Biceps Brachii

The long head of the biceps originates from the supraglenoid tubercle of the scapula and runs along the bicipital groove of the humerus. It's the outer portion of the biceps, the one that forms the 'peak'. The short head originates from the coracoid process of the scapula and is the inner portion. Both heads merge into a common tendon that inserts on the radius. The biceps crosses both the shoulder and the elbow, which means arm position influences its recruitment.

The biceps works most when you flex the elbow with the palm facing up (supination). The supinated dumbbell curl is the exercise that activates it maximally. With a neutral grip (hammer curl) or pronated grip (reverse curl), the biceps works less and the brachialis and brachioradialis take over. The long head stretches more when the arm is behind the body: incline bench curls put it in maximum stretch and produce more hypertrophic stimulus.

Developing complete biceps requires working both heads. Incline bench curls emphasize the long head. Preacher curls or spider curls emphasize the short head because the arm is in front of the body. The classic standing barbell curl is a great general exercise. You don't need twenty variations: two curl movements at different angles with consistent progression are all you need.