Electromyographic Activity in the Immobilized Shoulder Girdle Musculature During Ipsilateral Kinetic Chain Exercises

Article Outline

• Abstract
• Methods
  • Participants
  • Testing Procedure
    • Cross body rotation
    • Attempted overhead reaching
    • Attempted ipsilateral floor touch
  • Electromyographic Signal Collection and Data Reduction
• Results
• Discussion
  • Study Limitations
• Conclusions
• References
• Copyright

Abstract 

Smith J, Dahm DL, Kotajarvi BR, Boon AJ, Laskowski ER, Jacofsky DJ, Kaufman KR. Electromyographic activity in the immobilized shoulder girdle musculature during ipsilateral kinetic chain exercises.

Objective

To quantify the electromyographic activity in the shoulder girdle musculature during ipsilateral kinetic chain exercises performed in a shoulder immobilizer in asymptomatic men.

Design

Descriptive.

Setting

Motion analysis laboratory at a tertiary care center.

Participants

Five asymptomatic male volunteers, ages 24 to 32 years.

Intervention

Fine-wire (supraspinatus, infraspinatus, upper subscapularis) and surface (deltoids, trapezii, biceps, serratus anterior) electrodes recorded electromyographic activity from each muscle during a split-stance cross-body rotation (twisting to the opposite side at high, mid, and low levels), split stance attempted ipsilateral floor touch, and attempted overhead reach. All movements were initiated from the immobilized scapula and were tested with and without a combined step.

Main Outcome Measure

Mean peak normalized (percentage of maximum voluntary contraction [%MVC]) electromyographic activity of each muscle during each exercise.

Results

For all exercises, biceps and infraspinatus activity remained low (<10% MVC), whereas upper subscapularis activity was moderate to very high (29%−68% MVC). Supraspinatus activity was low (<20% MVC) for all motions except the attempted overhead reach (23% MVC). Serratus electromyographic activity was less than 20% of MVC for all motions and was most responsive to added stepping (23%−136% MVC without stepping vs 24%−199% MVC with stepping). Cross-body rotation at lower heights progressively increased serratus activity while decreasing supraspinatus, upper trapezius, and anterior deltoid activity.

Conclusions

Based on these electromyographic data, selected kinetic chain exercises could potentially be implemented during periods of shoulder immobilization. All exercises examined could potentially be safe after superior labral anteroposterior repair, but not after subscapularis repair. All exercises, with the exception of the attempted overhead reach, could potentially be safe after supraspinatus repair, with or without concomitant infraspinatus repair. Early activation of the serratus anterior could potentially be achieved by performing cross-body rotations, particularly at lower heights.

Key Words: Electromyography, Exercise, Kinetics, Rehabilitation, Shoulder

SHOULDER IMMOBILIZATION is commonly used to protect healing tissues after shoulder injury or surgery. During this period of days to weeks, deconditioning of the immobilized shoulder muscles may result in weakness and loss of normal neuromuscular control.¹, ², ³, ⁴ Conversely, overactivity of immobilized muscles during the acute healing phase may be injurious.¹, ², ⁴, ⁵ In either case, the recovery process may be impeded.⁶, ⁷

Several authors⁷, ⁸, ⁹, ¹⁰ have highlighted the interaction of the shoulder girdle with the core (back, abdomen, and pelvic regions) and lower extremities as part of the kinetic chain. These authors have advocated the use of kinetic chain exercises to reactivate the shoulder girdle musculature, defining kinetic chain exercises as movements that activate multiple upper- and lower-body segements.⁷, ⁸, ⁹, ¹⁰ Such motions include various combinations of stepping, lunging, reaching, and twisting.⁷, ⁸, ⁹, ¹⁰ Previous data from our laboratory have shown that isolated scapular depression and protraction motions performed in a standing position while wearing a shoulder immobilizer can produce levels of electromyographic activity in the serratus anterior and trapezii muscles sufficient enough for strengthening while maintaining low levels of electromyographic activity (<20% maximum voluntary contraction [MVC]) in the supraspinatus, infraspinatus, biceps, and anterior deltoid muscles.¹¹ Based on the evolving knowledge of kinetic chain function, we hypothesized that early shoulder girdle muscle reactivation during immobilization may also be achieved using kinetic chain exercises in which multiple upper- and lower-body segments are moving.⁷, ⁸, ⁹, ¹⁰, ¹²

