Basic Upper Extremity Rotations - (excluding elbow flexion and extension)

The upper extremities have a pretty amazing repertoire of positions, largely because of the impressive range of motion of the shoulder and wrist. The following are the motions that we will be using to 'construct' tennis strokes:

Shoulder:

• Rotation - internal <> external
• Horizontal Flexion - forward <> back
• Vertical Flexion - up (abduction) <> down (adduction)

Elbow:

• Flexion - flexion <> extension
• Rotation - pronation <> supination

Wrist:

• Flexion - ulnar (towards the pinky finger) <> radial (toward the thumb)
• Flexion - dorsal (towards the back of the hand) <> palmar (towards the palm)

Counter Rotation of the Forearm - Internal rotation of the shoulder (hot pink arrow) and supination of the elbow (azure arrow) results in locking and loading of the arm in the forehand volley.

When a joint is rotated to the end of its range of motion it turns into a spring. The tendons and ligaments around the joint are pulled tight, and the opposing muscles are at full stretch and therefore are at maximum potential energy; the joint is 'loaded' with energy that can be released through the racquet into the ball.
The joint is also 'locked' so your body knows exactly what position it is in. Conversely when the joints of a limb are not locked, there are so many possible positions for the limb that it is a wonder we aren't constantly punching ourselves in the the head. A joint that is unlocked at a critical moment of a stroke has too many degrees of freedom, making the stroke erratic.

Counter-rotation is a technique that allows you to lock and load a joint would otherwise be flopping around during a stroke absorbing power, breaking the 'kinetic chain' and reducing consistency by increasing the degrees of freedom of that limb. The classic example is internally rotating the shoulder while fully splinting the forearm when hitting the forehand with the continental grip. This locks a major section of the arm at the moment of contact with the ball, keeping the racquet face from opening or closing. The tension in the ligaments, tendons and muscles also load the forearm so that it can more powerfully pronate through the stroke.