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Comparison of electromyographic activity of the lower trapezius and serratus anterior muscle in different arm-lifting scapular posterior tilt exercises
Physical Therapy in Sport 13 (2012) 227e232
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Original research
Comparison of electromyographic activity of the lower trapezius and serratus anterior muscle in different arm-lifting scapular posterior tilt exercises Sung-min Ha a, Oh-yun Kwon b, *, Heon-seock Cynn c, Won-hwee Lee a, Kyue-nam Park a, Si-hyun Kim a, Do-young Jung d a
Department of Rehabilitation Therapy, Graduate School of Yonsei University, Wonju, Republic of Korea Department of Physical Therapy, College of Health Science, Laboratory of Kinetic Ergocise Based on Movement Analysis, Yonsei University, 234 Maeji-ri, Heungeop-myeon, Wonju, Kangwon-do 220-710, Republic of Korea c Department of Physical Therapy, College of Health Science, Yonsei University, Wonju, Republic of Korea d Department of Physical Therapy, College of Tourism & Health, Joongbu University, 101 Daehak-ro, Chubu-myeon, Geumsan-gun, Chungnam, Republic of Korea b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 February 2011 Received in revised form 21 September 2011 Accepted 9 November 2011
Objective: To determine the most effective exercise to specifically activate the scapular posterior tilting muscles by comparing muscle activity generated by different exercises (wall facing arm lift, prone arm lift, backward rocking arm lift, backward rocking diagonal arm lift). Design: Repeated-measure within-subject intervention. Participants: The subjects were 20 healthy young men and women. Main outcome measures: Lower trapezius (LT) and serratus anterior (SA) muscle activity was measured when subjects performed the four exercises. Results: Muscle activity was significantly different among the four exercise positions (p < 0.05). The backward rocking diagonal arm lift elicited significantly greater activity in the LT muscle than did the other exercises (p < 0.05). The backward rocking arm lift showed significantly more activity in the SA muscle than did the other exercises (p < 0.05). Conclusions: Clinicians can use these results to develop scapular posterior tilting exercises that specifically activate the target muscle. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: Arm lift Lower trapezius Scapular posterior tilting Serratus anterior
1. Introduction When elevating the arm overhead, the normal scapula undergoes a pattern of upward rotation (45e60 ), external rotation (15e35 ), and posterior tilting (20e40 ) (Escamilla, Yamashiro, Paulos, & Andrews, 2009; Ludewig, Cook, & Nawoczenski, 1996). To complete, 180 of humeral elevation, the scapula should depress, slightly adduct, and tilt posteriorly at the end-range of scapular upward rotation (Sahrmann, 2002). Scapular posterior tilt (SPT) is the movement of the coracoid process in a posterior and cranial direction while the inferior angle of the scapula moves in an anterior and caudal direction (Clarkson, 2005). During arm elevation, SPT occurs about a medial-lateral axis of the scapula, with the
* Corresponding author. Tel.: þ82 33 760 2721; fax: þ82 33 760 2496. E-mail addresses: [email protected] (S.-m. Ha), [email protected] (O.-y. Kwon), [email protected] (H.-s. Cynn), [email protected] (W.-h. Lee), [email protected] (K.-n. Park), [email protected] (S.-h. Kim), ptsports@ hotmail.com (D.-y. Jung). 1466-853X/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ptsp.2011.11.002
inferior angle moving anteriorly (Michener, McClure, & Karduna, 2003), which occurs primarily after 90 and increases sharply at the end-range (Hammer, 2006). SPT may be important in allowing the humeral head and rotator cuff tendons to clear the anterior aspect of the acromion during arm elevation (Escamilla et al., 2009). In particular, athletes or workers involved in overhead activity with abnormal scapular movement at the extremes of humeral elevation are likely to develop shoulder conditions such as subacromial impingement (SI) and glenohumeral instability (Ludewig et al., 1996; McQuade, Dawson, & Smidt, 1998; Warner, Micheli, Arslanian, Kennedy, & Kennedy, 1992). Subjects with SI have approximately 10 less posterior tilt than asymptomatic subjects (Lukasiewicz, McClure, & Michener, 1999). Coordination of SPT muscles is important to prevent abnormal scapular movement and pain during elevation of the arm overhead (Solem-Bertoft, Thuomas, & Westerberg, 1993). The main muscles thought to facilitate SPT are the LT (lower trapezius) and SA (Serratus anterior) (Ebaugh, McClure, & Karduna,
