You can do chin ups in a variety of ways, all of which target the muscles of the back and arms. The chin up is performed by placing both hands on a stationary bar with arms fully extended and pulling the body up until the chin is over the bar. This is a slow and controlled movement, and the body should be kept as rigid and upright as possible throughout the exercise. The three joint actions involved in this movement are flexion of the elbow, extension and adduction of the shoulder joint and adduction and downward rotation of the shoulder girdle.
The Elbow Joint
Flexion of the elbow involves three main muscles: the biceps brachii, brachialis and brachioradialis. The extent to which each muscle is used changes, depending on the width and style of grip. For example, with an underhand grip--palms facing towards your body--the biceps brachii become much more active in flexing the elbow than they would in an overhand grip.
The Shoulder Joint
The main muscles that extend the shoulder are the latissimus dorsi, teres major, posterior deltoid, pectoralis major and the long head of the triceps brachii. Shoulder adduction is performed with the same muscles, with the addition of the subscapularis muscle. The primary movers of the shoulder joint can change, depending on the width of the hands during the chin up. If the hands are kept closer together, with the elbows in, the chin up will involve more shoulder extension and less adduction. Conversely, with a wide grip, the shoulder will be adducting more and the emphasis will be mostly on the latissimus dorsi.
The Shoulder Girdle
The shoulder girdle is adducted and downwardly rotated during a chin up. This means that the scapula is being pulled towards the center of the body and rotating in a clockwise direction. The muscles used in this action are the trapezius (lower and middle), pectoralis minor and the rhomboids.
References
- "Strength Training Anatomy"; Frederic Delavier; 2001
- "Manual of Structural Kinesiology"; R.T. Floyd; 2007
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