Green’s Dictionary of Slang

fitness n.

[fit adj. (2)]

(UK black) attractiveness; an attractive (young) woman.

[UK]C. Newland Scholar 175: Buy somet’ing to help yuh mek up wi’ dat fitness y’ave, some jewellery or sumt’in’.
[UK](con. 1979–80) A. Wheatle Brixton Rock (2004) 86: I wanna chat to that masterpiece of fitness called Verna.
[UK]G. Malkani Londonstani (2007) 19: If yous lot wanna see proper fitness you shoulda seen dis bitch I shagged last weekend.