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- Shoulder Elbow
- v.12(3); 2020 Jun
- PMC7285972
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Shoulder Elbow. 2020 Jun; 12(3): 203–211.
Published online 2019 Dec 4. doi:10.1177/1758573219888829
PMCID: PMC7285972
PMID: 32565922
C Ganderton,1,2 R Kinsella,1,3 L Watson,4 and T Pizzari1
Author information Article notes Copyright and License information PMC Disclaimer
Abstract
Background
A simple modification to standard rotator cuff exercises using an additional resistance band around the scapula has been recommended in the clinical setting, postulated to encourage activation of the posterior scapular stabilisers and increase rotator cuff activation. The aim of this clinical laboratory study was to compare scapular and rotator cuff muscle activation between standard and modified exercises.
Methods
Electromyographic data were collected from 10 healthy adults via surface and intramuscular electrodes from the scapular and rotator cuff muscles. Internal and external rotation exercises of the shoulder with the arm abducted to 0°, 45° and 90° were performed using one handheld resistance band (standard) or two bands with the additional band applied to the scapula (modified).
Results
Activation of the trapezii and rhomboid muscles during the modified exercises at 0° and 45° of abduction was significantly greater when compared to the standard exercises (P < 0.05). No significant differences were found in rotator cuff muscle activation.
Discussion
Applying resistance to the posterior scapula increases activation of some scapular stabilising muscles particularly in lower ranges of abduction. This study provides preliminary evidence that this simple modification can elicit greater scapular muscle activity, potentially producing enhanced exercise outcomes with minimal additional effort.
Keywords: electromyography, muscle activation, rehabilitation, scapula, shoulder pain
Introduction
Rotator cuff strengthening exercises are commonly prescribed in shoulder rehabilitation protocols, though there is a lack of consensus for the most effective exercise type and dosage parameters.1,2 The primary focus of shoulder rehabilitation is usually to strengthen the rotator cuff and facilitate normal glenohumeral kinematics. Despite the plethora of exercises to choose from, there is conflicting evidence for the value of many.3
Since the rotator cuff muscles all take their origin from the scapula, a stable scapula is deemed essential for provision of a secure ‘platform’ for optimal rotator cuff function.4 Thus, a focus on scapular muscle activation, to enhance the resting position and dynamic motion of the scapula, is considered an integral component of shoulder rehabilitation protocols.4–8 Yet achieving balanced activation of the scapular stabilisers and co-contraction of the rotator cuff muscles without fatigue and/or compensatory activation of other muscle groups is often difficult for patients to attain.7
To facilitate improved scapular posture and dynamic motion, a simple modification to standard rotator cuff exercises that uses an additional elastic resistance band around the scapula has been recommended in the clinical setting.7,9,10 It is proposed that the resistance offered by the band will encourage activation of the posterior scapular stabilisers with the resultant scapular upward rotation and posterior tilt creating a stable platform from which the rotator cuff muscles can more efficiently generate force.6,11,12
The aim of this study was to determine if internal and external rotation exercises modified by the use of a scapular resistance band increased activation of the scapular muscles (upper, middle and lower trapezius, serratus anterior and rhomboid major) and rotator cuff muscles (supraspinatus, infraspinatus and subscapularis) when compared to standard exercises. It was hypothesised that there would be increased activation of the scapular muscles in the modified exercise as they acted to hold the scapula in position against the band resistance. This in turn could achieve a more optimal glenoid position and enhance the activation of the rotator cuff muscles.4,5,7,8
Methods
The La Trobe University Ethics Committee approved all research procedures reported in this study. The recommendations established by the Strengthening the Reporting of Observational Studies in Epidemiology Statement for reporting observational/cohort studies were followed.13
Participants
Asymptomatic participants were recruited from a sample of convenience from La Trobe University. All participants gave written consent prior to participation. Inclusion criteria were as follows: aged under 35 years (to reduce the impact of potential age-related changes in the shoulder joint), no shoulder or cervical pain, no previous history of shoulder pain, injury or surgery. Exclusion criteria were as follows: allergy to adhesives (EMG electrode placement), inability to read and understand the participant information sheet and consent form, diagnosed with any neurological or rheumatological conditions, pregnant at the time of data collection.
