Abstract
Background:
Little is known about the optimal exercise intensity and the effects of arm position on elastic resistance exercise. The purpose of this study was to investigate scapular muscle activity in different arm positions utilized during standing elastic resistance exercise.
Hypothesis:
Lower trapezius (LT), serratus anterior (SA), and infraspinatus (IS) muscle activity will vary across arm positions above shoulder level. Also, oscillation resistance exercise will result in increased muscle activity compared with isometric contraction.
Study Design:
Controlled laboratory study.
Level of Evidence:
Level 4.
Methods:
A total of 19 uninjured male collegiate baseball players volunteered to participate in this study. The electromyography (EMG) activity of the LT, upper trapezius (UT), middle deltoid (MD), SA, and IS muscles was determined using surface EMG in 3 arm positions: diagonal pattern 1 (D1), 120° of shoulder abduction (120), and 90° shoulder abduction with external rotation and elbow flexion (90/90) during both isometric contraction and oscillation resistance exercise.
Results:
No difference in EMG activity of the LT muscle was found between the 120 and 90/90 position. However, the 120 position increased UT and MD muscle activity significantly more than those of the 90/90 position. The D1 arm position significantly increased SA muscle activity more than the 120 and 90/90 positions while the LT muscle activity was nearly silent.
Conclusion:
The standing 90/90 position effectively generated both LT and IS muscle EMG activity while minimizing both UT and MD muscle activity.
Clinical Relevance:
The use of oscillation movements under elastic loading can create high muscle activation in the LT muscle without an adverse effect of the humeral head position and scapular rotation.
Keywords: electromyography, lower trapezius, elastic resistance exercise, overhead athletes
The lower trapezius (LT) muscle plays a role in producing the posterior tilt of the scapula, which enables the athlete to maintain the subacromial space width during the late cocking phase of the throwing or serving motion.14,16 Several exercises generate activity in the LT muscle that can be used for overhead athletes: isometric contractions in a prone or quadruped position23,25 and dynamic kinetic link or free motion exercises, such as “robbery” and “lawnmower.”15 The LT muscle can be highly activated with either shoulder abduction or flexion in both the prone and the quadruped positions due to gravity.23,25 The arm position at 120° of glenohumeral joint (GHJ) abduction is in line with the LT muscle fiber orientation.9 Overhead athletes with a symptomatic shoulder should train at or near the position of the cocking phase of the throwing or serving motion in a standing position prior to return to play for specificity purposes.10,11 However, exercises using positions with shoulder abduction must be performed with caution due to hyperactivity of the deltoid muscle, which can conceivably translate the humeral head superiorly, leading to a decrease in subacromial space width.1,13,20
Few formal studies to date have specifically examined the activity of specific scapular muscles using a therapeutic elastic band in the standing position.7,21 No prior study has investigated nor compared the LT and serratus anterior (SA) muscle activity with that of the upper trapezius (UT) and middle deltoid (MD) muscles using elastic resistance exercise in a standing position. Therefore, the purpose of this study was to investigate LT muscle activity in different arm positions to determine which arm position produced the highest levels of LT muscle activity without concomitant increases in the activity of the UT and deltoid muscles using elastic resistance with the athlete in the standing position. This study hypothesized that LT and SA muscle activities would vary with arm positions, and infraspinatus (IS) muscle activity would be reduced in 120° of GHJ abduction compared with 90° of GHJ abduction and external rotation. It was also hypothesized that the application of an oscillation movement would enhance these 2 targeted muscular activities without creating hyperactivity of the UT and MD muscle as compared with an isometric contraction condition.
Methods
During the baseball off-season, 19 male National Collegiate Athletic Association Division I conference baseball athletes (mean height, 183.1 ± 7.0 cm; mean weight, 91.4 ± 12.3 kg; mean age, 20.1 ± 1.3 years) volunteered to participate in this study. All participants gave informed consent to the procedures as approved by the institutional review board of the university prior to testing. All participants were asymptomatic competitive baseball players without neurologic or physiologic deficits in the upper body based on the completion of a preliminary screening questionnaire. All tests were performed in the kinesiology laboratory.
