The Physiological Basis for
Conditioning Baseball and
Softball Players, Part 2: Training the Arm - 7/26/06
Some continue to argue that strength and conditioning for ball players, and baseball pitchers in particular, is unnecessary and time wasting.
Proponents of this thinking remind me of soldiers that were found, isolated, on islands in the Pacific after the conclusion of World War II. Operating on limited information, they were still prepared and willing to fight a war that everyone else knew was over. The thinking of these soldiers was erroneous because they didn't have access to accurate, up to date information to inform their decisions.
closely at these pictures:
A couple of questions:
1) Do these mechanically correct arm actions look particularly "natural" or healthy? (They look kind of freakish to me.)
2) You think this is stressful only on the muscles and tendons involved? In fact, the pitching maneuver subjects the humerus (upper arm) bone to torsional loads considerably greater than that required to actually fracture the bone! 
The functional arc of elevation of the shoulder is forward, not lateral.  Yet much of the functional arc of the act of pitching is lateral, as the above pictures clearly illustrate.
When the arm assumes a position of humeral external rotation combined with horizontal abduction, it is placed in a compromised position known as the "at risk" position. 
This is very similar to the position the arm is in at ball release during a pitch or throw.
When the arm is in this position, whether from throwing, weight lifting, or other activities, shoulder laxity, instability, or impingement can result. All of these can lead to arm injuries for pitchers (or any overhand thrower). [4, 5]
One thing baseball pitchers can do to reduce the risk of developing impingement is to fully externally rotate the shoulder when the arm is in what is commonly called the "high cock" position. The mechanics of my old college teammate and MLB pitching great, Jack Morris, were a good example of this.
Another key thing is to modify certain weight lifting exercises so as to keep the arm from assuming this position.
Hence, even the best pitching mechanics impose stresses that are potentially damaging to the elbow and shoulder.
And what of the pitcher with poor mechanics?
Proper strength and conditioning is even more critical for these players. To be successful, pitchers must work on more than just mechanics!
Can anyone possibly doubt that pitching mechanics are physically stressful and require appropriate strength and conditioning work for the arm and body to stay healthy?
Notice the hand. This is the normal arm/hand position after ball release - pronation. It is defined as the rotation of the arm so that the hand moves from a palm-up to a palm-down position.
Keep in mind that the arm pronates regardless of the pitch thrown, including curves and sliders. This has important implications as to how the arm should be conditioned, and it is easy to see how curves and sliders can damage an arm, especially in younger pitchers.
When a ball is thrown, the upper arm itself is also being "thrown." Various tissues keep it from actually detaching, of course, but the most injurious part of the pitching delivery (assuming good mechanics) is commonly referred to as the deceleration phase. This phase occurs upon ball release and the follow-through in both baseball and fastpitch softball pitchers.
Muscles do two things: contract and relax. They do not flex - flexion is a joint action, not a muscle action. There are three types of muscle contractions - concentric, eccentric, and isometric.
Concentric contractions occur when a muscle is actively shortening, as in the upward phase of an arm curl. Eccentric contractions occur when a muscle is actively lengthening, as in the downward phase of an arm curl. Isometric contractions produce no lengthening or shortening; the muscle is in a static state. There is no movement, as in the position of the arm during a biceps curl with the arm in a fully extended, or down position.
Greater muscle fiber damage and soreness are associated with eccentric contractions than either concentric or isometric. There are a number of muscles that contribute to pitching and throwing. We'll focus here on the decelerators.
There are three arm decelerator muscles:
These muscles perform their work after a pitch or throw by contracting "eccentrically." They bear the brunt of the force generated by the rest of the body that results in a high velocity throw. The rather abrupt ending to the throwing process occurs by way of these small, actively contracting muscles.
So, these and other arm muscles are clearly very active during the act of throwing or pitching. The arm is doing more than just being passively whipped along for the ride generated by the momentum of the lower body.
Arm deceleration forces have been estimated to be twice that of acceleration forces while acting over a period of time that is twice as long. It has further been reported that during isotonic exercise (muscle shortening while working under a constant load), the eccentric force of a muscle increases as the velocity of movement increases.
This is precisely what the throwing arm is doing. The decelerator muscles are performing an isotonic exercise (throwing) under a constant load (a 5 oz baseball) up to ball release, and the muscles are contracting concentrically to facilitate arm acceleration. After ball release, these muscles then contract eccentrically to decelerate the arm.
As you might guess, all of this has important implications for the kinds of strength and conditioning work required to keep a ball player's arm healthy. We'll discuss this further in a future issue of LINE DRIVES.
 Yamada, H. and Evans, F. Strength of Biological Materials, Baltimore: Williams and Wilkins, 1972, pp. 69-70.
 Neer, C.S. Anterior Acromioplasty for the Chronic Impingement Syndrome in the Shoulder. Journal of Bone Joint Surg. 54A: 41-50, 1972.
 Gross, M.L., S. L. Brenner, I. Esformes, and J.J. Sonzogni, "Anterior Shoulder Instability in Weight Lifters." American Journal of Sports Medicine 21.4 (1993): 599-603
 O'Connell, P.W., G.W. Nuber, R.A. Mileski, and E. Lautenschlegaer. The contribution of the genohumeral ligaments to anterior stability of the shoulder joint. American Journal Sports Medicine 18(6): 579-584, 1993
 Kamkar, A., J.J. Irrgang, and S.L. Whitley. Non-operative management of secondary shoulder impingement syndrome. Journal Orthop. Sports Phys. Ther. 17(5):212-224. 1993
 Jobe, F. W., Radovich Moynes, D. Tibone, J.E. and J. Perry, 1984. An EMG analysis of the Shoulder in Pitching. A Second Report. American Journal of Sports Medicine 12(3): 218-220.
 Komi, P.V. 1973. Measurement of the Force-Velocity Relationship in Human Muscle under Concentric and Eccentric Contractions. Med, and Sport: Biomechanics III. 8:224-229
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