Last couples from drunken summer orgy get up and go (6)

I believe the answer is:

energy

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'go' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for energy that I've seen before include "Power - drive" , "'Vigour, vitality (6)'" , "Go, zip" , "Healthy capacity for vigorous activity" , "Dynamism" .)

I've seen this clue in The Independent.

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