<prompt> Overhead abduction at shoulder joint is caused by which muscle -DeltoidSupraspinatusSerratus anteriorPectoralis major  <response>: 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. 