Jan 29, 2015
Arm Forces

To keep pitchers healthy and on top of their game, you must prepare specific muscles in the arm and shoulder for tremendous rotational force and repetitive stress.

By Leonard Macrina & Dr. Michael Reinold

Leonard Macrina, MSPT, CSCS, SCS, is a Physical Therapist at Champion Sports Medicine in Birmingham, Ala. Michael Reinold, PT, DPT, ATC, CSCS, is the Rehabilitation Coordinator and Assistant Athletic Trainer for the Boston Red Sox and the Coordinator of Rehabilitation Research & Education in the Department of Orthopedic Surgery at Massachusetts General Hospital.

In baseball, pitching prowess is about consistency and repetition. Pitchers’ success in games, practices, and bullpen sessions depends on their ability to produce the same overhead throwing motion many times in close succession. Other players on the diamond need to be able to repeat an efficient throwing motion, but no one subjects his arm and shoulder to as much stress and force as a pitcher.

The repetition necessary for developing technique, accuracy, and power also creates a host of orthopedic concerns. The overhead throwing motion can lead to specific patterns of injury to the shoulder joint, and anyone who has worked with a baseball team is familiar with the most common end products–rotator cuff tears, labral tears, and strained muscles.

The good news is that we know more today than ever before about how the shoulder operates and what we can do through training to improve function and reduce injury risk. A smart conditioning approach must address key muscle groups with appropriate exercises, which can be a major challenge, since it involves familiarizing yourself with a large and ever-growing body of research. In this article, we’ll discuss some recent findings and explain what they tell us about the mechanics of throwing, the causes of injury, and how to train more effective, healthier pitchers.


Let’s start with a simple fact: Effective pitching requires considerable glenohumeral joint (shoulder) mobility. One study that examined the total range of motion (ROM) of 372 pro baseball players found an average external rotation (ER) of 129 degrees and an average internal rotation (IR) of 61 degrees in the throwing shoulder at 90 degrees of abduction. In plain terms, that means elite players must have incredible flexibility in their throwing shoulder, supported by strong musculature and healthy, resilient ligaments and tendons.

If you’ve ever worked with pitchers, this comes as no surprise. But a deeper look at the stresses created by the throwing motion reveals some less intuitive and more useful information.

In our own recently published research, we examined players’ shoulder range of motion before and immediately after baseball pitching and noted a statistically significant decrease (9.5 degrees) in IR passive ROM after pitching. We hypothesized that this decrease was caused by the great eccentric forces placed on the external rotator muscles during the follow-through phase, which suggests that IR passive ROM must be addressed during training to lower a pitcher’s risk of injury.

Other researchers have looked at the forces generated in both the shoulder and the elbow during the pitching motion and found both to be incredibly high. One study found angular velocity–a measure of rotational speed–at the shoulder joint to be greater than 7,000 degrees per second. During follow through, the elbow extended at 2,300 degrees per second, producing a medial shear force of 300 Newtons and a lateral compressive force of 900 Newtons.

These figures essentially show that the arm and shoulder complex are under great stress during the act of pitching, and the risk of injury from even minor strength imbalances, intrinsic or extrinsic weaknesses, or improper mechanics is high. And remember that movement integrity isn’t a static concept–throwers with great mechanics and a solid strength base can still put themselves at risk when muscle fatigue sets in, especially if it leads to movement compensations.


An exercise program for pitchers should improve flexibility, dynamic stability, and strength while enhancing explosive power and endurance. You must provide careful supervision so the athlete maintains ROM but does not employ excessive motion. Strengthening exercises should improve muscle strength and endurance while avoiding possible side effects, such as tightness and inflexibility.

A more specific goal is developing functional stability of the glenohumeral joint. This is accomplished through the interaction of the static stabilizers (joint capsule, ligaments, and glenoid labrum) and the dynamic stabilizers (shoulder musculature), and by training the integrated functions of neuromuscular control and dynamic stabilization of the surrounding muscles, particularly the rotator cuff as it blends with the joint capsule.

Dynamic stabilization of the glenohumeral joint is achieved through interaction between several active mechanisms. The muscles primarily involved include the rotator cuff, deltoid, and biceps brachii. Secondary stabilizers include the pectoralis major, latissimus dorsi, and the scapulothoracic musculature (trapezius group, rhomboids, serratus anterior, pectoralis minor, and levator scapulae).