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2005). These muscles are paired to form an important force couple that controls SPT, which is important for widening the subacromial space during overhead activities to prevent impingement of the subacromial tissues (Michener & Leggin, 2001; Solem-Bertoft et al., 1993). A change in the LT and SA muscle function influences SPT and is associated with poor shoulder function and chronic SI (Cools, Witvrouw, Declercq, Danneels, & Cambier, 2003; Kibler & McMullen, 2003). Furthermore, reduction in the force generation of the SPT muscles increases the potential for developing SI syndrome (Ludewig & Cook, 2000; Wuelker, Wirth, Plitz, & Roetman, 1995). Many studies have addressed strengthening exercises of the LT and SA muscle to treat shoulder dysfunction (Arlotta, LoVasco, & McLean, 2011; Ekstrom, Donatelli, & Soderberg, 2003; Hardwick, Beebe, McDonnell, & Lang, 2006; Pontillo, Orishimo, Kremenic, McHugh, Mullaney, & Tyler, 2007). SA muscle activity increases in a linear fashion with arm elevation (Kibler, Sciascia, Uhl, Tambay, & Cunningham, 2008; Ludewig et al., 1996). Conversely, LT muscle activity tends to be low at less than 90 of scaption, abduction, and flexion, and then increases exponentially from 90 to 180 (Hardwick et al., 2006; Smith et al., 2006). Ekstrom et al. (2003) reported that prone overhead arm raise in line with the LT muscle produced maximum activity in the LT muscle. Selective strengthening of the muscles that facilitate SPT is important for rehabilitation of scapular movement impairment; there are plenty of studies available to help clinicians develop effective programs to exercise these muscles (Decker, Hintermeister, Faber, & Hawkins, 1999; Ekstrom et al., 2003; Ekstrom, Soderberg, & Donatelli, 2005; Hardwick et al., 2006; Kibler, 1998; Oyama, Myers, Wassinger, & Lephart, 2010). Effective exercise positions are based on what is known of the functional anatomy and biomechanics of the shoulder complex, previous electromyography (EMG) studies, and clinical experience (Ballantyne et al., 1993). Recently, clinicians and researchers have focused on activation of the LT and SA muscles for normal scapular upward rotation at arm elevation angles above 90 (Decker et al., 1999; Ekstrom et al., 2003, 2005; Hardwick et al., 2006; Kibler, 1998). Representative exercises include the wall facing arm lift, scapular plane shoulder elevation, and overhead arm raise (Decker et al., 1999; Ekstrom et al., 2003; Hardwick et al., 2006; Townsend, Jobe, Pink, & Perry, 1991). Hardwick et al. (2006) reported that SA activity significantly increased with increasing humeral elevation angle (90 , 120 , and 140 ), with no significant differences between the wall slide (37.1e75.4% MVIC) and scapular plane shoulder elevation exercises (41.1e82.4% MVIC). Ekstrom et al. (2003) found the SA muscle activity was significantly higher in the scapular plane shoulder elevation exercises (96% MVIC) above 120 than below 80 , and the overhead arm raise in line with LT muscle fibers was the highest level of LT muscle activity (97% MVIC). Oyama et al. (2010) reported that LT activity (72% MVIC) was highest in 120 shoulder abduction with external rotation (thumb pointing toward ceiling) among 6 scapular retraction exercises. The stabilization of spine, posture of the thorax and shoulder abduction angle may affect SPT and upper extremity movement (Kebaetse, McClure, & Pratt 1999; Lewis, Wright, & Green, 2005; Sahrmann, 2010). To our knowledge, no reported study has quantified activity in the LT and SA muscles at the final stage of scapular upward rotation (i.e., during SPT) during different arm-lifting SPT exercises. The present study compared the muscle activity during the wall facing arm lift (WAL), prone arm lift (PAL), backward rocking arm lift (BRAL), and backward rocking diagonal arm lift (BRDAL) exercises to determine the most effective exercise for activating the LT and SA muscles. We hypothesized that activity of the LT and SA muscles would differ among the four arm-lifting SPT exercises.
