 Sal Cinquemani from Slant Magazine characterized " Fighter " as a hybrid of R & B and rock . Meanwhile , a reviewer of Billboard described the song as arena rock @-@ influenced , and AOL Music 's Nana @-@ Adwoa Ofori noted the elements of rock and roll . However , Nick Levin from Digital Spy detailed " Fighter " as an arena rock piece . The song was inspired by band Guns N ' Roses ' song " November Rain " ( 1992 ) . Written in the key of E minor , " Fighter " has a moderate tempo of 96 beats per minute . Brian Hiatt from Entertainment Weekly and Chuck Taylor for Billboard likened the track 's musical style to that of Janet Jackson 's " Black Cat " . Aguilera 's vocals on the track span from the low @-@ note of G2 to the high @-@ note of F ♯ 5 ; Taylor labelled Aguilera 's vocals " tornado of a vocal . " 
