Review Question - QID 219983

A 17-year-old high school baseball pitcher presents to the clinic with the complaint of vague shoulder pain in his throwing arm. He has been abiding by proper pitch counts during the season, but has been augmenting his off-season training regimen in preparation for his collegiate career. As a sports medicine-trained physician, you explain to him the supra-physiologic forces sustained on the shoulder during the throwing motion. Which of the following labeled muscles in Figure B experiences peak muscle activation during the phase of throwing demarcated in Figure A?