This movement is the combination of the radial deviation described above, and the corresponding countermove, called ulnar deviation. To understand ulnar deviation, extend you arm the top of your hand in line with the forehand. Now simply flex your wrist to the right without breaking it forward. That’s ulnar deviation.
Ulnar deviation is usually greater than radial deviation. In a neutral position the wrist would be straight and in line with the forearm. However, when playing table tennis the wrist would usually stay in an ulnar flexed position throughout the rally (as we want our bat, instead of our hand, to be in line with our forearm).
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Overloading of the wrist joint in extension and ulnar deviation, which can occur when executing forehand strokes during tennis playing or with weight training, could represent factors contributing to the development of these bone stress injuries, for which conservative treatment is recommended.
Often, the pain presents on the pinkie-side, or ulnar side, of the wrist. Many players experience this ulnar pain in the non-dominant hand during two-handed backhand strokes. In this stroke, the top hand is placed in extreme ulnar deviation and extension, while dynamically moving from supination to pronation.
In the video you mention turning a door knob at contact (supination), but it looks like you may be moving from ulnar deviation to radial deviation. Two questions: can you confirm for me which of these motions you use while hitting the forehand and 2) whether it is a conscious muscular effort or simply the result of racket momentum and a loose arm?
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In tennis, wrist injuries most commonly occur during forehand groundstrokes. This is the most commonly used stroke and is performed with the dominant forearm in full supination (outward roll) and the wrist flexed in ulnar deviation (fingers bending toward the ulna bone away from the thumb).
Turn sideways, place your racket into its starting position for your forehand, and then lightly rotate your trunk and swing forward. Start at half speed and work up from there. Relax your hand, and swing out, up, and through an imaginary ball in front of you. Observe your string angle through the hitting zone.
Subluxation of the ECU tendon, although not truly an overuse syndrome, is an important differential diagnosis in the tennis player with ulnar wrist pain. Subluxation of the ECU results from rupture or attenuation of the ECU subsheath caused by a sudden volar flexion and ulnar deviation stress, such as hitting a low forehand 38 . Diagnosis can be made by having the athlete actively ulnarly deviate the wrist in full supination, observing the ECU tendon subluxating ulnarward over the styloid.