2. Methods 2.1. Subjects Twenty healthy young subjects (10 men, 10 women) participated in this study (Table 1). The inclusion criteria were 1) the subject was able to comfortably perform full flexion in the sagittal plane, full abduction in the frontal plane, and full scaption in the scapular plane; 2) the pectoralis minor, levator scapulae, and rhomboid muscles were within the normal length using muscle length tests (Phil, Clare, & Robert, 2010; Sahrmann, 2002). The exclusion criteria were current shoulder pain or shoulder surgery and history of neurological, musculoskeletal, or cardiopulmonary disease that could interfere with shoulder motion in the testing positions. The principal investigator explained the procedure to the subjects in detail prior to the experiment and all subjects signed an informed consent form. This study was approved by the Yonsei University Wonju Campus Human Studies Committee. 2.2. Instrumentation EMG data were collected using a Noraxon TeleMyo 2400T and analyzed using MyoResearch Master Edition 1.06 XP software (Noraxon, Scottsdale, AZ, USA). The electrode sites was shaved and cleaned with rubbing alcohol. Surface electrode pairs were positioned at an interelectrode distance of 2 cm. The reference electrode was placed on the ipsilateral clavicle. EMG data were collected for the LT muscle (placed at an oblique vertical angle with one electrode superior and one inferior to a point 5 cm inferomedial from the root of the spine of the scapula) and the SA muscle (placed vertically along the mid-axillary line at rib levels 6e8) (Cram, Kasman, & Holtz, 1998). The sampling rate was 1000 Hz. A bandpass filter between 20 and 300 Hz was used. EMG data were processed into the root-mean-square (RMS) value, which was calculated from 50-ms data points of windows. 2.3. Procedures The dominant arm (the preferred arm when performing eating and writing tasks) was used in all tests (Yoshizaki, Hamada, Tamai, Sahara, Fujiwara, & Fujimoto, 2009). All subjects reported the right arm as their dominant arm. EMG activity in the LT and SA muscles was tested during four different exercises. A target bar was used to control the angle of shoulder flexion in each exercise. The target bar distance was determined by a vertical line from the wall to the subject’s earlobe in the WAL exercise position. The target bar was placed at this same distance from the surface of the therapeutic table in the PAL, BRAL, and BRDAL exercises. These exercises distinguished by exercise position (standing, prone, and backward rocking), and shoulder abduction angle (180 , and 145 ). 2.4. Wall facing arm lift (WAL) Hardwick et al. (2006) and Sahrmann (2002) described the wall slide exercise. The subject was required to stand facing the wall and contact it from nose to knees with feet shoulder-width apart. In the starting position, the ulnar border of the forearms and medial side Table 1 Descriptive data for participants in this study (n ¼ 20). Variable
ALL
Male (n ¼ 10)
Female (n ¼ 10)
Age (y) Height (cm) Mass (kg)
23.1 1.8 168.5 6.3 58.4 6.8
23.6 2.2 173.7 4.2 64.0 4.5
22.6 1.3 163.2 2.5 52.8 2.6
Values are expressed as mean (SD).
S.-m. Ha et al. / Physical Therapy in Sport 13 (2012) 227e232
of the humerus were in contact with the wall, and shoulder abducted 90 with elbow flexed 90 . The subjects were instructed to slide their arms up the wall. The sliding movement was ended when the shoulder reached 145 of abduction. The subject was then instructed to lift both hands with elbows extended until the radial border of the wrist slightly touched without pushing the target bar and maintained the arm position (Fig. 1A). 2.5. Prone arm lift (PAL) The subject was placed in the prone position. Using a goniometer, the humerus was aligned diagonally overhead with shoulder abduction of 145 and the forearm was in the neutral position. The subjects were asked to place the non-dominant hand under the forehead and push slightly on the forehead with the dorsum of their hand to stabilize the neck and thoracic spine. The subject was then instructed to lift the dominant arm with elbow extended until the radial border of the wrist slightly touched without pushing the target bar and maintained the arm position, which was placed at the same distance used in the WAL exercise (Ekstrom et al., 2003) (Fig. 1B). 2.6. Backward rocking arm lift (BRAL) We invented the backward rocking arm lift exercise. Initially, the subjects were placed in the quadruped position and instructed to rock backward slowly until the buttocks touched both heels. The subjects were asked to place the non-dominant hand under the forehead and push slightly on the forehead with the dorsum of the hand to stabilize the neck and thoracic spine. The principal investigator abducted the subject’s dominant shoulder to 180 using a goniometer. The subject was then instructed to lift the dominant arm until the radial border of the wrist slightly touched without pushing the target bar and maintained the arm position, which was located in a predetermined position (Fig. 1C). 2.7. Backward rocking diagonal arm lift (BRDAL) The subjects were placed in the quadruped position and instructed to rock backward slowly, and the head was positioned as in the BRAL exercise. The shoulder was abducted to 145 by the
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principal investigator and the subject was instructed to lift the dominant arm with the elbow extended until the radial border of the wrist slightly touched without pushing the target bar and maintained the arm position, which was located in the predetermined position (Fig. 1D). Subjects were familiarized with the four arm-lifting SPT exercises during a 30 min period prior to testing. During the familiarization period, the principal investigator instructed the subjects to move their dominant arm until the radial border of the wrist touched the target bar, which was located in a predetermined position for each exercise. The familiarization period was completed when the subject was able to maintain the four exercise positions for 5 s. All of the subjects were comfortable after the familiarization period, and none reported fatigue. A 15 min rest period was allowed after the familiarization period before data collection began.
2.8. Data collection and processing The order of testing was randomized using the random number generator in Microsoft Excel (Microsoft Corp., Redmond, WA, USA). The EMG data were normalized by calculating the mean RMS of three trials of maximal voluntary isometric contraction (MVIC) for each muscle. We used the manual muscle testing positions recommended by Kendall and McCreary (2005) for measuring MVIC. LT muscle activity was tested in the prone position; the subject’s arm was placed diagonally overhead, in line with the lower fibers of the trapezius muscle during external rotation, while resistance was applied distal to the elbow. The SA muscle was tested while the subject was seated on a treatment table with no back support. The shoulder was internally rotated and abducted to 125 in the scapular plane, while resistance was applied proximal to the subject’s elbow by the principal investigator. Each contraction was held for 6 s with maximal effort against manual resistance. The first and last second of the EMG data from each MVIC trial were discarded, and the remaining 4 s of data were used (De Oliveira, De Morais Carvalho, & De Brum, 2008; Vezina & Hubley-Kozey, 2000). Three repetitions of each test were performed, with a 2 min rest interval between repetitions to minimize muscle fatigue (Vera-Garcia, Moreside, & McGill, 2010). The mean MVIC value of the three trials was calculated.