Recent research has shed some new light on how these muscles work in concert during the overhead throwing motion. An electromyographic (EMG) analysis of pitchers, for instance, revealed the specific muscle-firing patterns involved in a fastball delivery: During the wind-up phase, there is relatively low muscle activity in the dominant arm, but during early “cocking,” the serratus anterior and trapezius actively stabilize the glenoid as the humerus is abducted to approximately 104 degrees. The supraspinatus and deltoids stabilize the humerus within the glenoid.

During late cocking, the humerus maintains its level of abduction and gains much of its dynamic stability through activation of the middle trapezius, rhomboids, and levator scapulae. The serratus is also activated, to oppose the isometric contraction of the retractor group and maintain the position of the glenoid. In addition, the infraspinatus and teres minor are highly active to externally rotate the humerus.

The upper fibers of the subscapularis also have increased activity, thus offering a compressive force for the externally rotated humerus. During the acceleration phase, the scapula stabilizers maintain relatively high activity (above 50 percent in the manual muscle test). The latissimus dorsi and upper fibers of the subscapularis are even more active (above 85 percent in the manual muscle test) as the humerus internally rotates and horizontally adducts.

During the deceleration phase, all the scapula stabilizers are highly active, especially the lower trapezius. The teres minor serves as a key posterior restraint, and possibly a force couple, to the pectoralis major, which adducts and internally rotates the humerus.

Throughout most shoulder movement, the rotator cuff is an important dynamic joint stabilizer. The surrounding structures also play a vital role by dynamically stabilizing the joint, allowing it to produce and dissipate the large forces generated during each pitch. Deficiency of these muscle groups can lead to a variety of injuries to the labrum capsule or the rotator cuff itself.


How can all this data affect the exercise prescriptions you provide to pitchers? Obviously, the answer varies depending on training goals, existing symptoms of deficiency, weakness, or movement compensation, and past or present injuries. But in general, the research suggests special emphasis should be given to the supraspinatus, infraspinatus, and teres minor, as well as the scapula stabilizer muscles. They lay the foundation upon which optimal power and sound technique are built.

As for which exercises are best, there’s some controversy about the ideal way to position, isolate, and strengthen the supraspinatus muscle, and this has led several study authors to use EMG analysis in an attempt to resolve the issue. There is no consensus yet, and one of the main points of contention involves the relative value of “empty can” and “full can” exercises.

Frank Jobe, MD, pioneer of Tommy John ligament replacement surgery, was the first to recommend empty can exercises for strengthening the supraspinatus. This involves elevation in the scapular plane (30 degrees anterior to the frontal plane) with glenohumeral IR to shoulder height only. Meanwhile, others believe in the full can position, which involves elevation in the scapular plane with glenohumeral ER to shoulder height.

We recently conducted a study of the supraspinatus and deltoid musculature using EMG during full can, empty can, and prone full can exercises. We found that all three provided a similar amount of supraspinatus activity (ranging from 62 to 67 percent of maximal voluntary isometric contraction).

However, we did observe one key difference: The full can exercises resulted in significantly less middle and posterior deltoid activity. This led us to conclude that the full can may be a superior exercise, since it is able to strengthen the supraspinatus while minimizing potentially damaging superior shear force due to deltoid activity.

The two other key muscles targeted in the overhead throwing athlete are the infraspinatus and teres minor. These comprise the posterior cuff, providing glenohumeral compression and resisting superior and anterior humeral head translation by exerting an inferoposterior force to the humeral head. The posterior cuff muscles also provide glenohumeral external rotation, and pitchers rely on them to maintain adequate glenohumeral joint congruency during each throw.

Some researchers have found that overhead throwers most often experience rotator cuff tears from the mid-supraspinatus posterior to the mid-infraspinatus area, which they surmise is a result of compressive force produced to resist distraction, horizontal adduction, and internal rotation at the shoulder during arm deceleration. Thus, the external rotators often appear weak and affected by different shoulder pathologies such as internal impingement, joint laxity, labral lesions, and rotator cuff lesions–particularly in pitchers.

To head off these potential problems, some studies suggest emphasizing ER strengthening for throwing athletes to enhance muscular strength, endurance, and dynamic stability. This is another area where the best exercises are not universally agreed upon, so we recently conducted a study analyzing EMG of the infraspinatus, teres minor, supraspinatus, posterior deltoid, and middle deltoid of 10 healthy pitchers during seven different exercises. The exercises we studied were:

• prone horizontal abduction at 100 degrees with full ER • prone ER at 90 degrees of abduction • standing ER at 90 degrees of abduction • standing ER at 45 degrees in the scapular plane • standing ER at 0 degrees of abduction • standing ER at 0 degrees of abduction with a towel roll • side-lying ER at 0 degrees of abduction.

