Overhead abduction at shoulder joint is caused by which muscle -
Ans. is 'c' i.e., Serratus anterior o Abduction is initiated by supraspinatus, which is responsible abduction upto 15deg. After that deltoid (acromial or middle fibers) is the major abductor upto 90deg of abduction. These two muscles, supraspinatus and deltoid are the prime movers for abduction. Overhead abduction (> 90deg) is caused by trapezius and serratus anterior, which act by causing upward rotation of glenoid cavity.
Deltoid
Supraspinatus
Serratus anterior
Pectoralis major