The primary purpose of the current investigation was to quantify the electromyographic activity in the immobilized shoulder girdle musculature during a series of kinetic chain exercises. Specifically, we were interested in defining kinetic chain exercises that would reactivate the scapular stabilizer muscles in a protected environment while minimizing activation of the healing rotator cuff, anterior deltoid, or biceps brachii muscles in specific clinical circumstances.³, ⁷, ¹¹, ¹² Identifying these kinetic chain exercises would not only facilitate the shoulder rehabilitation process, but would also provide a mechanism to implement total body reconditioning in the acute postoperative or postinjury period.

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Methods 

Participants 

Five healthy, right-hand dominant men, ages 24 to 32 years, volunteered to participate. Subjects were recruited from our institution via advertisement. The first 5 men meeting the following inclusion criteria were enrolled: (1) right-hand dominant, (2) no history of right shoulder or neck injury or pain requiring formal medical treatment or activity modification, (3) full, pain-free, bilateral shoulder range of motion at the time of enrollment, and (4) no contraindications to fine-wire placement or completion of basic shoulder and body movements. The study group was limited to men in order to control for potential sex effects and due to difficulty obtaining unimpeded fine-wire and shoulder immobilizer placement in women wearing sports bras during a pilot investigation performed in our lab. We chose to study 5 subjects for 2 primary reasons. First, the study design was descriptive and reflected the primary purpose of providing the first documented characterization of electromyographic patterns during these exercises performed in a shoulder immobilizer. These data would provide a basis for further comparative research, potentially including symptomatic populations. Second, our previous research examining shoulder muscle activity during contralateral shoulder movements suggested that 5 subjects would be adequate to identify general electromyographic patterns with each of the exercises used in this investigation.¹² For these reasons, it was felt that a preinvestigation power analysis was unnecessary. The institutional review board at Mayo Clinic approved the investigation, and all subjects completed a written informed consent process prior to participation.

Testing Procedure 

Using standard procedures, we placed fine-wire electrodes (length, 30mm; 27 gauge)^a into the right supraspinatus, infraspinatus, and upper subscapularis muscles (USSC), and preamplified surface electrodes were placed onto the right anterior deltoid, middle deltoid, posterior deltoid, upper trapezius, lower trapezius, middle trapezius, serratus anterior, and biceps brachii.¹³, ¹⁴, ¹⁵ Electrode placement was confirmed by visualization of the electromyographic signal during muscle activation, and all leads were secured with adhesive tape. Thereafter the electromyographic activity associated with a maximal voluntary effort was recorded for each test muscle. Using standard manual muscle testing positions, each subject was given instructions to maintain the test position while a single examiner (JS) exerted a maximal displacing force.¹³, ¹⁶ Subjects were instructed to exert a maximal effort to avoid being overcome by the examiner’s force. One practice repetition was completed to ensure subject understanding and confirm the elicitation of a maximal interference pattern on electromyography. Thereafter, each subject completed two 4-second maximal isometric contractions. The peak 1-second electromyographic activity from these contractions was recorded. For data reduction, the electromyographic activity of each muscle’s MVC was determined by subtracting the quiescent signal from the peak 1-second electromyographic activity recorded for that muscle during the two 4-second isometric contractions.¹³, ¹⁶ Quiescent signals were collected in the prone resting position to avoid displacement of the supraspinatus, infraspinatus, and USSC fine-wire electrodes. A single physical therapist (BRK) applied a standard, postoperative shoulder immobilizer^b onto each subject’s right shoulder girdle using a standard technique. The immobilizer consisted of 2 shoulder straps and a forearm cradle which was attached by self-adhesive (Velcro) to the waist piece. The strap position was adjusted using manufacturer guidelines to ensure subject comfort and to achieve a final position in which the humerus lay against the trunk along the mid-axillary line, the elbow flexed to 90°, the forearm supported in the sling, which was attached by self-adhesive to the abdomen, and the wrist and hand free. Although the amount of motion within the immobilizer was not quantified, this methodology was chosen to simulate clinical applications of the device. After immobilizer application, active scapular motions confirmed maintenance of electromyographic signals. Standing resting electromyographic signals were then recorded during relaxed standing in the immobilizer.

