Drive, having one medium exercise left (5)
I believe the answer is:
impel
'drive' is the definition.
(I know that drive is a more specific form of the action impel)
'one medium exercise left' is the wordplay.
'one' becomes 'i' (Roman numeral).
'medium' becomes 'm' (as in UK clothing sizes).
'exercise' becomes 'pe' (Physical Education).
'left' becomes 'l' (common abbreviation).
'i'+'m'+'pe'+'l'='IMPEL'
'having' is the link.
(Other definitions for impel that I've seen before include "Make" , "Press on - drive forward" , "Force forwards" , "Urge or drive to do something" , "Hold together" .)