Fig. 1. Type of exercise (A: Wall facing arm lift, B: Prone arm lift, C: Backward rocking arm lift, D: Backward rocking diagonal arm lift).
S.-m. Ha et al. / Physical Therapy in Sport 13 (2012) 227e232
*
Each isometric arm-lifting exercise was performed for 6 s; the first and last second of each exercise trial were discarded, and the remaining 4 s of EMG data were used (De Oliveira et al., 2008; Vezina, & Hubley-Kozey, 2000). The mean of three trials for each arm-lifting exercise was analyzed. The participants were allowed to rest for 2 min between trials, and 3 min between the different exercises positions (De Mey, Cagnie, Danneels, Cools, & Van de Velde, 2009; Lehman, MacMillan, MacIntyre, Chivers, & Fluter, 2006). The data for each trial were expressed as a percentage of the calculated mean RMS of the MVIC (% MVIC), and the mean % MVIC of the three trials was used in the analysis.
*
* 70
*
*
60
%MVIC
50 40 30 20
2.9. Data analysis and statistics
10
B
B
RD
A
L
R AL
L
L
0
W A
A one-way repeated-measure analysis of variance (ANOVA) was used to test for differences in LT and SA muscle activities among the four arm-lifting SPT exercises. Significant main effects were followed up using the Bonferroni post-hoc test. The Statistical Package for the Social Sciences version 12 (SPSS Inc., Chicago, IL, USA) was used to conduct the statistical tests, and p-values <0.05 were deemed statistically significant.
PA
230
Exercise Type Fig. 2. Comparison of the lower trapezius muscle activity among four different exercises.
3. Results The normalized EMG data and the results of the statistical analyses are shown in Table 2. LT muscle activity was significantly higher when performing the BRDAL compared to the other exercises (Fig. 2). The LT muscle activity is shown in Table 2. It increased in the order of WAL < BRAL < PAL < BRDAL (p < 0.05) (Fig. 2). LT muscle activity was significantly lower during the WAL exercise than during the other exercises (p < 0.05). LT muscle activity did not differ significantly different between the PAL and BRAL exercises. SA muscle activity was significantly greater when performing the BRAL exercise than during the other exercises (p < 0.05) (Fig. 3). SA muscle activity did not differ significantly among the WAL, PAL, and BRDAL exercises. 4. Discussion We investigated muscle activity in the LT and SA muscles during four different arm-lifting SPT exercises. Sufficient upward rotation and posterior tilting of the scapula are essential components for throwing and overhead activities (Borsa, Timmons, & Sauers, 2003; Hammer, 2006; McClure, Bialker, Neff, Williams, & Karduna, 2004). We believe that our study is the first to investigate activity of the LT and SA muscles at the end-range of scapular upward rotation during different arm-lifting SPT exercises. For the LT, our results showed that the LT muscle activity was significantly greater during the BRDAL exercise than during the PAL, BRAL, or WAL exercises (p < 0.05). Previous studies using Kendall’s instructions (Kendall, & McCreary, 2005) for positioning the LT during muscle testing found that the “diagonal overhead” arm
raised in line with the lower part of the trapezius in the prone position produced the maximum mean EMG activity (97% MVIC) in this muscle (Ekstrom et al., 2003). Oyama et al. (2010) reported that LT activity (72% MVIC) was highest in 120 shoulder abduction with external rotation (thumb pointing toward ceiling) among 6 scapular retraction exercises. The results of our study are similar to those of previous studies showing that LT muscle activity is highest when the shoulder is abducted to 145 . Moseley, Jobe, Pink, Perry, and Tibone (1992) reported that, of the 16 exercises tested, the prone rowing exercise with shoulder abduction below 90 was the most effective in activating the LT muscle. Prone external rotation at 90 abduction has been reported to increase LT muscle activity significantly more than the empty can exercise (Ballantyne et al., 1993). It is difficult to compare the results of our study directly with those of previous studies because of the different exercise positions and protocols. We found that BRDAL elicited a higher level of LT muscle activity (63.49 %MVIC) than did the other exercises (PAL: 53.71 18.43% MVIC, BRAL: 47.99 20.87% MVIC, WAL: 25.88 21.23% MVIC), whereas the WAL position elicited the lowest level of LT muscle activity. The BRDAL, PAL, and BRAL exercises were performed in antigravity positions, which may explain why the WAL position elicited the least LT muscle activity of the four arm-lifting SPT exercises. In the present study, LT muscle activity elicited by BRAL was less than that elicited by BRDAL and PAL. McMahon, Jobe, Pink, Brault, and Perry (1996) reported that LT muscle activity was greater at 145 shoulder abduction than at 180 in the prone position. The BRAL exercise was performed at 180 shoulder abduction in the present study. Unlike the WAL and PAL exercises, the BRDAL exercise was performed with the neck and trunk stabilized by the backward rocking position. Position of
Table 2 Mean (SD) EMG activation expressed as a percentage of maximal voluntary isometric contraction for each exercise. Muscle
Exercise a
b
c
25.88 21.23 43.33 25.09
53.71 18.43 38.21 21.88
47.99 20.87 60.04 28.04
WAL
Lower trapezius Serratus anterior
Values are expressed as mean (SD). a WAL: Wall facing arm lift. b PAL: Prone arm lift. c BRAL: Backward rocking arm lift. d BRDAL: Backward rocking diagonal arm lift.
