Kinesiology of Exercise


Athletes and bodybuilders typically do wrist curls and reverse curls in the belief that they work all the muscles of the forearm maximally, but, in fact, this is not so. Ulna and radial flexion exercises use mostly the same muscles but in their other major action. Because of this, for full development of the forearm and to more closely duplicate the exact action used in many hitting activities, you should do ulna and radial flexion.

Major Muscles and Actions Involved

In ulna flexion (hand adduction) the flexor carpi ulnaris and the extensor carpi ulnaris muscles are involved. In this action the little finger side of the hand moves toward the forearm. In radial flexion (hand abduction), the flexor carpi radialis and the extensor carpi radialis longus and brevis are involved. In this action the thumb side of the hand moves toward the forearm.

Sports Uses

Ulna flexion is the key action in the wrist break in baseball and softball batting, the golf swing, the slice tennis serve, and fly casting. It is a key action in Frisbee throwing and is used in the racquet sports when you try to impart spin to the ball (bird) in the forehand and backhand strokes. In baseball pitching it is used when throwing sinking balls, and in softball pitching it is needed for imparting side spin to the ball. Radial flexion and the muscles involved are not very important in most sports. However, they are most important in the wrist action in the discus throw and Frisbee throws.

Exercise Analysis

  • It is important to do these exercises correctly for maximum benefits. The key points are keeping your arm straight, using only your wrist, and raising the weight as high as possible (close to elbow-high in ulna flexion and slightly above the wrist in radial flexion). In radial flexion, avoid a tendency for the biceps to come into play to raise the weight higher. 
  • Ulna flexion is a classic example of muscle synergy, that is, when muscles work together to allow a specific action to occur. The flexor carpi ulnaris is involved not only in ulna flexion, but in wrist and elbow joint flexion as well. 
  • The extensor carpi radialis, which is involved in ulna flexion, is also involved in wrist and elbow joint extension. Thus, when ulna flexion takes place, the wrist and elbow joint actions neutralize each other and only ulna flexion takes place. 
  • In this exercise the flexor carpi radialis is involved in radial flexion as well as wrist flexion. The extensor carpi radialis longus and brevis are involved not only in radial flexion, but also in wrist extension. Thus, when radial flexion takes place, the wrist actions (which are opposite one another) neutralize each other's effect and only radial flexion takes place. 
  • The length of the bar that is used plays an important role in regard to resistance and range of motion. From the practical experiences of bodybuilders and athletes, I have found that the Strength Bar is best. 
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