Subjects then completed 10 consecutive repetitions of 10 test exercises (5 exercises done statically, 5 exercises done with a combined stepping motion) while electromyographic activity was recorded from the 11 shoulder girdle muscles.

The subject began in split-stance position with left foot forward. The subject attempted to reach with immobilized right shoulder girdle across the body to the left, resulting in a rotational motion. Subjects were instructed to reach as far as possible without losing their balance, then actively return to the starting position, including conscious retraction of the scapula. Three separate cross-body rotation motions were tested: high (attempting to reach 120° over head, or over the left shoulder), mid (attempting to reach directly across the body in a standard twist motion), and low (attempting to reach for the outside of the contralateral left foot) (fig 1). A second set of each cross-body rotation exercises was completed in which the subject started in a reverse split-stance position with the left foot posterior. The subject then stepped forward with the left foot while simultaneously performing the cross-body rotation motion to the left.

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• Fig 1. 

  Cross-body reach at low level. Note how motion is initiated from the immobilized side and multiple body segments are integrated to achieve the motion.

The subject started in a normal standing position. The subject then attempted to reach directly overhead and to the left with the immobilized shoulder girdle while maintaining the body in the coronal plane. Subjects were instructed to reach as far as possible without losing their balance, then actively return to the starting position, including actively depressing their scapulae. The attempted overhead reach with step was completed similarly, with the exception that the subject started with his feet together and then stepped to the left with the left foot to initiate the motion (fig 2).

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• Fig 2. 

  Attempted overhead reach. Model initiates motion from the immobilized side. Note how multiple body segments are allowed to participate, as long as the model stays in the coronal plane.

The subject placed left foot forward into a comfortable split-stance position. The subject then bent directly forward, attempting to touch the floor on the right side of the body with the immobilized right shoulder girdle. The subject stayed in the sagittal plane, without any rotation, as compared with the cross-body rotation exercise. Subjects were instructed to reach as far forward as possible while maintaining the sagittal plane and their balance, and actively return to the starting position using their total body, including scapular retraction. The attempted ipsilateral floor touch with step was performed similarly, with the exception that the subject started in the reverse split-stance position and initiated the motion by stepping forward with the left foot (fig 3).

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• Fig 3. 

  Attempted ipsilateral floor touch. Model initiates motion with the immobilized side. Multiple body segments participate, although the model does not twist (compare with low cross-body reach).

Each of the 5 basic integrated body-shoulder motions (cross-body rotation high, mid, low; attempted overhead reach, attempted ipsilateral floor touch) represent actual or slightly adapted shoulder rehabilitation exercises that have been reported in the literature.⁷, ⁸, ⁹, ¹⁰, ¹⁷ Performing each exercise with and without stepping allowed us to determine whether muscles would react differently during more dynamic movement patterns. Each subject received instruction in each exercise by the primary investigator and was allowed to practice to preference (typically 3−5 repetitions) before data collection. Subjects were instructed to perform all the reaching motions with the immobilized shoulder as if they were reaching with their arm normally. They were instructed to perform each motion as naturally as possible, moving the trunk adjacent body segments to preference to achieve qualitatively smooth motions with the maximal controllable amplitude. All motions were done at the subject’s self-selected speed.

The order of exercises completed by each subject was randomized to control for order effects.