Electrode Placement
Raw electromyography (EMG) amplitudes of the UT, LT, SA, IS, and MD muscles on the dominant-side shoulder were collected. The skin surface was prepared by shaving any hair and vigorously cleaning with an alcohol swab prior to electrode placement to minimize skin impedance. Bipolar surface silver (Ag) EMG electrodes with a bar length of 10 mm, width of 1 mm, and distance of 1 cm between active recording sites (Delsys Bagnoli-8; Delsys Inc) were used. Based on previous research,15,22,23,25,26 electrodes were placed on the center of the muscle belly in line with the muscle fibers for the specific manual muscle test as follows: UT, halfway between the C7 spinous process and the acromion process; LT, at an oblique angle from the scapular spine and just outside of the scapular medial border; SA, below the axilla between the latissimus dorsi and pectoralis major at the level of the scapular inferior angle; MD, below the acromion over the muscle mass on the lateral upper arm; and IS, inferior and parallel to the scapular spine on the lateral aspect over the infrascapular fossa. All electrodes were attached to the body using double-sided tape and secured with surgical tape. The reference electrode was placed between the electrodes of the LT and the IS.
Maximal Voluntary Isometric Contraction
Once the electrodes were secured, participants performed 2 sets of 4-second maximal voluntary isometric contraction (MVIC) for each muscle using the manual muscle testing procedures for normalization of EMG data.25,26 The manual pressure was applied at the wrist by the same examiner for all testing positions. The MVICs of the UT and SA were examined during a resisted scaption exercise with the athlete in the standing position. Participants abducted their arms to 90° of elevation in the scapular plane with the elbows extended resisting downward pressure, whereas for the MD, the MVIC was examined in 90° of shoulder abduction with the elbow flexed. The MVIC of the IS was examined in a prone position on a treatment table with the elbow flexed to 90° and shoulder abducted to 90° and externally rotated to 0°.2 Participants resisted manual pressure applied toward internal rotation. The MVIC of the LT was examined during quadruped shoulder flexion. Participants elevated their arm to 135° of shoulder abduction with the thumb pointed toward the ceiling and the elbow extended in the kneeling quadruped position resisting downward pressure.
Exercise Protocol
All participants performed isometric (ISO) and oscillation (OSC) resistance exercises in 3 arm positions while standing for EMG data collection: (1) shoulder flexion, horizontal adduction, and external rotation with the elbow flexed (D1); (2) 120° of shoulder abduction with the elbow extended (120); and (3) 90° of shoulder abduction and external rotation with the elbow flexed to 90° (90/90) (Figure 1). Both ISO and OSC resistance exercises were used with 3 different intensities measured by percentage elongation of the elastic band (Red CLX, 1.7 kg at 100% elongation; TheraBand) at 0%, 20%, and 40% resistance levels. Both exercises were completed at 3 intensities in each position for 15 seconds. Participants oscillated at a constant pace following a cue from a metronome set at 150 beats per minute. A randomized exercise sequence was used to minimize the effect of motor learning and fatigue for each participant. The primary investigator instructed participants on how to properly perform the exercises for each position before data collection and allowed them to confirm that they understood the required movement and exercise.
Figure 1.
All participants performed isometric and oscillation resistance exercises with an elastic band in 3 arm positions while standing: (a) shoulder flexion, horizontal adduction, and external rotation with elbow flexed (D1); (b) 120° of shoulder abduction with elbow extended (120); and (c) 90° of shoulder abduction and external rotation with elbow flexion to 90° (90/90).
Data Analysis
EMG activities were collected using a data collection program (MP 150 Data Acquisition System; Biopac System) with a sample rate of 1000 Hz. All data were recorded and stored in a computer for off-line analysis. The mean EMG activity of the middle 2 seconds of each 4-second ISO contraction was calculated, and the greater value of the 2 sets was selected to determine the individual’s MVIC. For the isometric and oscillation resistance exercises, the mean EMG activity of the middle 5 seconds was calculated. All data were calculated as root mean squares (RMS), normalized to MVIC of the corresponding muscles, and presented as percentage MVIC (% MVIC).
