Dynamic shoulder movements in the horizontal plane.
The past three Fine Anatomy articles have examined movements of the shoulder and the shoulder girdle. Because the shoulder is an immensely complex structure, personal trainers must invest a significant amount of time and effort learning its “functional pathologies” and understanding basic anatomy in order to create sound exercise program design.
Over this series, primary movements such as flexion, extension, abduction, adduction and rotation have been discussed. Although there are many other movement factors to consider in assessing the overall function of the shoulder, each of the past three articles provides insight into the movement “potential” the shoulder joint can obtain without obstruction.
This article wraps up the series by taking a look at dynamic shoulder movements in the horizontal plane (arm at 90 degrees from neutral, or 0 degrees from anatomical position). Each of the muscles discussed has already been cited over the course of the series, which has included detailed anatomical illustrations and charts that define muscle origin, action and insertion (see “Resources” on page 38). This article will sum up the dynamic range and “put the pieces together” to explain circumduction of the shoulder, which combines movements in all planes.
Movements of the shoulder girdle in the transverse (horizontal) plane involve movements of the scapula on the thorax. Ideally, the shoulder girdle should move easily backward or forward from neutral (Figures 1–3). If the shoulder girdle is set slightly posterior to neutral or slightly anterior, the movements of the humerus—such as rotation—will be altered owing to both glenohumeral and scapular positioning.
If pectoralis major, pectoralis minor or serratus anterior becomes adaptively shortened, the shoulder girdle (unilaterally or bilaterally) will be set slightly anterior, or forward. This will cause a change in range of motion (ROM) of both the shoulder girdle and the humerus. Assuming this postural stance will limit shoulder ROM; movements will not look ideal, nor will they necessarily be executed properly. Many clients will need exercises broken into smaller motions before they can integrate the movements properly.
Horizontal abduction and adduction are movements in the transverse plane about a longitudinal axis.
Horizontal abduction, also known as horizontal extension, is movement in a lateral and posterior direction 30–40 degrees in range. Posterior deltoid is the primary mover in this plane during repetitive actions. The range of horizontal abduction is greatly affected by the length of pectoralis major. Pectoralis major has a clavicular head and a sternocostal head so, if both heads contract, the humerus is able to produce adduction and medial (internal) rotation of the arm. If this muscle is chronically overused, shortened or restricted, horizontal abduction can be greatly limited.
Horizontal adduction is movement in an anterior and medial direction. The end position for complete horizontal adduction is the same as that for adduction obliquely upward across the body. Normal range in horizontal adduction should be approximately 140 degrees. This range can be tested by simply placing the palm of one hand on top of the opposite shoulder to check if full range can be achieved. Anterior deltoid and pectoralis major are the primary movers of the arm in this motion.
Horizontal flexion and extension are movements of the upper limb in the horizontal plane around a series of vertical axes; these movements involve both the shoulder joint and the scapulothoracic “joint.” The upper limb abducts to 90 degrees in the frontal plane and calls into action supraspinatus, trapezius, serratus anterior and deltoid fibers relating to the acromial region. These muscles work to stabilize the horizontal position. Horizontal flexion (associated with adduction as the arm moves in front of the body) has a range of 140 degrees. Subscapularis, serratus anterior, pectoralis major and pectoralis minor can be recruited for this movement.
Horizontal extension (also associated with adduction as the arm moves toward the body) has a more limited range of 30–40 degrees. This movement is created by the posterior fibers of the deltoid, supraspinatus, infraspinatus, teres major and minor, rhomboids, trapezius and latissimus dorsi (acting as an antagonist-synergist with the deltoid). This movement is ideally executed when the scapulothoracic “joint” is not compromised and glides without restrictions. The horizontal range falls short of 180-degree movement from the extreme positions anteriorly to posteriorly. This movement successively mobilizes the various fibers of the deltoid group—the dominant muscles innervated.
A varying degree of ROM is created depending on the degree of elevation in abduction or flexion. Since the shoulder is a ball-and-socket joint, degree of range will vary depending on the humeral and elbow positions.
In the horizontal plane with the shoulder at 90-degree abduction and the elbow bent at a right angle, internal and external rotation can also strengthen the shoulder (Figures 4a–c). From this position, lateral or external rotation describes a 70-degree arc if shoulder girdle movement is not permitted. A 90-degree arc can be obtained if the scapula is allowed to tilt at end range. Positioning is key for executing rotational movements to strengthen the shoulder joint.
Circumduction consecutively combines the movements of flexion, abduction, extension and adduction as the upper limb circumscribes a cone with its apex at the glenohumeral joint. This movement can be performed in either direction and is used to increase the overall ROM of the shoulder joint. Clients can use their eyes to condition accessibility of the upper limbs by moving the limbs from one extreme position to another with the head fixed in the sagittal plane. Simply put, if clients create circumduction with movement specifically executed by the glenohumeral joint, their field of vision can be their guide to determine range. While maintaining neutral spine as the arm moves in circumduction, clients should always have their hand in full view. Once the hand wanders out of view, they’ll know that a great amount of movement has been recruited in the muscles affecting the scapulothoracic and sternoclavicular joints.
You can help clients with limited ROM to create movements by having them lie prone on a bench where the arms can move freely. You can also have them practice while supine, side-lying or standing to alter the impact of gravity as the angle of the humeral head is changed. If full range cannot be achieved in a standing position without accessory movement from either the head, neck or trunk, working in different positions can often lead to more freedom of ROM and also give clues as to which muscle is inhibiting motion. Circumduction should be smooth in its transitions about the axes. Clients showing compensatory movements to achieve full circumduction need to work toward full range step by step until ideal motion can be achieved. Be creative with movements of circumduction. If a client can’t do these movements standing, try other positions first.
In assigning muscle function, we assume that the arm starts in anatomical position, at the side of the body. In different positions, functional changes occur and may even be reversed. For example, pectoralis major is an arm flexor up to 60 degrees. Beyond 90 degrees, it can no longer move the arm forward or upward. In fact, beyond 90 degrees it begins to function as an extensor, bringing the arm back toward anatomical position. The same idea applies to latissimus dorsi in extension. In cases like these, deltoid tends to “take over” at the extremes of movement as other muscles become ineffective. Abduction of the arm, broadly defined as a movement of the upper limb away from the sagittal plane, is valid only to 90 degrees. Past that point, the upper limb moves toward the body, yet the movement is still termed abduction.
The multiarticular complex of the shoulder is mechanically linked with the potential to function in concert. In practice and training, groups of muscle can work simultaneously with a variable contribution from each joint region, depending on type of movement. Exercises should not always be limited to strict range, as movements of the arms are dynamic.
Work with your clients to achieve a better understanding of their postural positioning and ideal joint ROM. Even a very muscularly strong body can have severe structural faults if positions of joints are never addressed.