Electromyographic Signal Collection and Data Reduction 

We collected electromyographic signals using an MA300 electromyography system^c and a custom software data acquisition program.^d All electrodes provided a direct-current (surface) or alternating current (fine-wire electrodes) coupled, low gain, high common mode rejection rate (gain, ×20; intensity, 110dB) preamplifier with a double differential input and were connected to a backpack. The backpack was connected to the computer by a single thin, flexible, 2.34mm (3/32in) diameter coaxial cable. The electromyographic signals were collected at 2KHz, then processed using a custom computer program.^e For processing, signals were band-pass filtered at 20 to 1000Hz, rectified, and then integrated using a 1-second moving average window. For each test muscle, the mean peak 1-second electromyographic activity for each test motion was generated, identifying the muscle’s peak 1-second electromyographic activity for each repetition, and thereafter calculating the average of the 10 peak 1-second electromyographic values. The mean peak 1-second electromyographic value was then normalized against the electromyographic activity associated with a maximal voluntary contraction to generate a percentage of MVC. The normalized signals were then averaged across the study population. For descriptive purposes electromyographic activity was categorized as low (≤0% MVC), moderate (21%−40% MVC), high (41%−60% MVC), and very high (>60% MVC).⁵, ¹⁸, ¹⁹, ²⁰

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Results 

Figures 4A and 4B show the mean peak electromyographic activity for the rotator cuff, biceps, and anterior deltoid muscles during each motion. With the exception of the upper subscapularis, there was relatively little variation in mean peak electromyographic activity as a function of exercise. Infraspinatus and biceps brachii activity was uniformly low and responded very little to stepping (infraspinatus, 3%−6% MVC without step vs 3%−7% MVC with step; biceps, 3%−5% MVC with or without step). Anterior deltoid and supraspinatus activity was low (≤20% MVC) for all exercises, with the exception of the supraspinatus during the overhead reach with step (supraspinatus, 23% MVC). In comparison, upper subscapularis activity was uniformly moderate to very high for all exercises (29%−67% MVC without step vs 38%−68% MVC with step). Although stepping generally increased the electromyographic activity for these muscles during any particular exercise, the quantitative changes were minimal (<10% MVC).

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• Fig 4. 

  Peak 1-second normalized electromyographic (EMG) activity from the rotator cuff, biceps, and anterior deltoid muscles (N=5 subjects) during 5 kinetic chain exercises completed (A) without and (B) with stepping. NOTE. Values are mean ± standard error of the mean (SEM). Abbreviations: AD, anterior deltoid; BB, biceps; CBRHN, cross-body reach high no step; CBRHS, same motion with step; CBRLN, cross-body reach low without step; CBRLS, cross-body reach low with step; CBRMN, cross-body reach at medium height without step; CBRMS, cross-body reach at medium height with step; IFTN, attempted ipsilateral floor touch without step; IFTS, attempted ipsilateral floor touch with step; IS, infraspinatus; OHRN, attempted overhead reach without step; OHRS, attempted overhead reach with step; SS, supraspinatus.

Figures 5A and 5B show the mean peak electromyographic activity for the serratus anterior, trapezii, middle deltoid, and posterior deltoid muscles during each motion. Mean peak electromyographic activity was low to moderate (7%−30% MVC) for the trapezii during all exercises and did not vary much between the upper, middle, and lower trapezius. Quantitatively, increased electromyographic activity with stepping was less than 10% MVC for each trapezius muscle for each exercise. In comparison, serratus anterior electromyographic activity varied greatly between exercises and responded more to the addition of stepping. Serratus activity ranged from 23% (high cross-body reach) to 136% of MVC (low cross-body rotation) without stepping, and 24% (attempted overhead reach) to 199% of MVC (low cross-body rotation) during stepping. Stepping increased quantitative electromyographic activity—10% (attempted overhead reach) to 64% (low cross-body rotation). Serratus activity increased as cross-body rotation height decreased, with or without stepping. In contradistinction, supraspinatus, upper trapezius, and anterior deltoid electromyographic activity decreased as cross-body rotation height decreased—the opposite pattern (see fig 4). The low cross-body rotation generated greater serratus electromyographic activity than the attempted ipsilateral floor touch with or without stepping (low cross-body rotation 136% MVC vs attempted ipsilateral floor touch 39% MVC without step; 199% MVC vs 63% MVC with step). Middle and posterior deltoid activity was low (<20% MVC) for all exercises completed with or without a step.