PAL
BRAL
F
P
26.46 10.39
0.000 0.000
d
BRDAL
63.50 23.92 43.38 22.36
S.-m. Ha et al. / Physical Therapy in Sport 13 (2012) 227e232
* *
* 70 60
%MVIC
50 40 30 20 10
Exercise Type
R DA L B
R AL B
PA L
W
A
L
0
Fig. 3. Comparison of the serratus anterior muscle activity among four different exercises.
thoracic spine could be a possible explanation why the LT muscle activity was greater in BRDAL than in PAL. The thoracic spine will flex more in the BRDAL position compared to PAL. A flexed thoracic spine may induce scapula anterior tilting. Kebaetse et al. (1999) reported that a slouched posture decreased scapular posterior tilting during arm movements. The BRDAL position will be a more challenging position to tilt the scapular posteriorly. Therefore, it is likely that LT muscle activity was greater in the BRDAL position, compared to PAL. The SA muscle activity elicited by exercise in the BRAL position was significantly greater than that elicited by the other positions. For the SA, the BRAL exercise was performed with 180 shoulder abduction, whereas the other exercises were performed with 145 shoulder abduction. Several exercises have been used to activate SA muscles. SA muscle exercises using resistance, weights, or bodyweight are forward punch, push-up plus, and closed chain scapular protraction (Burkhart, Morgan, & Kibler, 2000; Hintermeister, Lange, Schultheis, Bey, & Hawkins, 1998; Moseley et al., 1992). Self-exercises with no external weight are the open-chain scapular protraction exercise, wall slide exercise, and scapular plane elevation (Burkhart et al., 2000; Hardwick et al., 2006; Ludewig et al., 1996). Several studies demonstrated that the maximum EMG activity in the SA muscle was shown during shoulder flexion or abduction exercise from 120 to 150 (Ekstrom et al., 2003; Hammer, 2006; Inman, Saunders, & Abbott, 1944; McClure et al., 2004; McMahon et al., 1996; Moseley et al., 1992). However, our results were not consistent with previous findings. Hammer (2006) and Sahrmann (2002) stated that SPT increased sharply at the end of shoulder abducted position. Bagg and Forrest (1986) reported that SA muscle activity increased continuously until maximal abduction. BRAL exercise was performed at the end-range of shoulder abduction (compared to the other three exercises), which simulates to maximal SPT (McClure et al., 2004), and facilitates activation of SA. Additionally, BRAL position has shortened range of SA muscle, which produced maximal muscle activity, compared to other exercise positions (Lunnen, Yack, & LeVeau, 1981). Furthermore, the BRAL position elicits less muscle activity in the LT because of fiber orientation (Ekstrom et al., 2003). Thus, the SA may require greater activation to produce maximal SPT in the BRAL position than in the other positions. The EMG activity of the SA was not significantly different among the WAT, PAL, and BRDAL exercise positions.