A 2 × 3 × 3 (exercise × position × intensity) repeated-measures analysis of variance (ANOVA) design was used to determine whether there was any significant difference in RMS values of EMG muscle activity. Also, the Greenhouse-Geisser correction was used to reduce the risk of type I error for the 3-way repeated-measures ANOVA. Where appropriate, the simple main effect and a post hoc Tukey honestly significant difference (HSD) test were used to measure any significant difference and are presented in the results as the main outcome. The level of significance was set at P < 0.05.
Results
Upper Trapezius
The mean values with both D1 and 120 positions were significantly greater than that of the 90/90 position regardless of the exercise intensity (the critical value of the Tukey HSD [DTukey] = 4.88%; P < 0.05), whereas no difference between the 120 and D1 positions was identified at any of the 3 intensities. The mean values at each of the intensities for each of the arm positions are shown in Table 1. In addition, a percentage increase in the mean value of UT EMG by OSC varied depending on the arm position (Table 2).
Table 1.
Mean (SD) upper trapezius (UT), middle deltoid (MD), serratus anterior (SA), and lower trapezius (LT) muscle activity (% maximal voluntary isometric contraction) across 3 different intensities and 3 different arm positions a
| Arm position | UT | MD | ||||
|---|---|---|---|---|---|---|
| 0% | 20% | 40% | 0% | 20% | 40% | |
| D1 | 25.7 (12.2)**† | 30.1 (15.5)**† | 32.9 (16.0)**† | 15.3 (10.7)*† | 17.1 (11.9)† | 18.1 (12.4)*† |
| 120 | 24.4 (10.4)**† | 33.6 (13.3)**† | 37.6 (12.3)**† | 29.2 (14.4)**†† | 40.6 (17.7)**†† | 44.6 (17.0)**†† |
| 90/90 | 14.6 (1.2)**†† | 22.2 (1.7)**†† | 26.5 (2.0)**†† | 14.3 (7.3)*† | 15.9 (7.8)† | 17.8 (8.3)*† |
| Arm position | SA | LT | ||||
| 0% | 20% | 40% | 0% | 20% | 40% | |
| D1 | 51.6 (17.9)**†† | 64.2 (18.8)**†† | 71.1 (20.4)**†† | 6.3 (10.6)†† | 6.6 (11.3)†† | 7.7 (11.7)†† |
| 120 | 26.2 (10.7)† | 28.7 (10.3)† | 28.7 (9.6)† | 31.1 (18.6)**† | 43.8 (18.7)**† | 48.8 (18.4)**† |
| 90/90 | 26.9 (17.3)**† | 30.9 (18.5)**† | 34.5 (19.9)**† | 32.3 (19.6)**† | 43.0 (22.1)**† | 48.1 (21.6)**† |
Intensities consisted of 0%, 20%, and 40% resistance. See text for description of arm positions.
Significant difference across the different arm positions at each intensity (the critical value of the Tukey HSD [DTukey] = 4.88% for UT; 4.80% for MD; 6.73% for SA; 5.80% for LT; P < 0.05).
Significant difference across the different intensities in each arm position (DTukey = 2.74% for UT; 2.05% for MD; 3.13% for SA; 3.21% for LT; P < 0.05).
Table 2.
Mean (SD) upper trapezius muscle activity (% maximal voluntary isometric contraction) between isometric (ISO) and oscillation (OSC) resistance exercises across 3 different arm positions a
| Arm position | ISO | OSC | % Increase |
|---|---|---|---|
| D1 | 24.1 (7.8)*† | 35.1 (18.0)*† | 45.7 |
| 120 | 28.4 (12.3)*† | 35.3 (13.2)*† | 24.4 |
| 90/90 | 19.3 (9.0)**† | 22.9 (13.3)**† | 18.7 |
See text for description of arm positions.
Significant difference between 2 different resistance exercises (P < 0.05).
Significant difference across the different arm position in each resistance exercise (DTukey = 4.74%; P < 0.05).
