Anaerobic metabolism
Energy production without oxygen — fast, limited in capacity, and costly to sustain.
Anaerobic metabolism covers the two oxygen-independent routes to ATP: the creatine phosphate system for the first seconds, and anaerobic glycolysis for efforts up to a couple of minutes. Both are fast and both are limited, either by a small store or by the accumulation of metabolites.
It matters because maximal efforts depend on it entirely — no aerobic system can supply ATP quickly enough for a sprint start or a maximal lift. Its capacity is trainable, largely through better buffering and better tolerance of the acidic environment hard glycolysis creates.
In practice the old framing of aerobic and anaerobic as separate gears is misleading. Both run continuously, and intensity simply shifts the proportion; the useful question is which one is limiting at the effort you care about.
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Written and reviewed by Mathew Beale, MSc Biotechnology, University of Reading.
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