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Previous studies have shown that spine stabilization activates the target limb muscle, but also prevents unwanted motion and muscle activation (Cynn, Oh, Kwon, & Yi, 2006; Oh, Cynn, Won, Kwon, & Yi, 2007; Sahrmann, 2010). Some studies have investigated the effects of spine stabilization during lower extremity movement (Cynn et al., 2006; Oh et al., 2007); however, no study has assessed the effect of spine stabilization on the upper extremities. Stabilization of the cervical spine by pushing the forehead on the dorsum of hand and prevention of thoracic and lumbar extension using the backward rocking position may enhance the trunk stability. Isolated contraction of LT in BRDAL and SA in BRAL by stabilization of the spine could be a possible explanation for increasing muscle activity. We did not directly measure spine motion during the four arm-lifting SPT exercises; however, we postulate that stabilization of the spine in backward rocking position may have contributed to the increase in the muscle activity observed in the LT and SA muscles. Our study has several limitations. First, we did not measure the SPT during each arm lift exercise because it is difficult to collect kinematic data on SPT at the end-range. Further studies are necessary to determine correlation between the amount of SPT and other end-range exercises for the scapular. Second, the generalization of the study is limited because we recruited only young healthy subjects; thus, future studies are necessary to determine whether the present findings can be generalized to a symptomatic population. If patients are not able to perform end-range exercises, therapists can assist holding their shoulder at end-range. Furthermore, longitudinal studies are needed to assess the long-term effect of the backward-rocking exercises (BRAL and BRDAL) on selective activation of the LT and SA muscles. 5. Conclusions The present study measured EMG activity in the LT and SA muscles during different arm-lifting SPT exercises. LT muscle activity during BRDAL was significantly greater than that during the other exercises, whereas SA muscle activity during BRAL was significantly greater than during the other exercises. Clinicians can use these results to develop SPT exercises that specifically activate the LT or SA muscles. Conflict of Interest None declared. Ethical Approval This study was approved by the Yonsei University Wonju Campus Human Studies Committee. Funding None declared. References Arlotta, M., LoVasco, G., & McLean, L. (2011). Selective recruitment of the lower fibers of the trapezius muscle. Journal of Electromyography & Kinesiology, 21, 403e410. Bagg, S. D., & Forrest, W. J. (1986). Electromyographic study of the scapular rotators during arm abduction in the scapular plane. American Journal of Physical Medicine & Rehabilitation, 65, 111e124. Ballantyne, B. T., O’Hare, S. J., Paschall, J. L., Pavia-Smith, M. M., Pitz, A. M., Gillon, J. F., et al. (1993). Electromyographic activity of selected shoulder muscle in commonly used therapeutic exercises. Physical Therapy, 73, 668e682. Borsa, P. A., Timmons, M. K., & Sauers, E. L. (2003). Scapular-positioning patterns during humeral elevation in unimpaired shoulders. Journal of Athletic Training, 38, 12e17. Burkhart, S. S., Morgan, C. D., & Kibler, W. B. (2000). Shoulder injuries in the throwing athlete: the “dead arm” revisited. Clinical Sports Medicine, 19, 125e169. Clarkson, H. M. (2005). Joint motion and function assessment: A research-based practical guide. Philadelphia: Lippincott Williams & Wilkins.
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Cools, A. M., Witvrouw, E. E., Declercq, G. A., Danneels, L. A., & Cambier, D. C. (2003). Scapular muscle recruitment patterns: trapezius muscle latency with and without impingement symptoms. The American Journal of Sports Medicine, 31, 542e549. Cram, J. R., Kasman, G. S., & Holtz, J. (1998). Introduction to surface electromyography. Gaithersburg: Aspen Pub. Cynn, H. S., Oh, J. S., Kwon, O. Y., & Yi, C. H. (2006). Effects of lumbar stabilization using a pressure biofeedback unit on muscle activity and lateral pelvic tilt during hip abduction in sidelying. Archives of Physical Medicine and Rehabilitation, 87, 1454e1458. Decker, M. J., Hintermeister, R. A., Faber, K. J., & Hawkins, R. J. (1999). Serratus anterior muscle activity during selected rehabilitation exercises. The American Journal of Sports Medicine, 27, 784e791. De Mey, K., Cagnie, B., Danneels, L. A., Cools, A. M., & Van de Velde, A. (2009). Trapezius muscle timing during selected shoulder rehabilitation exercises. Journal of Orthopaedic & Sports Physical Therapy, 39, 743e752. De Oliveira, A. S., De Morais Carvalho, M., & De Brum, D. P. (2008). Activation of the shoulder and arm muscles during axial load exercises on a stable base of support and on a medicine ball. Journal of Electromyography & Kinesiology, 18, 472e479. Ebaugh, D. D., McClure, P. W., & Karduna, A. R. (2005). Three-dimensional scapulothoracic motion during active and passive arm elevation. Clinical Biomechanics, 2005, 