On spring break you travel to Malibu, California. While there, you visit the famous Malibu beach to observe the parade of body builders. They each show off their massive muscles with the standard "pump you up" arm flexion. Which muscle would be least involved with this action?

Supraspinatus.

Explanation:

Supraspinatus is the small muscle that lies that lies on the upper back region of the body. This muscle runs to the superior portion of the scapula into the humerus through the greater tubercle.

The supraspinatus muscles are mainly involved in the arm aduction and pulling of the head of the humerus. The builders shoe arm flexion. The biceps brachii muscle is involved in the arm flexion. The least that involved in the arm flexion is supraspinatus muscle.

Thus, the answer is supraspinatus.