Sinewy person in front (6)

I believe the answer is:

leader

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'sinewy person' is the definition.
'leader' can be an answer for 'person' (leader is a kind of person). I am not certain of the 'sinewy' bit.

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for leader that I've seen before include "Principal first violinist" , "Front-runner or head of group" , "Head, guide" , "Pioneer" , "important member of orchestra" .)

I've seen this clue in the Evening Standard.

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