Back muscles hampering mum's dance (5)
I believe the answer is:
samba
'dance' is the definition.
(Brazilian dance)
'back muscles hampering mum's' is the wordplay.
'back' says the letters should be written backwards.
'muscles' becomes 'abs' (I've seen this before).
'hampering' indicates putting letters inside (hamper can mean to obstruct or restrain).
'mum' becomes 'ma' (ma can mean mother).
'abs' placed around 'ma' is 'abmas'.
'abmas' backwards is 'SAMBA'.
(Other definitions for samba that I've seen before include "This ambassador's > brisk steps" , "Latin dance" , "Brazilian dance" , "South American dance" , "Dance music" .)