After short time, added piece that can give more power to your elbow (7)
I believe the answer is:
triceps
'can give more power to your elbow' is the definition.
I can't tell whether this definition defines the answer.
'after short time added piece' is the wordplay.
'after' is a charade indicator (letters next to each other).
'short time' becomes 'trice' (a short time, eg in phrases like 'in a trice').
'added piece' becomes 'PS' (as in a postscript to a letter).
'trice' put next to 'ps' is 'TRICEPS'.
'that' acts as a link.
Can you help me to learn more?
(Other definitions for triceps that I've seen before include "one can't bend the elbow!" , "Source of uplifting strength" , "Extensor muscle" , "Muscle that extends the forearm" , "Three-headed muscle" .)