AdrenalineEpinephrine
The fight-or-flight hormone that raises heart rate and mobilises fuel.
Adrenaline is released from the adrenal medulla in response to sympathetic activation. It raises heart rate and contractility, widens the airways, redirects blood to working muscle, and mobilises glucose from the liver and fatty acids from fat stores.
It matters because it is the acute performance hormone. It underlies the surge that lets someone lift more in competition than in training, and it is the main driver of fat mobilisation during exercise — which is the actual mechanism behind most stimulant-based fat-loss claims.
In practice it is also why caffeine and pre-workout stimulants work, and why they stop working well when used constantly: the system downregulates. Adrenaline is also the emergency treatment for anaphylaxis, given by auto-injector.
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Written and reviewed by Mathew Beale, MSc Biotechnology, University of Reading.
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