 As the biceps originate on the scapula unlike the other two which originate on the humerus, the biceps are inclined to serve a role as a dynamic stabilizer, much as the hamstrings would during a squat.This is because, while the biceps shortens as the elbow flexes, it will also lengthen as the shoulder extends.A supinated grip at the forearm allows the biceps to contribute more strongly as an elbow flexor.