Materials and apparatus
Five intramuscular electrodes consisting of two 75 µm stainless steel, Teflon® coated wires (A-M Systems, Washington, USA) were prepared for each participant as described by Basmajian and Stecko.14 The electrodes were inserted into the supraspinatus, infraspinatus and rhomboid major muscles according to guidelines from Delagi.15 The subscapularis and pectoralis minor muscle electrodes were inserted following guidelines from Németh etal.16
Real-time ultrasound (HDI 3000, Universal Diagnostic Solutions, California) guidance ensured accurate electrode placement. Four DE-3.1 double differential (Delsys Inc.™, Boston, USA) surface electrodes were applied to the three trapezii segments according to the guidelines of Delagi15 and serratus anterior, following guidelines from Geiringer.17 A telemetry-based wireless EMG unit (Delsys Inc.™, Boston, USA) was used to collect muscle activity data. An accelerometer was attached to the participants’ wrist on the side being tested to distinguish the temporal characteristics of each exercise tested.
Procedures
Testing took place in a laboratory setting and was conducted on the dominant arm of each participant. Participants performed eight repetitions of 12 different rotator cuff exercises using one resistance band held in the hand (standard exercise) and two bands: one in the hand and an additional resistance band applied to the scapula (modified exercise).
External rotation contractions
Standard exercises: External rotation of the shoulder with the arm abducted to 0°, 45° and 90° with the resistance of one elastic band (Theraband™) held in the hand. Modified exercises (additional scapular resistance band): External rotation of the shoulder with the arm abducted to 0°, 45° and 90° with the resistance of two elastic bands (Theraband™), one held in the hand and the other wrapped around the scapula (Figure 1(a) to (c)).
Figure 1.
Modified external rotation exercises at (a) 0°, (b) 45° and (c) 90° abduction.
Internal rotation contractions
Standard exercises: Internal rotation of the shoulder with the arm abducted to 0°, 45° and 90° with the resistance of one elastic band (Theraband™) held in the hand. Modified exercises (additional scapular resistance band): Internal rotation of the shoulder with the arm abducted to 0°, 45° and 90° with the resistance of two elastic bands (Theraband™), one held in the hand and the other wrapped around the scapula (Figure 2(a) to (c)).
Figure 2.
Modified internal rotation exercises at (a) 0°, (b) 45° and (c) 90° abduction.
For the scapular resistance band, a taut green band (Theraband™) was looped around the scapula and attached to a pole at the level of the participant’s shoulder. The pole was positioned at a distance of 1 m in front of the participant, thus providing standardised resistance. This band provided resistance encouraging scapular muscle activation and a position of relative scapular retraction. A red elastic resistance band (Theraband™) was attached to a pole at the level of the participant’s wrist and was held in the hand of participants while they performed the rotator cuff contractions for both the standard band and additional band exercises. The exercise sequence was randomised, to prevent order effects, with participants selecting an exercise card from an opaque box. The speed of repetitions was regulated by a metronome set to 60 beats/min (i.e. two beats per repetition). To reduce effects of participant fatigue, there was a minimum 30 s rest between each exercise.
At the conclusion of the exercises, maximum voluntary isometric contractions (MVICs) were performed using four established shoulder normalisation tests18 – the ‘empty can test’ position, the ‘internal rotation 90° test’ position, the ‘flexion 125° test’ position and the ‘palm press’ test position. For each MVIC, the test was conducted uniformly over a 5 s trial period, repeated three times, allowing a 3 min rest period between each trial.
