Worker in better physical shape (6)
I believe the answer is:
fitter
I believe this is a double definition.
'worker' is the first definition.
(someone who fits things)
'in better physical shape' is the second definition.
(more physically fit)
(Other definitions for fitter that I've seen before include "Worker assembling machinery - more healthy" , "better equipped" , "to get in better shape" , "A skilled technician" , "Healthier" .)