Middle Deltoid
The mean MD activity values with the 120 position were significantly greater than that of both D1 and 90/90 positions regardless of intensity (DTukey = 4.80%; P < 0.05). The mean values at each intensity for each arm position are shown in Table 1. In addition, the mean value of MD EMG with OSC was increased by 37.3% compared with that of ISO, regardless of arm position and exercise intensity.
Serratus Anterior
The mean value with the D1 position was significantly greater than that of both 120 and 90/90 positions regardless of exercise intensity (DTukey = 6.73%; P < 0.05), whereas no difference was observed between the 120 and 90/90 positions. The mean values at each intensity for each arm position are shown in Table 1. In addition, the mean value of SA EMG with OSC was increased by 37.6% compared with that of ISO, regardless of arm position and exercise intensity.
Lower Trapezius
The mean value of LT EMG with OSC was increased by 58.5% for the 120 position and 55.1% for the 90/90 position compared with that of ISO, regardless of exercise intensity (P < 0.05), whereas no difference was observed for the D1 position. Also, the mean values with both 120 and 90/90 positions were significantly greater than those of D1 position for both ISO and OSC exercises (DTukey = 6.80%; P < 0.05).
The mean values at each of the intensities for both ISO and OSC are shown in Table 3. The mean values for both 120 and 90/90 positions were significantly greater than that of the D1 position regardless of exercise intensity (DTukey = 5.80%; P < 0.05), whereas no difference was observed between the 120 and 90/90 position. The mean values at each intensity for each arm position are shown in Table 1.
Table 3.
Mean (SD) lower trapezius muscle activity (% maximal voluntary isometric contraction) between isometric (ISO) and oscillation (OSC) resistance exercises across 3 different arm positions a
| Intensity | ISO | OSC |
|---|---|---|
| 0% | 15.6 (12.0)**† | 30.8 (24.3)**† |
| 20% | 24.0 (16.7)**† | 38.3 (29.4)*† |
| 40% | 29.4 (21.2)**† | 40.4 (29.4)*† |
See text for description of arm positions.
Significant difference between 2 different resistance exercises at each intensitiy (P < 0.05).
Significant difference across the different intensities for both ISO and OSC (DTukey = 2.52%; P < 0.05).
Infraspinatus
The mean value of IS EMG was significantly increased by 73.0%, 64.1%, and 53.1% at 0%, 20%, and 40% elongation, respectively, with OSC exercise compared with ISO for the 120 position (P < 0.05). Also, the mean value of IS EMG was significantly increased by 126.5%, 103.4%, and 89.7% at 0%, 20%, and 40% elongation, respectively, with OSC exercise compared with ISO for the 90/90 position (P < 0.05). In contrast, no difference was observed in the percentage increase with OSC exercise compared with ISO exercise for the D1 position. The mean values at each intensity for each arm position for both ISO and OSC are shown in Table 4.
Table 4.
Mean (SD) infraspinatus muscle activity (% maximal voluntary isometric contraction) between isometric (ISO) and oscillation (OSC) resistance exercises across 3 different intensities and 3 different arm positions a
| Arm position | ISO | OSC | ||||
|---|---|---|---|---|---|---|
| 0% | 20% | 40% | 0% | 20% | 40% | |
| D1 | 12.4 (5.6)** | 15.9 (6.3)** | 19.2 (8.3)**† | 13.9 (5.7)**† | 17.4 (8.0)*†† | 20.0 (8.5)*†† |
| 120 | 9.6 (4.2)**‡ | 14.8 (6.3)**†‡ | 19.6 (8.4)**†‡ | 16.7 (9.2)**†‡ | 24.2 (12.5)**†† | 30.0 (13.2)**††‡ |
| 90/90 | 13.3 (6.0)**‡ | 20.7 (7.3)**†‡ | 27.0 (10.5)**††‡ | 30.0 (14.6)**††‡ | 42.1 (18.9)**††‡ | 51.1 (20.7)**††‡ |
See text for description of arm positions.
Significant difference between ISO and OSC resistance exercise at each intensity for both 120 and 90/90 position (P < 0.05).
