Review Question - QID 219983

The phase of throwing shown in Figure A represents early cocking, during which the deltoid (muscle D) reaches peak muscle activation (Answer 4).

There are 5 main phases of throwing (Figure A; Illustration A): wind up, cocking (divided into early and late), acceleration, deceleration, and follow-through. The entire throwing motion takes approximately 2 seconds, with the wind up and acceleration phases taking up approximately 75% of this time (1.5 seconds). In order to execute this motion, the scapula must work in concert with the humerus to maintain glenohumeral stability, while sustaining supra-physiologic forces imposed by the muscles surrounding the joint. Specifically, during early cocking, the deltoid reaches peak muscle activation, while the supraspinatus, infraspinatus, and teres minor reach peak muscle activation during late cocking. Conversely, during windup and follow-through, upper extremity muscle activation is minimal.

Escamilla et al. reviewed pitching biomechanics as a pitcher approaches muscular fatigue during a simulated baseball game. The authors had 10 collegiate baseball pitchers throw 15 pitches per inning for 7 to 9 innings off an indoor throwing mound during a simulated baseball game, recording with a 6-camera 3D automatic digitizing system, and found that compared with the initial 2 innings, as a pitcher approached muscular fatigue during the final 2 innings he was able to pitch, there was a significant decrease in ball velocity, and the trunk was significantly closer to a vertical position. They concluded that the study did not support the idea that there is an increase in shoulder and elbow forces and torques as muscular fatigue is approached.

Chalmers et al. reviewed the current concepts regarding the relationship between pitching mechanics and injury. The authors note that the overhand pitch is one of the fastest known human motions and places enormous forces and torques on the upper extremity. The pitching motion is a kinetic chain, in which the force generated by the large muscles of the lower extremity and trunk during the wind-up and stride phases are transferred to the ball through the shoulder and elbow during the cocking and acceleration phases. They conclude that altered knee flexion at ball release, early trunk rotation, loss of shoulder rotational range of motion, increased elbow flexion at ball release, high pitch velocity, and increased pitcher fatigue may increase shoulder and elbow torques and risk for injury.

Figure A represents the phases of throwing with the early cocking phase highlighted with the arrow. Figure B is a sagittal MRI sequence showing the following labeled shoulder muscles: (A) subscapularis (B) supraspinatus (C) teres minor (D) deltoid (E) conjoint muscles (short head of biceps brachii and coracobrachialis). Illustration A is a labeled figure depicting the phases of throwing.

Incorrect Answers:
Answers 1: The subscapularis is most active during the late-cocking and early acceleration phases of throwing.
Answers 2 and 3: The supraspinatus and teres minor achieve peak activation during late cocking.
Answer 5: The contribution of muscular activation of the short head of the biceps brachii and coracobrachialis is minimal during the throwing motion.