We found the greatest infraspinatus and teres minor activation with side-lying ER, followed closely by ER in the scapular plane and prone ER at 90 degrees of abduction. We also found that adding a towel roll to the ER exercise at 0 degrees of abduction consistently resulted in greater activity of the posterior rotator cuff–by an average of 20 to 25 percent.


We’ve discussed how the supraspinatus, infraspinatus, and teres minor lay the foundation for optimal throwing. But to develop truly complete pitchers whose risk for injury is as low as possible, other specific muscles must be targeted as well.

The trapezius, for example, provides scapular upward rotation and elevation (upper trapezius), retraction (middle trapezius), and upward rotation and depression (lower trapezius). In addition, the inferomedial directed fibers of the lower trapezius may contribute to posterior tilt and external rotation of the scapula during arm elevation, which decreases subacromial impingement. For this reason, the lower trapezius is very important to pitchers, particularly during rehab from most shoulder injuries.

Analysis of EMG patterns of the lower trapezius has found that the best exercises for developing this muscle area are the prone full can, prone ER at 90 degrees, and prone horizontal abduction at 90 degrees with ER. These findings come with one important caveat: The prone full can exercises should not be performed at a preset degree of abduction, but should instead be individualized based on the alignment of the lower trapezius fibers. A good starting point is 120 degrees of abduction, and you can make appropriate adjustments based on the athlete’s feedback and performance.

We have found that muscle imbalances often lead to shoulder pain, and a common culprit is an imbalance between the lower and upper trapezius, with the upper portion usually more dominant. To address this problem, the athlete must recruit the lower trapezius. At least one study has found bilateral ER at 0 degrees of abduction to be the most effective strategy when compared with other trapezius exercises. Another study found side-lying ER and prone horizontal abduction at 90 degrees with ER to help balance lower and upper trapezius activity.

Other exercises that develop the lower trapezius include prone rowing, prone horizontal abduction at 90 degrees and 135 degrees with ER and IR, prone and standing ER at 90 degrees of abduction, proprioceptive neuromuscular facilitation (PNF) D2 diagonal-pattern flexion and extension movements, PNF scapular clock, standing high scapular rows, and scaption, flexion, and abduction below 80 degrees and above 120 degrees with ER. Research has shown that lower trapezius activity is relatively low below 90 degrees of scaption, abduction, and flexion, and increases exponentially from 90 to 180 degrees.

One other important muscle, which works in conjunction with the upper and lower trapezius, is the serratus anterior–it too should be addressed when training and rehabbing pitchers. The serratus anterior contributes to all components of normal three-dimensional scapular movement during arm elevation, including upward rotation, posterior tilt, and external rotation. It also helps accelerate the scapula during the acceleration phase of throwing. The serratus anterior even helps stabilize the medial border and inferior angle of the scapula, thus preventing scapular IR (“winging”) and anterior tilt.

To target the serratus anterior, the best exercises include PNF D1 and D2 diagonal-pattern flexion, D2 diagonal-pattern extension, supine scapular protraction, supine upward scapular punch, the military press, push-ups, IR and ER at 90 degrees of abduction, and flexion, abduction, and scaption above 120 degrees with ER. While serratus anterior activity generally increases as the arm is elevated, this also raises subacromial impingement risk, so always use caution when prescribing or supervising elevated-arm exercises.

Of all the serratus anterior exercises, variations of the push-up are among the most simple and beneficial. During standard push-ups, push-ups on knees, and wall push-ups, serratus activity is greater when full scapular protraction occurs after the elbows fully extend, a variation commonly called “push-ups plus.” Compared with the standard push-up, a push-up plus with the feet elevated produces significantly greater serratus anterior activity–an example of how positional challenges are central to making these exercises effective.


Armed with a better understanding of how the key muscles and joints work during the throwing motion, you can make better judgments when designing training programs for healthy pitchers and rehab programs for those returning from injury. The research findings we’ve presented here should assist in prescribing exercise programs that can help your athletes achieve their performance goals.

The overhead thrower is a unique athlete, with unique physical demands and injury risks. Thus, optimal training must be highly specialized, and you shouldn’t be afraid to create a plan that isolates specific muscles for extra recruitment. When your pitchers find that they can produce the same powerful, mechanically sound motion time after time, they’ll thank you for it.

To view references for the research discussed in this article, go to: www.Training-Conditioning.com/references.

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