Beat runner, for example (5)

I believe the answer is:

pulse

I'm a little stuck... Click here to teach me more about this clue!

'beat' is the definition.
(I know that beat is a is a more specific form of the action of pulse)

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for pulse that I've seen before include "A vital sign turning" , "Healthy food" , "Edible seeds - which nurse may take" , "Series of rhythmic beats" , "Heart beat - peas, beans etc" .)

I've seen this clue in The Guardian.

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