700e709. Ekstrom, R. A., Donatelli, R. A., & Soderberg, G. L. (2003). Surface electromyographic analysis of exercises for the trapezius and serratus anterior muscles. Journal of Orthopaedic & Sports Physical Therapy, 33, 247e258. Ekstrom, R. A., Soderberg, G. L., & Donatelli, R. A. (2005). Normalization procedures using maximum voluntary isometric contractions for the serratus anterior and trapezius muscles during surface EMG analysis. Journal of Electromyography & Kinesiology, 15, 418e428. Escamilla, R. F., Yamashiro, K., Paulos, L., & Andrews, J. R. (2009). Shoulder muscle activity and function in common shoulder rehabilitation exercises. Sports Medicine, 39, 663e685. Hammer, W. I. (2006). Friction massage; from functional soft tissue examination and treatment by manual methods (3rd ed.). Gaithersberg: Aspen. Hardwick, D. H., Beebe, J. A., McDonnell, M. K., & Lang, C. E. (2006). A comparison of serratus anterior muscle activation during a wall slide exercise and other traditional exercises. Journal of Orthopaedic & Sports Physical Therapy, 36, 903e910. Hintermeister, R. A., Lange, G. W., Schultheis, J. M., Bey, M. J., & Hawkins, R. J. (1998). Electromyographic activity and applied load during shoulder rehabilitation exercises using elastic resistance. American Journal of Sports Medicine, 26, 210e220. Inman, V. T., Saunders, J. B., & Abbott, L. C. (1944). Observations on the function of the shoulder joint. Journal of Shoulder and Elbow Surgery, 26, 1e30. Kebaetse, M., McClure, P., & Pratt, N. A. (1999). Thoracic position effect on shoulder range of motion, strength, and three-dimensional scapular kinematics. Archives of Physical Medicine and Rehabilitation, 80, 945e950. Kendall, F. P., & McCreary, E. K. (2005). Muscles: Testing and function (5th ed.). Baltimore, MD: Williams & Wilkins. Kibler, W. B. (1998). The role of the scapula in athletic shoulder function. The American Journal of Sports Medicine, 26, 325e337. Kibler, W. B., & McMullen, J. (2003). Scapular dyskinesis and its relation to shoulder pain. Journal of the American Academy of Orthopaedic Surgeons, 11, 142e151. Kibler, W. B., Sciascia, A. D., Uhl, T. L., Tambay, N., & Cunningham, T. (2008). Electromyographic analysis of specific exercises for scapular control in early phases of shoulder rehabilitation. The American Journal of Sports Medicine, 36, 1789e1798. Lehman, G. J., MacMillan, B., MacIntyre, I., Chivers, M., & Fluter, M. (2006). Shoulder muscle EMG activity during push up variations on and off a Swiss ball. Dynamic Medicine, 9, 7. Lewis, J. S., Wright, C., & Green, A. (2005). Subacromial impingement syndrome: the effect of changing posture on shoulder range of movement. Journal of Orthopaedic & Sports Physical Therapy, 35, 72e87. Ludewig, P. M., & Cook, T. M. (2000). Alterations in shoulder kinematics and associated muscle activity in people with symptoms of shoulder impingement. Physical Therapy, 80, 276e291. Ludewig, P. M., Cook, T. M., & Nawoczenski, D. A. (1996). Three-dimensional scapular orientation and muscle activity at selected positions of humeral elevation. Journal of Orthopaedic & Sports Physical Therapy, 24, 57e65.
Lukasiewicz, A. C., McClure, P., & Michener, L. (1999). Comparison of 3-dimensional scapular position and orientation between subjects with and without shoulder impingement. Journal of Orthopaedic & Sports Physical Therapy, 29, 574e583. Lunnen, J. D., Yack, J., & LeVeau, B. F. (1981). Relationship between muscle length, muscle activity, and torque of the hamstring muscles. Physical Therapy, 61, 190e195. McClure, P. W., Bialker, J., Neff, N., Williams, G., & Karduna, A. (2004). Shoulder function and 3-dimensional kinematics in people with shoulder impingement syndrome before and after a 6-week exercise program. Physical Therapy, 84, 832e848. McMahon, P. J., Jobe, F. W., Pink, M. M., Brault, J. R., & Perry, J. (1996). Comparative electromyographic analysis of shoulder muscles during planar motions: anterior glenohumeral instability versus normal. Journal of Shoulder and Elbow Surgery, 5, 118e123. McQuade, K. J., Dawson, J., & Smidt, G. L. (1998). Scapulothoracic muscle fatigue associated with alterations in scapulohumeral rhythm kinematics during maximum resistive shoulder elevation. Journal of Orthopaedic & Sports Physical Therapy, 28, 74e80. Michener, L. A., & Leggin, B. G. (2001). A review of self-report scales for the assessment of functional limitation and disability of the shoulder. Journal of Hand Therapy, 14, 68e76. Michener, L. A., McClure, P. W., & Karduna, A. R. (2003). Anatomical and biomechanical mechanisms of subacromial impingement syndrome. Clinical Biomechanics, (Bristol, Avon), 18, 369e379. Moseley, J. B., Jobe, F. W., Pink, M., Perry, J., & Tibone, J. (1992). EMG analysis of the scapular muscles during a shoulder rehabilitation program. The American Journal of Sports Medicine, 20,128e20,134. Oh, J. S., Cynn, H. S., Won, J. H., Kwon, O. Y., & Yi, C. H. (2007). Effects of performing an abdominal drawing-in maneuver during prone hip extension exercises on hip and back extensor muscle activity and amount of anterior pelvic tilt. Journal