Significant difference across the different arm positions at each intensity for each resistance exercise (the critical value of the Tukey HSD [DTukey] = 5.77%; P < 0.05).
Significant difference across the intensities with each arm position for each resistance exercise (DTukey = 2.93%; P < 0.05).
Discussion
D1 Arm Position
This current study revealed several clinically applicable findings that can be used to assist clinicians in the design and utilization of these exercises for patients with shoulder pathology. The amount of SA EMG activity was greater in this study than that of exercises in scaption, wall slide, and elevation plus external rotation, which ranged between 50% and 60% MVIC.3,18 However, nearly maximal SA EMG activity can be produced in 180° of shoulder flexion with weight loads.19 The windup position of the throwing motion, or lowering the arm from the overhead position, only produced a mild level of SA muscle activity.12
SA muscle activity needs to be improved in patients with subacromial impingement syndrome.17 However, the LT muscle activity was nearly silent in the standing D1 position, leading to the high ratio of UT to LT muscle activity. This finding suggests that anterior tilt and/or internal rotation of the scapula may take place during D1 positioning. Clinicians need to be cautious when using this exercise in athletes with scapular dyskinesis due to muscle imbalance in scapular muscle activity inherent with this movement pattern.6 However, clinicians may recommend the standing D1 arm position with elastic resistance to increase SA muscle activity for those individuals who experience decreased upward rotation in shoulder abduction on clinical evaluation or in evaluations of overhead athletes over the course of a season.24
120 Arm Position
Exercises that produce lower ratios of UT to LT muscle activity can lead to improved scapular kinesis in terms of posterior tilt stability during upward rotation of the scapula.6 Standing 120 arm positioning generated a lower UT/LT ratio than other exercises in previous research.5 These exercises include standing isometrics with dumbbells or a pulley apparatus in the positions of forward flexion, low row, and scaption with external rotation.5 The standing 120 arm position activated the UT muscle significantly more than that of the 90/90 position. Also, the mean value of IS muscle activity was significantly lower in the standing 120 position than that of the standing 90/90 position with both ISO and OSC exercises. The IS muscle contributes to minimizing the superior migration of the humeral head by compressing the humeral head on the glenoid fossa during GHJ abduction.4 Taken together, clinicians should use the standing 120 position with caution in patients and athletes with subacromial impingement syndrome due to hyperactivity patterns of the MD and UT muscles.
90/90 Arm Position
The 90/90 position is recommended in shoulder rehabilitation exercise in a variety of postural positions for overhead athletes.10,27,28 The LT muscle can be nearly maximally activated in the standing 90/90 position using 9.1 kg of surgical tubing resistance,21 compared with the 1.7 kg of resistance with the elastic band used in this study. However, with the larger loading in that study,21 MD muscle activity was increased by 50% MVIC, compared with 17.8% MVIC in this study, which may result in the superior translation of the humeral head. Consequently, clinicians need to minimize the activity of the UT and MD muscles while increasing LT muscle activation during shoulder exercise using the 90/90 position in overhead athletes.6,10
Compared with a variety of the 90/90 exercises, previous studies revealed that reverse catch external rotation plyometric exercise at the 90/90 position with the patient half-kneeling with a 0.5-kg soft-weight medicine ball activated the LT muscle at the moderate level of MVIC (31% MVIC).8 The UT muscle was activated at the mild level of MVIC (17% MVIC).8,11 Likewise, a prone 90/90 external rotation plyometric exercise with a 0.5-kg soft medicine ball at an exercise speed of 160 beats per minute produced a very high level of LT muscle activity (61% MVIC) with a moderate level of UT muscle activity (27% MVIC).8,11 The standing 90/90 position in this study significantly increased the mean value of IS muscle activity compared with the standing 120 position, leading to a greater proposed stabilization of the humeral head during the exercise.6
Limitations
This study included a very homogeneous cohort, all of whom were highly trained collegiate baseball players and had asymptomatic shoulders at the time of data collection. Thus, the findings may limit the generalizability to other populations. Extrapolation of these results to individuals with differing age or levels of performance, shoulder symptoms, or recovering from injury may not be appropriate.