Data analysis
Delsys EMGworks Acquisition software (CMRR >80 dB at 60 Hz; gain of 1000; band pass filtered 20–900 Hz) was used to record the raw EMG signals sampled at 2000 Hz. All EMG signals were then full wave rectified and low pass filtered through a fourth order Butterworth filter at a cut-off frequency of 6 Hz to create a linear envelope. To obtain graphs, data were amplitude normalised to MVICs and time normalised to 100 points.19,20
For the MVICs of each muscle, the highest average intensity (root mean square (RMS)) value was derived from a 600 ms window centred about the highest peak in the linear envelope signal. This value (100%) was compared to the RMS values of average muscle activity from muscle onset to termination during each exercise and expressed as a percentage of the MVIC (%MVIC). Average intensity values were obtained for repetitions 3, 4, 5 and 6 of the 8 repetitions to reduce learning and fatigue effects.21–23
Percentage MVIC values for each muscle were compared between the exercises with or without the additional scapular retraction band. Where data were normally distributed, a paired t-test was performed. For non-normally distributed data, a Wilcoxon signed-rank test was performed. All analyses were performed using SPSS Version 19 (IBM Corp, Chicago, USA) with significance level, P < 0.05. To prevent committing a Type II error in this exploratory study, a Bonferroni adjustment was not performed.24 During data collection, researchers were not blinded to the exercises performed. Following testing, the data analysts (CG and RK) were blinded to the exercise type being analysed. Mean or median muscle intensity (RMS) values for the scapular stabilising muscles (upper/middle/lower trapezius, serratus, anterior and rhomboids) and rotator cuff muscles under all exercise conditions were compared.
Results
Ten participants (five women) with a mean age of 22.8 years (SD 3.1) participated in the study. Significant artefact found in EMG signals from two subjects during testing over two different exercise conditions (45° IR with band and 90° IR without band) precluded inclusion of their raw data in the analysis. The results for the scapular and rotator cuff muscle activation during performance of the standard and additional scapular retraction band exercises are presented in Tables 1 and and22 and are depicted in graphical form in Figures 3 and and44.
Figure 3.
EMG muscle activity during standard and modified external rotation exercises. ER: external rotation.
Figure 4.
EMG muscle activity during standard and modified internal rotation exercises. IR: internal rotation.
Table 1.
%MVC mean, median (interquartile range) and p-value for each muscle during external rotation exercises.
| Muscle | Exercise type | Mean (SD) | Median (IQR) | p-value (p < 0.05) | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 0° | 45° | 90° | 0° | 45° | 90° | 0° | 45° | 90° | ||
| Supraspinatus | Modified | 14.08 (11.84) | 28.20 (16.84) | 43.40 (27.73) | 12.10 (18.92) | 26.18 (27.30) | 37.27 (36.19) | 0.156a | 0.878b | 0.114b |
| Standard | 8.12 (6.85) | 25.22 (13.75) | 29.97 (10.59) | 5.13 (10.65) | 22.16 (21.53) | 30.30 (17.30) | ||||
| Infraspinatus | Modified | 33.52 (19.74) | 41.52 (38.10) | 45.97 (34.67) | 34.39 (34.46) | 30.10 (43.19) | 47.51 (54.27) | 0.799b | 0.944a | 0.508b |
| Standard | 37.91 (25.65) | 42.41 (25.73) | 39.62 (17.63) | 29.16 (29.76) | 42.98 (41.67) | 42.67 (28.26) | ||||
| Subscapularis | Modified | 21.42 (36.03) | 2.25 (2.53) | 2.52 (2.23) | 3.72 (28.74) | 1.52 (3.01) | 2.19 (3.30) | 0.149a | 0.884a | 0.579a |
