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Many professional researchers are still looking for an answer. Damage to the tendon attaching the extensor carpi radialis brevis (ECRB) muscle to the elbow is the cause of the pain, but the cause of this cause is a mystery. However, it is fairly certain that this type of damage is the result of repetitive stresses, such as hitting a tennis ball. Producing causes of tennis elbow may include the following mechanisms, which are offered here for comment and further investigation:
(1) Elbow Crunch is a sudden shortening of the ECRB due to impact (explained at greater length above under Elbow Crunch). This effectively is a muscle spasm that stresses the tendons. (2) On impact, the resultant Torque twists the racquet head back, while Moment is dragging the head down, and the hand is holding the racquet steady. The resultant twist of the handle (Torsion, or Longitudinal Torque) is clockwise for a right-handed forehand. This twist winds up a catapult. When the ball leaves the racquet, the catapulting force is counterclockwise for the right-handed forehand. The two opposite screwdriver twists in a short time give a severe stress cycle to the extensor carpi radialis brevis muscle that attaches the middle of the hand to the elbow, even for a dead-center hit. (3) The back-and-forth catapulting stress cycle of Torque from impact twisting the racquet back, followed by catapulting the racquet forward when the ball leaves, aggravates the handle twist cycle mechanism discussed above under (2). The extensor carpi radialis brevis muscle is anchored at the elbow and at the metacarpal (hand) bone of the middle finger, on the index finger side. The resultant Torque from impact is a twist backward that tends to yank this muscle as the middle finder is extended. On impact, this muscle is either straining (on the backhand) or slack (on the forehand). On the backhand, the first twist yanks this straining muscle, further stressing the tissues attaching it to the elbow. Then the muscle suddenly loses resistance but continues to work against the combined stress, so it suddenly shortens after impact, giving an even more severe yank to the elbow (cf. the discussion below on Elbow Crunch). For the forehand, the muscle is slack on impact, so the catapulting stress cycle cracks the muscle like a whip, stressing the points of attachment at the wrist and elbow. Elbow straps help because they damp the whip effect. (4) Shock becomes internal energy, which expresses itself as frame vibration, and this vibration is transmitted to the arm holding on to the racquet unless it is damped somehow. (The correct term is damped, not "dampened.") In the old wood racquets, vibration disappeared quickly because it was damped by the flex of the wood, but the new stiffer and lighter frames do a poor job of damping, so they efficiently transfer the subtle shaking to the arm. Undamped high frequency frame vibration can stealthily sabotage the elbow, so the price of power may be pain. Vibration of the frame shakes the extensor carpi radialis brevis muscle that attaches the middle of the hand to the elbow. This causes cyclic stressing of the tendons at the lateral epicondyle, where the fat half of this long teardrop-shaped muscle attaches. Cyclic stressing is how you break a coathanger by bending it back and forth. Eventually, with enough stress cycles, fatigue can cause tissues to snap, even without any tremendous force. What you don't want if you are concerned about the risk of tennis elbow is a stiff, high-Torque, high-Moment, high-Shock racquet. That means a light, head-heavy racquet. Poor stroking technique is frequently accused, conveniently diverting scrutiny from racquet design, but, as the calculations on this site prove, risk factors for tennis elbow include: (1) light racquet weight and (2) head-heavy balance. Stiff frames are also bad. What is good for minimizing elbow damage is low Shock, low Elbow Crunch, low Torque, and low Moment.
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