I Pinched A Nerve In My Shoulder 8 Months Ago.

I pinched a nerve in my shoulder 8 months ago. Finally got back into gym but lots of weakness in left tricep and shoulder area. Muscle develope , size and tone in left side noticably deminished. Currently doing isolation movements to improve strenth. What muscle work in tandem with triceps that would need attention to return strenth in this area?