| Standard | 3.31 (2.38) | 2.38 (2.64) | 2.86 (2.27) | 3.31 (2.39) | 1.35 (3.16) | 1.99 (2.60) | ||||
| Upper trapezius | Modified | 4.82 (3.50) | 9.25 (4.21) | 13.80 (6.81) | 3.38 (3.96) | 7.93 (5.97) | 10.48 (11.90) | 0.075a | 0.386b | 0.902a |
| Standard | 2.60 (1.09) | 8.92 (4.75) | 13.93 (6.72) | 2.28 (2.01) | 7.64 (5.79) | 12.60 (7.59) | ||||
| Middle trapezius | Modified | 17.65 (14.65) | 17.57 (9.44) | 19.66 (11.30) | 8.25 (22.24) | 16.98 (17.98) | 23.54 (7.84) | 0.052a | 0.007b | 0.441b |
| Standard | 7.87 (3.29) | 12.22 (4.84) | 20.24 (7.16) | 7.39 (4.65) | 12.25 (9.44) | 22.32 (5.19) | ||||
| Lower trapezius | Modified | 30.91 (17.84) | 33.06 (20.12) | 40.79 (19.55) | 29.71 (24.62) | 33.30 (33.70) | 37.31 (28.85) | 0.022b | 0.721b | 0.445b |
| Standard | 17.89 (7.05) | 32.51 (21.53) | 36.72 (26.28) | 17.83 (7.66) | 33.74 (34.77) | 26.28 (30.51) | ||||
| Serratus anterior | Modified | 4.22 (2.61) | 4.16 (2.51) | 11.22 (6.69) | 3.66 (4.92) | 3.91 (2.37) | 9.67 (10.51) | 0.285b | 0.267a | 0.508b |
| Standard | 3.45 (2.11) | 4.76 (3.58) | 12.58 (7.36) | 3.37 (2.61) | 3.61 (2.64) | 10.77 (10.42) | ||||
| Rhomboid major | Modified | 42.18 (27.99) | 36.79 (27.05) | 41.30 (24.99) | 33.09 (42.77) | 31.31 (38.75) | 39.49 (45.15) | 0.013b | 0.005b | 0.203b |
| Standard | 25.14 (13.33) | 4.16 (2.51) | 31.81 (30.27) | 23.99 (17.32) | 3.91 (2.37) | 28.21 (32.76) | ||||
Open in a separate window
IQR: interquartile range; MVC: maximal voluntary contraction; SD: standard deviation.
aDerived from a paired t-test.
bDerived from a Wilcoxon signed-rank test.
p-values highlighted in bold are significant.
Table 2.
%MVC mean, median (interquartile range) and p-value for each muscle during internal rotation exercises.
| Muscle | Exercise type | Mean (SD) | Median (IQR) | p-value (p < 0.05) | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 0° | 45° | 90° | 0° | 45° | 90° | 0° | 45° | 90° | ||
| Supraspinatus | Modified | 7.44 (6.75) | 15.44 (8.82) | 14.71 (5.76) | 6.36 (9.23) | 14.80 (13.94) | 15.09 (5.91) | 0.959a | 0.066a | 0.203a |
| Standard | 7.47 (6.73) | 18.71 (12.02) | 11.60 (7.89) | 5.69 (9.41) | 14.50 (16.40) | 10.34 (9.67) | ||||
| Infraspinatus | Modified | 5.84 (4.80) | 9.66 (12.10) | 13.82 (9.65) | 3.84 (6.07) | 6.19 (9.72) | 13.88 (18.43) | 0.247b | 0.681b | 0.681b |
| Standard | 12.40 (14.76) | 10.08 (7.98) | 7.20 (7.11) | 7.84 (10.02) | 9.53 (9.38) | 5.78 (7.86) | ||||
| Subscapularis | Modified | 3.62 (3.98) | 6.99 (7.41) | 10.47 (8.32) | 1.40 (4.50) | 3.24 (12.47) | 13.34 (13.80) | 0.466b | 0.953a | 0.203a |
| Standard | 4.93 (3.38) | 5.95 (3.40) | 15.23 (13.96) | 4.62 (4.88) | 5.41 (3.71) | 13.18 (16.89) | ||||
| Upper trapezius | Modified | 5.27 (3.99) | 5.22 (3.51) | 8.48 (4.57) | 4.09 (7.31) | 4.32 (4.38) | 7.75 (7.71) | 0.047a | 0.293b | 0.303a |
| Standard | 3.98 (2.50) | 5.96 (3.92) | 7.12 (2.77) | 3.37 (3.79) | 4.55 (7.34) | 6.98 (5.23) | ||||
| Middle trapezius | Modified | 9.37 (10.07) | 7.67 (10.01) | 10.86 (7.96) | 2.35 (17.61) | 3.79 (11.40) | 8.03 (16.29) | 0.038b | 0.541b | 0.139a |
| Standard | 4.01 (3.91) | 6.07 (6.16) | 8.93 (7.43) | 1.95 (5.78) | 3.66 (6.23) | 5.23 (11.32) | ||||
| Lower trapezius | Modified | 13.55 (9.62) | 19.36 (15.26) | 23.63 (19.52) | 12.37 (13.70) | 16.80 (27.11) | 16.49 (26.99) | 0.013a | 0.072b | 0.187b |
| Standard | 7.39 (4.03) | 9.88 (13.01) | 15.70 (15.22) | 8.49 (6.95) | 5.85 (6.94) | 9.56 (23.98) | ||||
