Same 20 seconds every time. Training and competition.

One fixed 15–30 s routine before every max attempt or round: one slow breath, picture it, say the cue word, one physical trigger. Keep it identical in training and competition. Having a routine matters more than which one.
S Evidence: strong. Large trials or many studies, pointing the same way.
Rupprecht et al. 2021 (meta-analysis, 112 effect sizes).
Not medical, legal or financial advice.
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