Muscle training on hill in California (8)
I believe the answer is:
pectoral
'muscle' is the definition.
(I know that pectoral is a type of striated muscle tissue)
'training on hill in california' is the wordplay.
'training' becomes 'PE' (Physical Education).
'on' means one lot of letters go next to another.
'hill' becomes 'tor' (tor is a kind of hill).
'in' is an insertion indicator.
'california' becomes 'cal' (short for California).
'tor' placed within 'cal' is 'ctoral'.
'pe'+'ctoral'='PECTORAL'
(Other definitions for pectoral that I've seen before include "Of the chest or breast, like muscles" , "Of the chest, say muscles" , "Alert cop about chest" , "(Large muscle) of the chest" , "Relating to the breast or chest" .)