| Serratus anterior | Modified | 3.17 (1.73) | 3.66 (1.83) | 7.05 (3.01) | 3.04 (2.58) | 3.82 (2.83) | 6.69 (2.84) | 0.799a | 0.139a | 0.308b |
| Standard | 3.25 (2.48) | 4.60 (2.08) | 8.61 (3.45) | 2.89 (2.39) | 4.37 (3.45) | 8.03 (5.58) | ||||
| Rhomboid major | Modified | 20.28 (15.58) | 22.84 (22.49) | 25.79 (25.95) | 18.15 (26.30) | 14.81 (28.07) | 15.78 (34.03) | 0.017a | 0.100b | 0.277b |
| Standard | 10.16 (7.33) | 14.91 (22.87) | 19.95 (28.48) | 10.17 (14.95) | 7.61 (13.28) | 10.27 (23.23) | ||||
Open in a separate window
IQR: interquartile range; MVC: maximal voluntary contraction; SD: standard deviation.
aDerived from a Wilcoxon signed-rank test.
bDerived from a paired t-test.
p-values highlighted in bold are significant.
Activation of the middle (at 0° and 45° of abduction) and lower (at 0° abduction) trapezii and rhomboid muscles (at 0° and 45° of abduction) during the modified external rotation exercises was significantly greater when compared to the standard exercises. Activation of all trapezii segments as well as the rhomboid muscles was significantly greater during the modified internal rotation exercises when compared to the standard internal rotation exercises at 0° of abduction only. No significant differences were found for rotation exercises at 90° abduction for any of the shoulder muscles tested. Overall, no significant differences were found in activation of the rotator cuff muscles or serratus anterior during the modified exercises compared to the standard exercises.
Discussion
The modified scapular band external and internal rotation exercises tested in this study have been recommended in the clinical setting on the assumption that there is improved activation of the posterior scapular stabilisers.7,9,10 The resistance band is thought to encourage a relatively retracted scapula position, creating a stable platform from which the rotator cuff muscles can act more efficiently and generate force.6,11,12
The results of this study suggest that applying resistance to the posterior scapula increases activation of some of the scapular stabilising muscles particularly in the lower ranges of abduction. Trapezii activation, particularly middle trapezius, was significantly increased during the modified internal and external rotation exercises at 0° and 45° abduction. Rhomboid major was significantly increased during performance of the modified external rotation exercises at both 0° and 45° abduction, and the internal rotation exercises at 0° abduction. During early abduction, the trapezius and rhomboids are thought to serve a critical movement and stabilising function in the scapulo-thoracic region,25 with the rhomboids working eccentrically to control the upward rotation motion of the scapula produced by the trapezii.26 The potential downward rotation moment of rhomboids could have a detrimental effect on scapula-humeral motion if not synchronous with the activation of the other scapula muscles. Since rhomboid major (and minor) act to retract the scapula towards the thorax in normal shoulder motion and given the scapular band provided a resistance against retraction, greater rhomboid activity in early abduction range was expected and observed. At 90° abduction, significant differences between the two groups were not observed. At this range, the scapula tends to obtain a position of relative retraction and end-range upward rotation and therefore the scapular stabilising muscles are working to maintain this position, regardless of whether the scapular resistance band is in place.
