Author Archives: John Castle

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Deltoid

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The deltoid muscle consists of 3 fiber regions.  The anterior portion flexes and medially rotates Deltoidthe humerus.  The posterior portion extends and laterally rotates the humerus. The middle portion abducts the humerus.  From the rest position, the deltoid generates a superiorly directed vector that pulls the head of the humerus toward the acromion.  The humeral head should not glide superiorly.   If the posterior head of the deltoid has become the dominant lateral rotator, the result is anterior glide of the humeral head during motion.  The humeral head should not glide anteriorly.

If the anterior head if the deltoid has become a dominant medial rotator and/or the subscapularis, a medial rotator, is dominating the lateral rotators, the resting glenohumeral position is one of medial rotation.  The combination of abduction and medial rotation predisposes the subject to an impingement syndrome.

It is essential that the depressors of the humeral head primarily the supraspinatus, infraspinatus, teres minor, and subscapularis adequately offset the proximal pull of the deltoid muscle. Continue reading →

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Supraspinatus

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The supraspinatus muscle abducts and laterally rotates the shoulder, depresses, and stabilizes Post3the humeral head in the glenoid.  Because this muscle passes under the acromion, it is particularly vulnerable to injury when the shoulder is depressed.  If the humeral head glides superiorly, does not glide inferiorly during shoulder flexion and abduction, or does not rotate laterally enough to prevent impingement of the greater tuberosity against the coracoacromial ligament, then the supraspinatus muscle and tendon are exposed to compression forces. Continue reading →

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Teres Minor

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The teres minor muscle has the same role as the infraspinatus, laterally rotating and depressing Post3the head of the humerus.  Shortness or greater stiffness of the lateral rotators relative to the stiffness of the axioscapular muscle (serratus anterior) is common and can contribute to excessive anterior and superior glide of the humeral head.  Restricted posterior glide and excessive anterior glide are factors in shoulder impingement syndromes.

The lateral rotators often become short or stiff and can interfere with the posterior glide of the humeral head.  It is therefore extremely important to monitor their length and strength characteristics. Continue reading →

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Subscapularis

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  The subscapularis muscle medially rotates and depresses the head of the humerus.  The Post3subscap not only depresses the head of the humerus but also pulls it posteriorly, thus offsetting the muscles acting to cause anterior/superior glide of the humerus.  The subscap and the joint capsule together provide anterior glenohumeral stability. Continue reading →

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Latissimus Dorsi

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The latissimus dorsi muscle medially rotates, adducts, extends, and also depresses the shoulder Latissimusgirdle (not the humeral head).  The range of shoulder flexion/elevation is limited when the latissimus dorsi is short.  When acting bilaterally, the latissimus dorsi extends the spine and anteriorly rotates the hips.  If the abdominals are weak, shoulder flexion is compensated for with lumbar spine extension.  Continue reading →

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Pectoralis Major

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The pectoralis major muscle adducts and medially rotates the humerus.  The upper fibers flex andPecMajor horizontally adduct the shoulder.  The lower fibers depress the shoulder girdle through their attachments on the humerus.  A common clinical finding is that the fibers forming the sternal portion of the pec major test short, while the fibers forming the clavicular portion test long.  Continue reading →

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Trapezius

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  • The trapezius muscle adducts and upwardly (laterally) rotates the scapula.Trapezius
  • The upper fibers are more suited for movement, and elevate the scapula.
  • The middle and lower fibers maintain the vertical and horizontal position of the scapula rather than generate torque.  They are better suited for stabilization, working at a constant length to resist protraction of the scapula by the serratus anterior.
  • Some authors suggest that the middle fibers adduct the scapula, while the lower fibers depress the scapula.  Thus, when the upper trap is short and the lower fibers are overstretched and weak the entire shoulder girdle will be elevated, rather than upwardly rotated.
  • When he upper trapezius is short, and the shoulder girdle is posturally elevated, the entire shoulder, including the distal end of the acromiom, should be elevated.
  • If the upper trap is overstretched and weak and the lower fibers are short and facilitated, the shoulder may be depressed.
  • If the scapula fails to elevate during shoulder flexion or abduction, the action of the upper trapezius is considered to be insufficient.
  • If the middle fibers are short and tight, adduction may dominate over abduction.

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Serratus Anterior

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  • The serratus anterior muscle abducts and upwardly (laterally) rotates the scapula and holds the scapula flat against the rib cage.  The upward rotation is produced by the force couple action of the serratus anterior muscle and the trapezius muscle.
  • The serratus anterior is the primary, and only effective abductor of the scapula.
  • Full range of flexion/elevation motion is not possible if the serratus anterior is paralyzed or weak.
  • Impaired control of the scapula by the serratus anterior is common, and results from the serratus being weak, long, short, or altered in the timing of its movement of the scapula.  If the scapula is not correctly positioned during shoulder flexion or abduction the scapulohumeral muscles (rotator cuff) will not be able to maintain their optimal length and tension relationships.
  • Deficient control of the serratus anterior, causing impairment in timing and range of scapular motion, can cause stress at the glenohumeral joint.  This stress results from the incorrect positioning of the glenoid for glenohumeral joint motion when there is insufficient abduction and upward rotation of the scapula.
  • SerratusObservation of the degree of abduction or adduction of the scapula is necessary to distinguish insufficient performance of the trapezius or serratus anterior.
  • Although both muscles are upward rotators, because the trapezius is an adductor and the serratus an abductor, the medial/lateral position of the scapula can be a guide as to which muscle should be emphasized for lengthening or strengthening.
  • The primary indicators of impaired performance are inadequate abduction and inadequate upward rotation of the scapula during shoulder flexion and abduction.

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