Subscription is FREE for qualified healthcare professionals in the US.

Dysfunction and Rehabilitation of the Shoulder

Considerations of muscular relationships in pain management based on Surface Electromyographic (SEMG) Studies.
Page 1 of 4

It is the objective of this article to present a novel view on the diagnosis of shoulder dysfunction and rehabilitation based on the statistical analysis of muscular activity data as noted on surface electromyographic (SEMG) studies of the asymptomatic shoulder muscles.1-3

The human shoulder is a very complex musculoskeletal structure. The anatomy allows it to perform both postural and ballistic functions. Muscular, bony, and joint evolution has changed little from the epoch when early humans were still partially quadrupeds. The clavicle is one of the earliest bones to develop in the fetus.

The shoulder dexterity engram is engrained deep in our motor cortex and related structures. All that one has to do is to observe the ease of ‘four-legged’ movements of infants before they become ‘two legged’ ambulatory. No one ever had to teach infants to move about and explore the surroundings with ease on their four limbs and reach objects with their upper limbs along their way.

The primary bony structures—the scapula and clavicle—are enveloped by nineteen primary muscles.4 While it is possible to classify those muscles by their anatomic location, for a few of them the classification is only partially correct. Thus, the classification could comprise the superior, lateral, anterior. and posterior muscle groups.

The superior shoulder group is comprised of the supraspinatus, levator scapulae, and the upper trapezius. The lateral group is comprised of the deltoid (anterior, middle and posterior) components and coraco-brachialis. The anterior group is comprised of the pectoralis major and minor. The posterior group is comprised of the infraspinatus, subscapularis, teres major and minor, rhomboid major and minor, middle and lower trapezius, latissimus dorsi, and serratus anterior. During motion, these muscles are active and modulate one another’s action via the myofascial components.

The shoulder movements proper also involve myofascial contributions from the contiguous muscles of the neck, back, and upper limb muscles.4,5 Classically, the range of motion (ROM) of the shoulder is comprised of the following segments: abduction, adduction, (anterior) flexion, lateral flexion, posterior flexion, external and internal rotation.

The shoulder movements require energy. The fact that there are so many muscles that participate in any given motion allows for an easy ‘spread’ of the energy consumption, such that no muscle in particular may suffer much from fatigue due to repetitive motion. One objective means of measuring the energy consumption and effort is by SEMG assessment of the shoulder muscles through the ROM in asymptomatic and symptomatic muscles.

Table 1. Muscles of the superior shoulder region: SEMG amplitude potentials
Segments of motion
Muscles Ext Rot Lat Flex Abduction Int Rot Post Flex Ant Flex Avg
Levator Scapulae 33.2 41.3 32.8 35.0 25.5 17.8 30.9
Upper Trapezius 37.0 21.9 25.3 23.9 23.9 14.9 24.5
Supraspinatus 22.9 26.5 22.1 18.7 15.1 15.7 20.2
Average 31.0 29.9 26.7 25.9 21.5 16.1 25.2
Table 2. Muscles of the posterior shoulder region: SEMG amplitude potentials (µV RMS)
Segments of motion
Muscles Ext Rot Abduction Lat Flex Post Flex Int Rot Ant Flex Avg
Rhomboid Major 38.5 34.3 46.9 33.6 44.0 20.0 36.2
Rhomboid Minor 33 41 38.2 18.1 23.8 29.1 30.5
Middle Trapezius 40.4 26.0 31.3 20.8 32.3 13.7 27.4
Infraspinatus 30.3 26.4 22.1 23.8 16.3 27.8 24.5
Latissimus Dorsi 11.1 13.2 7.6 23.3 9.7 11.4 12.7
Lower Trapezius 33.2 28.8 17.5 11.5 9.2 18.4 19.8
Serratus Anteror 10.8 12.1 10.5 15.2 5.2 13.6 11.2
Teres Major 12.7 10.1 7.5 15.0 8.3 7.6 10.2
Teres Minor 10.0 9.4 6.3 9.2 6.2 7.5 8.1
Average 24.4 22.4 20.9 18.9 17.2 16.6 21.1

Testing Protocol

Studies of shoulder muscles were conducted within the limitations of anatomy and symmetry of motion.6 The limitations of these studies include the lack of ability to assess deep muscles such as subscapularis and coraco-brachialis with SEMG (or needle-EMG).6 Also, it is difficult to perform simultaneous symmetrical testing of the adduction movement. Thus, the data presented in this article are exclusive of these limitations.

Last updated on: January 28, 2012
First published on: November 1, 2007