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Alanna Dark, Karen A Ginn, Mark Halaki. Shoulder Muscle Recruitment Patterns During Commonly Used Rotator Cuff Exercises: An Electomyographic Study. Phys. Ther. 2007; 87(8):1039–1046.

The rotator cuff group, consisting of supraspinatus, infraspinatus, subscapularis, and teres minor, or rotator cuff group, is one of the most commonly injured muscle groups in the body. For clinicians, the understanding of how the rotator cuff muscle group works, is very important in treating shoulder pathologies. The rotator cuff muscles are critical for providing dynamic stability at the shoulder joint; therefore, exercises to improve the function of the rotator cuff are very common in shoulder rehabilitation. The importance of these muscles has brought about many questions concerning about the pattern of recruitment or the rotator cuff muscles compared with that of other shoulder muscles that assist in rotating the shoulder. Over the years, this has been a fairly common subject for research studies, with over 24 such studies being cited in this report alone. The reviewed study, “Shoulder Muscle Recruitment Patterns during Commonly Used Rotator Cuff Exercises: An Electomyographic Study”, sought to investigate how rotator cuff muscles are recruited through a typical rotational exercise and the relationship between the rotator cuff and other shoulder rotational muscles at various loads. Studies have been conducted in the past showing that at high loads, the rotator cuff muscles and other rotational torque-generating muscles are recruited at similar levels (Dark, Ginn, and Halaki, 2007 p. 1040). According to Dark, Ginn, and Halaki (2007), “Because no studies have investigated the differential recruitment of the rotator cuff muscles and other muscles that rotate the shoulder joint at low to moderate resistance levels, it is not known to what extent submaximal exercises involve rotator cuff muscle activity” (Dark, Ginn, Halaki, 2007 p. 1040). There was no clear hypothesis stated, however the indications of this study are important. For example, low loads were found to involve were very little rotator cuff engagement compared to medium or high loads, it would indicate that low load rotator cuff exercises would be minimally affective. For most early stage exercise programs, low load rotator cuff exercise are initially prescribes. Therefore, it is important to establish research evidence supporting this theory.
Eleven women and four men were the subjects for this report with a mean age of 27 years (age range was 18-42 years). All subjects had been free of pain in the non-dominant shoulder for at least two years. The primary instrumentation used for this study was the electromyography. The electromyography employs electrodes which are inserted into the infraspinatus, supraspinatus, subscapularis, latissimus dorsi and pertoralis major. These electrodes detect electricity generated by the muscles during the work load. This instrument can determine how much muscle activation is being employed at any given moment in any place that an electrode is inserted. Along with that, two silver chloride surface electrodes were centered 25 mm apart over the belly of the posterior deltoid. After inserting and placing internal and external electrodes, tape was used to prevent the electrode from accidentally being removed during the experiment. Resistance exercises were used with a pulley system of basic configuration with a load cell placed in series with the rope of the pulley. Data from the electrodes was measured during the exercise movements. A digital camera was placed over head to record the exercises in the transverse plane. This was used to determine the rotational angle between the sagittal plane and the center of the handle by which the subject applied the load, with the center of rotation being the acromion. The speed of the exercises was standardized by setting a