Conclusion
Both the standing 120 and 90/90 positions activated the LT muscle. However, the standing 120 position created high MD muscle activity, which could lead to superior translation of the humeral head, compared with the standing 90/90 position. The standing D1 position produced high levels of SA muscle activation while the exercise resulted in little activation of the LT muscle. This study also showed significant increases in muscle activation using OSC compared with ISO exercise. The results of this study have clinical implications regarding the careful selection of exercise intensity and arm position when using elastic resistance to produce improved scapular stabilization in the late cocking phase of the throwing motion in overhead athletes.
Footnotes
The authors report no potential conflicts of interest in the development and publication of this article.
References
- 1. Bitter NL, Clisby EF, Jones MA, Magarey ME, Jaberzadeh S, Sandow MJ. Relative contributions of infraspinatus and deltoid during external rotation in healthy shoulders. J Shoulder Elbow Surg. 2007;16:563-568. [DOI] [PubMed] [Google Scholar]
- 2. Byram IR, Bushnell BD, Dugger K, Charron K, Harrell FE, Jr, Noonan TJ. Preseason shoulder strength measurements in professional baseball pitchers: identifying players at risk for injury. Am J Sports Med. 2010;38:1375-1382. [DOI] [PubMed] [Google Scholar]
- 3. Castelein B, Cools AM, Parlevliet T, Cagnie B. Modifying the shoulder joint position during shrugging and retraction exercises alters the activation of the medial scapular muscles. Man Ther. 2016;21:250-255. [DOI] [PubMed] [Google Scholar]
- 4. Cools AM, Borms D, Castelein B, Vanderstukken F, Johansson FR. Evidence-based rehabilitation of athletes with glenohumeral instability. Knee Surg Sports Traumatol Arthrosc. 2016;24:382-389. [DOI] [PubMed] [Google Scholar]
- 5. Cools AM, Dewitte V, Lanszweert F, et al. Rehabilitation of scapular muscle balance: which exercises to prescribe? Am J Sports Med. 2007;35:1744-1751. [DOI] [PubMed] [Google Scholar]
- 6. Cools AM, Struyf F, De Mey K, Maenhout A, Castelein B, Cagnie B. Rehabilitation of scapular dyskinesis: from the office worker to the elite overhead athlete. Br J Sports Med. 2014;48:692-697. [DOI] [PubMed] [Google Scholar]
- 7. Decker MJ, Hintermeister RA, Faber KJ, Hawkins RJ. Serratus anterior muscle activity during selected rehabilitation exercises. Am J Sports Med. 1999;27:784-791. [DOI] [PubMed] [Google Scholar]
- 8. DiGiovine NM, Jobe FW, Pink M, Perry J. An electromyographic analysis of the upper extremity in pitching. J Shoulder Elbow Surg. 1992;1:15-25. [DOI] [PubMed] [Google Scholar]
- 9. Ekstrom RA, Donatelli RA, Soderberg GL. Surface electromyographic analysis of exercises for the trapezius and serratus anterior muscles. J Orthop Sports Phys Ther. 2003;33:247-258. [DOI] [PubMed] [Google Scholar]
- 10. Ellenbecker TS, Cools A. Rehabilitation of shoulder impingement syndrome and rotator cuff injuries: an evidence-based review. Br J Sports Med. 2010;44:319-327. [DOI] [PubMed] [Google Scholar]
- 11. Ellenbecker TS, Sueyoshi T, Bailie DS. Muscular activation during plyometric exercises in 90° of glenohumeral joint abduction. Sports Health. 2015;7:75-79. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12. Henning L, Plummer H, Oliver GD. Comparison of scapular muscle activations during three overhead throwing exercises. Int J Sports Phys Ther. 2016;11:108-114. [PMC free article] [PubMed] [Google Scholar]