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• Fig 5. 

  Peak 1-second normalized electromyographic activity from serratus anterior and trapezii muscles (N=5 subjects) during 5 kinetic chain exercises completed (A) without and (B) with stepping. NOTE. Values are mean ± SEM. Abbreviations: see fig 4; LT, lower trapezius; MD, middle deltoid; MT, middle trapezius; PD, posterior deltoid; SA, serratus anterior; UT, upper trapezius.

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Discussion 

Shoulder immobilizers are commonly used postinjury and postsurgery to rest and protect healing tissues, particularly the anterior deltoid, supraspinatus, infraspinatus, subscapularis, and/or biceps brachii. Our previous investigation suggested that deliberately performed ipsilateral scapulothoracic motions could be used during shoulder immobilization as part of the acute phase rehabilitation process in selected cases.¹¹ Scapular depression and protraction performed with the immobilized shoulder girdle elicited low levels (<20% MVC) of electromyographic activity in the anterior deltoid, supraspinatus, infraspinatus, and biceps muscles while producing electromyographic levels greater than 20% of MVC in the serratus anterior and trapezii muscles. Electromyographic activity levels less than 20% of MVC fall within the range of electromyographic activity previously reported for Neer phase I supine and upright exercises and are generally regarded as safe during the acute postinjury or postoperative period.⁵, ¹⁸, ¹⁹, ²⁰ However, this previous study was somewhat limited because subjects remained relatively immobile while deliberate scapulothoracic motions were completed. Recent literature has emphasized the interaction of the core and lower-body segments with the shoulder as part of the kinetic chain.⁷, ⁸, ⁹, ¹⁰ Consequently, total body kinetic chain exercises have been advocated during the rehabilitation of people with shoulder injury.⁷, ⁸, ⁹, ¹⁰ The current research expands our previous findings by suggesting that specific kinetic chain exercises originating from the immobilized shoulder girdle may be safely performed during immobilization, whereas others should be avoided in certain clinical situations. From an electromyography standpoint, patients with supraspinatus or infraspinatus injury or repair could potentially safely perform all the exercises examined in this investigation, with the possible exception of the attempted overhead reach with a step (see fig 4). All exercises could be potentially safe for the patient after isolated superior labral anteroposterior (SLAP) repair, whereas none of the exercises studied would be safe for people with subscapularis injury or repair (see fig 4).

In described core stabilization programs, some authors⁷, ⁸, ⁹, ¹⁰ have advocated increasing the demands on the kinetic chain by adding a step to an exercise or by performing cross-body rotations (or reaches) at lower heights versus upper heights. Although these modifications may increase the total body demands of the exercise, these propositions remain theoretical and the proposed modifications did little to change the electromyographic activity in the anterior deltoid, supraspinatus, infraspinatus, and biceps brachii muscles in the current investigation. For example, the quantitative percentage of MVC increase with stepping was less than 10% in all cases except the serratus anterior. Further research is necessary to elucidate the interaction between variations in integrated body motions and the degree of muscle activation about the shoulder.

