Muscle runs around ends of clavicle (7)
I believe the answer is:
triceps
'muscle' is the definition.
(I know that triceps is a muscle)
'runs around ends of clavicle' is the wordplay.
'runs' becomes 'trips' (I can't explain this - if you can you should give a lot more credence to this answer).
'around' is an insertion indicator.
'ends of' says to hollow out the word (remove centre letters).
'clavicle' with its middle taken out is 'ce'.
'trips' going around 'ce' is 'TRICEPS'.
Can you help me to learn more?
(Other definitions for triceps that I've seen before include "army feature?" , "Muscle that extends the forearm" , "one can't bend the elbow!" , "Three-headed muscle" , "Muscles" .)