Carry out most of device for training muscles (8)
I believe the answer is:
exercise
'carry out' is the definition.
(synonyms)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for exercise that I've seen before include "written school task" , "Do it to develop skill or fitness" , "Task set to practise" , "Use" , "Practice task" .)