Although a relatively retracted scapula has been shown to produce greater force generation of the rotator cuff muscles,6,11,12 a significant increase in rotator cuff activation during the modified exercises was not found in this present study. It is conceivable that the rotator cuff muscles in this population of young asymptomatic participants had sufficient activation, so further increases were not required. It is also feasible that the few differences identified within the current population are a result of the population having asymptomatic shoulders, and likely, good scapular and humeral head position and control. Furthermore, the majority of the participants were physiotherapy students, who were likely to be well informed regarding optimal scapular posture regardless of the presence of a scapular resistance band or not, hence performance bias may have been present.
Serratus anterior activity was not found to increase during any of the modified exercises. Overall the activation of this muscle was low across all testing conditions compared to many of the other muscles tested. A primary role of serratus anterior is to posteriorly tilt the scapula, maintaining its inferior border against the thorax as it upwardly rotates.27 The results of this study suggest that either the serratus anterior does not activate a great deal during internal or external rotation at a specific point in shoulder abduction range, or that the method of data collection was not optimal. Indeed, the challenge of recording sensitive and specific data from surface EMG when utilised even in the larger, superficial muscles must be acknowledged.28–30 Several authors have demonstrated under- or over-estimation of muscle activity due to geometric displacement31,32 and crosstalk from adjacent muscles during static and dynamic exercise testing in the scapular, rotator cuff and other synergistic shoulder muscles, including the serratus anterior, infraspinatus, deltoid and latissimus dorsi.31,33–36
The large standard deviations and interquartile ranges seen in this present study highlight the variability in muscle activation between participants. This inherent variability in muscle activation is commonly seen in EMG studies.37 The variability makes it less likely that a statistical difference will be found, even though in the majority of the exercises the average muscle activation was greater in the modified exercise.
Limitations of study
Variability in the data may be attributed to natural differences in the participants’ muscle recruitment, exercise technique and effort with each repetition in each trial. The variability and lack of significant findings may be amplified by the sample size used in this study. In addition, although rest was given between each exercise, the MVICs were undertaken at the conclusion of the exercise protocol and therefore may have been recorded with participants in a fatigued state.
Assessment of the outcomes of testing in ‘normals’ is essential to truly understand subsequent findings in a pathological population.38 This study provides some evidence that the modified external rotation exercise improves activation of the trapezii and rhomboid muscles in a normal population. This study’s conclusions can be used as a premise for further research into the effectiveness of these exercises in a population with shoulder pathologies.
Conclusion
There was a significant increase in the trapezii and rhomboid muscle activity during the scapular resistance band internal and external rotation exercises, in the early ranges of abduction, compared to the standard exercises. The study has provided preliminary evidence for the use of these simple, modified exercises to elicit greater scapular muscle activity while strengthening the rotator cuff in the clinical setting. Future research should evaluate if these modified exercises would be useful as part of a shoulder rehabilitation programme to address rotator cuff muscle dysfunction in a population with shoulder disorders.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.
Ethical Review and Patient Consent
Ethical approval for this study was obtained through La Trobe University Human Research Ethics Committees (HREC 12-014, dated 12/06/2012). Written permission has been obtained from all individuals who participated in this study and/or have been photographed for this manuscript. We thank them for their contribution to this work.
ORCID iD
R Kinsella https://orcid.org/0000-0002-7981-6293
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