With respect to the scapular stabilizers, trapezii activity was low to moderate (<30% MVC) regardless of exercise or step, suggesting that the exercises examined provide only minimal activation of the trapezii muscles (see fig 5). However, the important serratus anterior muscle exhibited at least moderate (>20% MVC) electromyographic activity for all exercises (see fig 5). The cross-body rotation at a high or medium height elicited high electromyographic activity (>41% MVC) without a step, increasing to very high (>60% MVC) activity with the addition of a step. In comparison to the supraspinatus and anterior deltoid, the electromyographic activity in the serratus anterior actually increased with lower cross-body rotation heights (see Fig 4, Fig 5). These findings suggest that cross-body rotations at low or medium heights will generate clinically significant electromyographic activity in the serratus anterior, while producing electrophysiologically safe levels of activation in the supraspinatus, infraspinatus, biceps, and anterior deltoid muscles. Furthermore, these same cross-body rotations at lower heights have been proposed as fundamental movements in core conditioning programs for healthy and injured persons.⁷, ⁸, ⁹, ¹⁰

The reason for the uniformly moderate-to-very-high electromyographic activity in the USSC exercises during the kinetic chain exercises is unknown. However, given the known function of the subscapularis as an internal rotator, we hypothesize that our findings may in part be a consequence of an interaction between the immobilization and the method of exercise.¹¹, ¹³, ²¹, ²² During all exercises, the palm of the immobilized upper limb rested on the subject’s abdomen while in the immobilizer. Although the subjects were only instructed to maintain the hand in its starting position, it is possible that each subject started his scapulothoracic exercises by pressing the palm against the abdomen to close the “kinetic chain” and facilitate initiation of the motion from the scapula as instructed.³, ⁷, ⁸, ¹¹, ²³ This maneuver requires isometric internal rotation force generation by the USSC and may account for the electromyographic activity we observed. If this were the case, then performing isolated scapulothoracic exercises in the immobilized shoulder with the hand held away from the abdomen may significantly reduce the USSC electromyographic activity to safe levels. However, the potential effect of this maneuver on the electromyographic activity of the external rotators may be problematic. Therefore, we cannot recommend this modification until further investigation is completed.

The large electromyographic activity elicited in the serratus anterior during some of the motions examined in the current investigation was unexpected and warrant further discussion. These high values may be explained by signal artifact, error in electrode placement, errors in signal processing, or limitations in the methodology used for the normalization process. Although the precise reason for these findings remain indeterminate, we feel that these values are unlikely to be the result of electrode placement or errors in signal processing and data reduction. The methodology used in the current study was the same as that used during our prior investigations of contralateral upper limb and ipsilateral scapulothoracic motions, neither of which produced such high serratus anterior electromyographic values.¹¹, ¹² It is possible that the ipsilateral kinetic chain motions resulted in high amplitude electromyographic artifacts interpreted as muscle signal. However, review of the raw tracings during the investigation failed to support this explanation. Nonetheless, it remains a possibility. Finally, the large serratus electromyographic activity may be explained as a limitation of the normalization techniques used in this investigation. The electromyographic activity elicited during an MVC does not necessarily reflect the full electrophysiologic potential of the muscle. Prior studies have also reported electromyographic activity greater than 100% of an MVC during functional activities.²⁰, ²⁴, ²⁵ Therefore, it is possible that the kinetic chain motions used in the current investigation in fact produce large electromyographic activation in the serratus, much more than is elicited by the current techniques for determining the electromyographic activation of an MVC. Although we used techniques previously described for determining the electromyographic activation of an MVC, no prior investigation has recorded the activity of the serratus during the kinetic chain activities currently studied.¹⁹, ²⁶ Although further investigation may elucidate the source(s) of the high serratus electromyographic activity, we feel it is important to emphasize the differences in serratus electromyographic activity between exercises as reflected in the current and previous studies.