- 13. Hinterwimmer S, Von Eisenhart-Rothe R, Siebert M, et al. Influence of adducting and abducting muscle forces on the subacromial space width. Med Sci Sports Exerc. 2003;35:2055-2059. [DOI] [PubMed] [Google Scholar]
- 14. Kibler WB, Ludewig PM, McClure PW, Michener LA, Bak K, Sciascia AD. Clinical implications of scapular dyskinesis in shoulder injury: the 2013 consensus statement from the “Scapular Summit.” Br J Sports Med. 2013;47:877-885. [DOI] [PubMed] [Google Scholar]
- 15. Kibler WB, Sciascia AD, Uhl TL, Tambay N, Cunningham T. Electromyographic analysis of specific exercises for scapular control in early phases of shoulder rehabilitation. Am J Sports Med. 2008;36:1789-1798. [DOI] [PubMed] [Google Scholar]
- 16. Konda S, Yanai T, Sakurai S. Scapular rotation to attain the peak shoulder external rotation in tennis serve. Med Sci Sports Exerc. 2010;42:1745-1753. [DOI] [PubMed] [Google Scholar]
- 17. Ludewig PM, Cook TM. Alterations in shoulder kinematics and associated muscle activity in people with symptoms of shoulder impingement. Phys Ther. 2000;80:276-291. [PubMed] [Google Scholar]
- 18. Ludewig PM, Hoff MS, Osowski EE, Meschke SA, Rundquist PJ. Relative balance of serratus anterior and upper trapezius muscle activity during push-up exercises. Am J Sports Med. 2004;32:484-493. [DOI] [PubMed] [Google Scholar]
- 19. Maenhout A, Benzoor M, Werin M, Cools A. Scapular muscle activity in a variety of plyometric exercises. J Electromyogr Kinesiol. 2016;27:39-45. [DOI] [PubMed] [Google Scholar]
- 20. Mura N, O’Driscoll SW, Zobitz ME, et al. The effect of infraspinatus disruption on glenohumeral torque and superior migration of the humeral head: a biomechanical study. J Shoulder Elbow Surg. 2003;12:179-184. [DOI] [PubMed] [Google Scholar]
- 21. Myers JB, Pasquale MR, Laudner KG, Sell TC, Bradley JP, Lephart SM. On-the-field resistance-tubing exercises for throwers: an electromyographic analysis.J Athl Train. 2005;40:15-22. [PMC free article] [PubMed] [Google Scholar]
- 22. Nakamura Y, Tsuruike M, Ellenbecker TS. Electromyographic activity of scapular muscle control in free-motion exercise. J Athl Train. 2016;51:195-204. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 23. Oyama S, Myers JB, Wassinger CA, Lephart SM. Three-dimensional scapular and clavicular kinematics and scapular muscle activity during retraction exercises. J Orthop Sports Phys Ther. 2010;40:169-179. [DOI] [PubMed] [Google Scholar]
- 24. Thomas SJ, Swanik CB, Swanik K, Kelly JD. Change in glenohumeral rotation and scapular position after a Division I collegiate baseball season. J Sport Rehabil. 2013;22:115-121. [DOI] [PubMed] [Google Scholar]
- 25. Tsuruike M, Ellenbecker TS. Serratus anterior and lower trapezius muscle activities during multi-joint isotonic scapular exercises and isometric contractions. J Athl Train. 2015;50:199-210. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 26. Tsuruike M, Ellenbecker TS. Adaptation of muscle activity in scapular dyskinesis test for collegiate baseball players. J Shoulder Elbow Surg. 2016;25:1583-1591. [DOI] [PubMed] [Google Scholar]
- 27. Wilk KE, Arrigo CA, Hooks TR, Andrews JR. Rehabilitation of the overhead throwing athlete: there is more to it than just external rotation/internal rotation strengthening. PM R. 2016;8(3suppl):S78-S90. [DOI] [PubMed] [Google Scholar]
- 28. Wright AA, Hegedus EJ, Tarara DT, Ray SC, Dischiavi SL. Exercise prescription for overhead athletes with shoulder pathology: a systematic review with best evidence synthesis. Br J Sports Med. 2018;52:231-237. [DOI] [PubMed] [Google Scholar]