Understanding Arm Anatomy and Function

The arm consists of the long humerus bone and the forearm bones, the radius and the ulna. The connection between the humerus and forearm bones forms the elbow joint. The metacarpal bones form the wrist, the carpals form the hand, and the phalanges form the fingers and thumbs. Important bony projections on the humerus serve as locations for muscle and ligament attachments and can also be the sites for injury. When the arm is in the anatomical position (palms up), the medial epicondyle is the rounded part of the bone on the inside of the elbow and the lateral epicondyle is the one on the outside. These two sites are attachment points for the medial and lateral collateral ligaments that hold the humerus to the radius and ulna. They are also the points where many wrist and finger flexor and extensor muscles originate. Since many of these muscles attach at the same site, their tendons (which attach muscle to bone) are often referred to in groups: the common extensor tendons (CET) and the common flexor tendons (CFT).

The muscles of the arm can bend (flex) and extend (straighten) the elbow and supinate (rotate the palm up), and pronate (rotate the palm down) the forearm; they can also flex, extend, abduct (bring the body part away from the midline of the body) and adduct (bring the body part toward the midline of the body) the wrist and fingers. The thumb and little finger have their own movement, called opposition, which allows us to hold on to objects. The muscles in the hand are highly specialized and coordinated. Although they are small, they pack a wallop. They can do intricate movements such as playing the piano or typing, and they can perform gross motor movements such as hanging on to a pulldown bar or holding a bag of groceries. Figure 10.1 shows the many muscles and bones of the arm. Table 10.1 describes the functions of these muscles.

Some say that two heads are better than one. If that is true, then three heads will surely crush the competition. In Latin, biceps means two heads and triceps means three heads. The biceps muscle has two tendons that attach in different places and also two different muscle bellies or heads that arise from these tendons, but these two muscles join together to share a common tendon insertion on the forearm. The same is true for the triceps, except that it originates from three tendons and has three different heads that join together for a common tendon insertion on the elbow. This anatomy is nice to know, but how does it affect your training? It should have an impact on the variety of exercises you do. Because of the different origins of the heads, you need to train these muscles using different exercises and angles to emphasize each head.

Figure 10.1 Muscles and bones of the arm and hand.

The tendon of the short head of the biceps muscle attaches on the coracoid process of the scapula and assists with both flexion of the humerus at the shoulder joint and flexion of the elbow. The long head of the biceps tendon travels through the bicipital groove of the humerus and attaches to the top of the scapula at the shoulder joint, but has no action at that joint. It just flexes the elbow and supinates the forearm. Therefore, to work both biceps heads you must not only do elbow flexion and forearm supination exercises (like a standard biceps curl), but also add some humerus flexion to the mix. Usually when we do biceps curls we get in a little bit of humerus flexion anyway. You can add a little extra arm flexion to work on the short head by moving your humerus up slightly as you flex your elbows. So instead of aiming for your chest, you are aiming for your eyes. Realize that any humerus flexion movement you do will involve the biceps short head as well.

All three triceps heads extend the elbow, but the long head that attaches to the bottom of the scapula also helps to extend the humerus. It receives more stress when you bring your arm slightly backward during an exercise, as when you do a one-arm cable pushdown with a reverse grip, in which you get some shoulder extension with the elbow extension. The lateral head of the triceps attaches on the back of the humerus and seems to work hard no matter what elbow extension exercise that you do.

The medial head is buried beneath the lateral head and is equally accentuated during many elbow extension exercises. Of these exercises, the overhead cable extension exercises tax all three heads the most. They involve full shoulder flexion and may stress the triceps more because you put the muscle on stretch and then force it to perform a contraction.

The bottom line is to vary your exercises from all angles so that you've sure to get the arms you'll be proud to show off in a tank top. The exercises in this chapter, with the many variations offered, will help you reach this goal.

TRAINING AROUND TENNIS ELBOW