Study Limitations 

Several limitations of this investigation are worthy of note. First, some researchers and clinicians might consider the study population to be relatively small (ie, 5 subjects). However, there is no universally agreed on number of subjects that would be deemed necessary for an investigation such as this. Based on our previous experience using this study model, we felt that 5 subjects would provide an acceptable indication of the “worst case” scenario of electromyographic activity in the muscles of interest, as reflected in the mean peak normalized electromyographic activity.¹¹ At this time, there is no proof that increasing the number of subjects would substantially change our results. Second, the current data were collected in normal subjects. Because this line of research is novel, we felt that characterization of the extent and patterns of electromyographic activity in a relatively homogeneous, asymptomatic population was necessary. The majority of electromyographic research on which physiatrists currently base rehabilitation programs is based on investigation of normal persons.⁵, ¹⁸, ¹⁹, ²⁰, ²¹ Clearly, future investigations targeting symptomatic persons performing shoulder rehabilitation exercises with or without a shoulder immobilizer would advance our understanding of the symptomatic shoulder and potentially facilitate refinement of our rehabilitation programs. Third, we recognize that there may have been some variability in the fit of the shoulder immobilizer between the 5 subjects. This variability may have resulted in more or less motion, and consequent changes in muscular activity, in any particular subject. However, we wanted to simulate the clinical conditions of shoulder immobilization as currently used in the postoperative or postinjury setting. Therefore, all the immobilizers were applied by a skilled physical therapist, following manufacturer guidelines, to ensure the best fit for each subject. We admit that some motion likely did occur in the immobilizers—it was easily seen and indirectly reflected in the electromyographic activity in the current and prior investigations. Although the shoulder was not truly “immobilized” we would contend that our methods of application reflect the same extent of “immobilization” (or lack thereof) that occurs with the use of these devices in the clinical setting. Finally, the current study focused on peak electromyographic activity, with particular reference to determining which exercises may be unsafe versus safe from an electromyography perspective based on previously published guidelines. All of the exercises exhibited phasic patterns of electromyographic activity for the majority of muscles. However, the methodology of the current study, in the context of its primary purpose, did not include supplementary motion analysis to divide each motion into phases. Our primary concern was the highest average level of muscle activation that could occur during the entire motion itself. Further delineation of the pattern of activation may facilitate refinement of the motions used herein and warrants consideration for future investigation.

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Conclusions 

The current data suggest that early activation of the immobilized shoulder girdle musculature could potentially be safely achieved by performing specific kinetic chain exercises. The serratus anterior is perhaps the most important scapular stabilizer muscle.⁷, ⁸, ⁹, ²³ Our results indicate that among the exercises currently investigated, cross-body rotations are best to achieve early activation of the serratus anterior. Although somewhat more selective serratus activity may be obtained by performing the cross-body rotations at lower heights and/or adding a step, further investigation with respect to these relationships is required before firm conclusions can be made. In general, the currently studied exercises activate the serratus more than our previously studied isolated scapulothoracic elevation and depression exercises, while simultaneously offering the advantages of an integrated kinetic chain movement.¹¹ None of the exercises studied herein produced large electromyographic activity in the lower trapezius, perhaps the second most important scapular stabilizer.⁷, ⁸, ⁹, ²³ Consequently, we suggest reactivating the lower trapezius during immobilization via cross-body reaches at shoulder height performed with the unaffected, contralateral upper limb.¹² From the standpoint of implementing kinetic chain exercises into a total body conditioning program during a period of shoulder immobilization, all of the exercises studied herein could potentially be considered electrophysiologically “safe” after supraspinatus repair, infraspinatus repair, SLAP lesion repair, or anterior deltoid takedown, with the exception of the supraspinatus during an attempted overhead reach with a step. Conversely, none of these exercises as performed in this investigation can be recommended after subscapularis repair. Further research is warranted to confirm these findings in postoperative patients and potentially to refine the exercise movements via a detailed analysis of electromyographic patterns throughout each exercise motion.

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• a Bird & Cronin Inc, 1200 Trapp Rd, Eagan, MN 55121.
• b Nicolet Biomedical, 5255 Verona Rd, Bldg 2, Madison, WI 53711-4495.
• c Motion Lab Systems, 15045 Old Hammond Hwy, Baton Rouge, LA 70816-1244.
• d LabView 6.1; National Instruments Corp, 11500 N Mopac Expwy, Austin, TX 78759-3504.
• e Matlab 6.0; The MathWorks Inc, 3 Apple Hill Dr, Natick, MA 01760-2098.