: Trained with hard intervals of 30 s–2 min and incomplete rest (classic 'lactate tolerance' work), and with moderate-rep resistance training.