Which back muscle inserts into the humerus?

Introduction

Functionally, shoulder muscles are of two types: stabilizing muscles and effector muscles. Stabilizing muscles (A, Fig. 15.1) are relatively small, with insertion tendons that lie close to, or even in, the substance of the fibrous capsule. Therefore they are not capable of causing significant shoulder movement but rather maintain the humeral head in the glenoid fossa. These stabilizing muscles are called the rotator cuff and include supra- and infraspinatus, teres minor and subscapularis. They all originate from the scapula, run partly under the acromial roof and insert on the humeral tubercles.

Effector muscles (B, Fig. 15.1) are much larger, with tendon insertions at a greater distance from the joint. Consequently, they produce powerful movements and are not primarily involved in stabilization. They are the deltoid complex, the pectoralis major, the latissimus dorsi and the teres major.

Although the standard clinical examination tests both muscle groups, the great majority of the positive findings point towards lesions of the rotator cuff, because lesions of the large effector muscles are extremely rare.

Rehabilitation protocol considerations

Strength training for shoulder or neck muscles is sometimes advocated to address postural distortions that contribute to neurovascular compression. Postural retraining should be initiated and routinely reinforced prior to significant strength training activities so dysfunctional patterns are not strengthened or reinforced.

In more severe cases, some of the suggested treatment techniques are not recommended because the neurological symptoms are severe and any additional pressure on the region aggravates the symptoms. In those cases, simply reduce the pressure applied in the techniques and focus on treatment methods such as the MET technique described above that doesn't put additional pressure on the neurovascular structures.

Be sure to treat the entire upper extremity as part of the TOS treatment strategy because there can be multiple regions of nerve entrapment that could be aggravating symptoms.

The neural mobility technique described in C under Pectoralis minor syndrome treatment above should be performed after the entire upper extremity has been treated. Neural mobility procedures are more effective when the soft tissues along the entire path of the nerve are as relaxed and pliable as possible.

GOLF SWING

Several studies have examined shoulder muscle activity during the golf swing.33–37 Jobe and colleagues34,35 and Pink and colleagues37 used male and female professional golfers to study shoulder musculature activity. These authors quantified both shoulder34,35 and scapular36 muscles of both the leading arm (left for a right-handed golfer) and trailing arm (right for a right-handed golfer), and also reported no significant differences during the swing in shoulder EMG between male and female professional golfers.35 The golf swing has been divided into five phases:34–36 take-away, forward swing, acceleration, deceleration, and follow-through. Take-away is the phase from ball address to the end of the backswing; forward swing is from the end of backswing to when the club is horizontal; acceleration is from when the club is horizontal to impact with the ball; deceleration is from ball impact to when the club is horizontal; and follow-through is from when the club is horizontal to the end of the motion.

Shoulder muscle activity during the golf swing is shown in Table 32-7,37 and scapular muscle activity is shown in Table 32-8.36 During the take-away phase, muscle activity is relatively low to moderate, suggesting that lifting the arms and club up during the backswing is not a strenuous activity. The levator scapulae and lower and middle trapezius of the trailing arm exhibit moderate activity during this phase to elevate and upwardly rotate the scapula, and moderate activity from the serratus anterior of the leading arm helps protract and upwardly rotate the scapula. Upper, lower, and middle trapezius activities are highest during this phase compared with the other four phases.

Infraspinatus and supraspinatus activities of the trailing arm are also highest during this phase but only fire approximately 25% of a MVIC, which implies relatively low activity from these rotator cuff muscles throughout the golf swing. This is surprising in part because most shoulder injuries are overuse injuries that typically involve the supraspinatus or infraspinatus.38–41 However, these rotator cuff EMG data are only for the trailing arm, which exhibited less overall rotator cuff activity throughout the swing compared with the leading arm. These data imply that rotator cuff injury risk may be higher in the leading arm, but this conclusion might not be valid because it only takes relative muscle activity into account and not other factors, such as impingement risk between shoulders. Another interesting finding is that anterior, middle, and posterior deltoid activities were all relatively low throughout all phases, implying that these muscles are not used much throughout the swing.

During the forward swing phase, muscle activity was also relatively low to moderate, except there was relatively high activity from the subscapularis, pectoralis major, latissimus dorsi, and serratus anterior of the trailing arm to adduct and internally rotate the trailing arm and protract the scapula. There were also relatively high activity from the rhomboids and middle and lower trapezius of the leading arm to help retract and stabilize the scapula.

Muscle activity during the acceleration phase was higher overall compared with the forward swing phase. The subscapularis, pectoralis major, latissimus dorsi, and serratus anterior of the trailing arm demonstrated high activity during the acceleration phase to continue adducting and internally rotating the trailing arm. These muscles may be the most important power muscles of the upper extremity to help accelerate the arm during the acceleration phase of the downswing. In addition, using a short or long backswing can affect shoulder activity during the acceleration phase. Slightly greater pectoralis major and latissimus dorsi activity has been reported during the acceleration phase when a short backswing was used compared with a long backswing, suggesting that shoulder injury risk might increase over time.33

During the deceleration phase, the subscapularis, pectoralis major, latissimus dorsi, and serratus anterior of the trailing arm continued to demonstrate high activity, although now the muscle action is more eccentric and slightly smaller in magnitude compared with the acceleration phase. Low to moderate activity occurred from the scapular muscles of the leading arm, and high pectoralis major and infraspinatus activity occurred in the leading arm. Muscle activity generally decreased from the deceleration phase to the follow-through phase.

What back muscles insert on the humerus?

What muscles attach to the humerus?

Which of the following is a lower back muscle that inserts on the humerus *?

How many muscles attach to the humerus?