Arm Acceleration

The arm-acceleration phase is the short time from maximum shoulder external rotation to ball release (Fig. 2.1H,I). The entire phase lasts only a few hundredths of a second. A maximum elbow angular velocity of 2100° to 2700° per second occurs approximately halfway through the acceleration phase.24 Maximum elbow angular velocity is similar for the fastball, curveball, and slider pitches, but is markedly less during the change-up pitch (Table 2.2).35 This rapid elbow extension may be due primarily to centrifugal force acting on the forearm because of the rotating trunk and arm; the elbow extensors are unlikely to shorten fast enough to generate the high angular velocity measured at the elbow.

Several studies have examined the role of the triceps in extending the elbow during the acceleration phase of throwing.24,26,28,34,36 Roberts reported that a pitcher with a paralyzed triceps due to a differential nerve block was able to throw a ball at more than 80% of the speed attained before paralyzation.34 This finding seems to support the concept that the triceps contraction does not generate most of the elbow extension velocity and that centrifugal force is a major factor. Electromyography has shown high triceps and anconeus activity during the arm-acceleration phase, suggesting that the triceps initiates or contributes to some of the angular velocity generated during this phase.24,26,28,36 However, these muscles may function more as elbow stabilizers than as accelerators.25

Toyoshima et al. compared normal throwing using the entire body with throwing using only the forearm to extend the elbow.37 The latter forearm throw involved a maximum voluntary effort to extend the elbow with the upper arm immobilized. Assuming that the triceps muscle shortened as fast as voluntarily possible during the forearm throw, the resulting elbow angular velocity is the maximum that could be generated with maximum triceps contraction alone. The results from this study showed that normal throwing generated approximately twice the elbow angular velocity that could be achieved during the forearm throw. The authors concluded that the elbow was swung open like a whip and that the elbow angular velocity that occurs during throwing is due more to the rotary actions of other parts of the body (e.g., hips, trunk, and shoulder) than to the elbow-extending capabilities of the triceps. They also showed that forearm throwing produced only 43% of the ball velocity generated in normal throwing.

Ahn used computer simulations and optimization techniques in comparing theoretical data with experimental data.38 The data showed that hand velocity at ball release was approximately 80% of the experimental value when the resultant elbow joint torque was set to zero, approximately 95% of the experimental value when the resultant wrist joint torque was set to zero, and approximately 75% of the experimental value when both the resultant elbow and wrist joint torques were set to zero. Consequently, he concluded that body segments other than the upper extremity (i.e., lower extremities, hips, and trunk) primarily generated ball velocity at release.

During arm acceleration, the need to resist valgus stress at the elbow can result in a wedging of the olecra-non against the medial aspect of the trochlear groove and

FIGURE 2.5. Time-matched measurements during the baseball pitch: (A) elbow flexion, (B) force applied at the elbow, (C) torque applied at the elbow, and (D) electromyographic muscle activity. (Adapted from Werner et al.24)

the "valgus extension overload" mechanism that Wilson et al. described.23 Campbell et al. found greater valgus torque (normalized by body weight times height) in 10-year-old pitchers than in professional pitchers at the instant of ball release. They believed this finding might be related to Little League elbow syndrome in young pitchers.39

As the elbow extends and the upper torso continues to rotate, a maximum elbow compressive force of 800 to 1000 N is produced at ball release to prevent elbow distraction due to the centrifugal force acting on the forearm (Fig. 2.4).20 In addition, low to moderate activity from the elbow flexors generates a maximum elbow flexor torque of 40 to 60 N-m (Fig. 2.2).20,26,28 Contraction of the elbow flexors in this phase adds compressive force for joint stability and also controls the rate of elbow extension.

Cure Tennis Elbow Without Surgery

Cure Tennis Elbow Without Surgery

Everything you wanted to know about. How To Cure Tennis Elbow. Are you an athlete who suffers from tennis elbow? Contrary to popular opinion, most people who suffer from tennis elbow do not even play tennis. They get this condition, which is a torn tendon in the elbow, from the strain of using the same motions with the arm, repeatedly. If you have tennis elbow, you understand how the pain can disrupt your day.

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