Healthier machinist (6)
I believe the answer is:
fitter
This clue is a double definition.
'healthier' is the first definition.
('fit' is associated in meaning with 'healthy')
'machinist' is the second definition.
(I know that machinist can be written as fitter)
(Other definitions for fitter that I've seen before include "less likely to feel fatigue" , "Workman" , "A skilled technician" , "Mechanic" , "Assembler; more suitable" .)