of Orthopaedic & Sports Physical Therapy, 37, 320e324. Oyama, S., Myers, J. B., Wassinger, C. A., & Lephart, S. M. (2010). Three-dimensional scapular and clavicular kinematics and scapular muscle activity during retraction exercises. Journal of Orthopaedic & Sports Physical Therapy, 40, 169e179. Phil, P., Clare, F., & Robert, L. (2010). Assessment and treatment of muscle imbalance: The janda approach. United States: Human Kinetics, Inc. Pontillo, M., Orishimo, K. F., Kremenic, I. J., McHugh, M. P., Mullaney, M. J., & Tyler, T. F. (2007). Shoulder musculature activity and stabilization during upper extremity weight-bearing activities. North American Journal of Sports Physical Therapy, 2, 90e96. Sahrmann, S. (2002). Diagnosis and treatment of movement impairment syndrome. St. Louis, Missouri: Mosby. Sahrmann, S. (2010). Movement system impairment syndromes of the extremities, cervical and thoracic spines. St. Louis, Missouri: Mosby. Smith, J., Dahm, D. L., Kaufman, K. R., Boon, A. J., Laskowski, E. R., Kotajarvi, B. R., et al. (2006). Electromyographic activity in the immobilized shoulder girdle musculature during scapulothoracic exercises. Archives of Physical Medicine and Rehabilitation, 87, 923e927. Solem-Bertoft, E., Thuomas, K. A., & Westerberg, C. E. (1993). The influence of scapular retraction and protraction on the width of the subacromial space: an MRI study. Clinical Orthopaedics and Related Research, 296, 99e103. Townsend, H., Jobe, F. W., Pink, M., & Perry, J. (1991). Electromyographic analysis of the glenohumeral muscles during a baseball rehabilitation program. The American Journal of Sports Medicine, 19, 264e272. Vera-Garcia, F. J., Moreside, J. M., & McGill, S. M. (2010). MVC techniques to normalize trunk muscle EMG in healthy women. Journal of Electromyography & Kinesiology, 20, 10e16. Vezina, M. J., & Hubley-Kozey, C. L. (2000). Muscle activation in therapeutic exercises to improve trunk stability. Archives of Physical Medicine and Rehabilitation, 81, 1370e1979. Warner, J. J., Micheli, L. J., Arslanian, L. E., Kennedy, J., & Kennedy, R. (1992). Scapulothoracic motion in normal shoulders and shoulders with glenohumeral instability and impingement syndrome: a study using Moire topographic analysis. Clinical Orthopaedics and Related Research, 285, 191e199. Wuelker, N., Wirth, C. J., Plitz, W., & Roetman, B. (1995). A dynamic shoulder model: reliability testing and muscle force study. Journal of Biomechanics, 28, 489e499. Yoshizaki, K., Hamada, J., Tamai, K., Sahara, R., Fujiwara, T., & Fujimoto, T. (2009). Analysis of the scapulohumeral rhythm and electromyography of the shoulder muscles during elevation and lowering: comparison of dominant and nondominant shoulders. Journal of Shoulder and Elbow Surgery, 18, 756e763.
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Physical Therapy in Sport journal homepage: www.elsevier.com/ptsp
Original research
Comparison of electromyographic activity of the lower trapezius and serratus anterior muscle in different arm-lifting scapular posterior tilt exercises Sung-min Ha a, Oh-yun Kwon b, *, Heon-seock Cynn c, Won-hwee Lee a, Kyue-nam Park a, Si-hyun Kim a, Do-young Jung d a
Department of Rehabilitation Therapy, Graduate School of Yonsei University, Wonju, Republic of Korea Department of Physical Therapy, College of Health Science, Laboratory of Kinetic Ergocise Based on Movement Analysis, Yonsei University, 234 Maeji-ri, Heungeop-myeon, Wonju, Kangwon-do 220-710, Republic of Korea c Department of Physical Therapy, College of Health Science, Yonsei University, Wonju, Republic of Korea d Department of Physical Therapy, College of Tourism & Health, Joongbu University, 101 Daehak-ro, Chubu-myeon, Geumsan-gun, Chungnam, Republic of Korea b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 February 2011 Received in revised form 21 September 2011 Accepted 9 November 2011
Objective: To determine the most effective exercise to specifically activate the scapular posterior tilting muscles by comparing muscle activity generated by different exercises (wall facing arm lift, prone arm lift, backward rocking arm lift, backward rocking diagonal arm lift). Design: Repeated-measure within-subject intervention. Participants: The subjects were 20 healthy young men and women. Main outcome measures: Lower trapezius (LT) and serratus anterior (SA) muscle activity was measured when subjects performed the four exercises. Results: Muscle activity was significantly different among the four exercise positions (p < 0.05). The backward rocking diagonal arm lift elicited significantly greater activity in the LT muscle than did the other exercises (p < 0.05). The backward rocking arm lift showed significantly more activity in the SA muscle than did the other exercises (p < 0.05). Conclusions: Clinicians can use these results to develop scapular posterior tilting exercises that specifically activate the target muscle. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: Arm lift Lower trapezius Scapular posterior tilting Serratus anterior
1. Introduction When elevating the arm overhead, the normal scapula undergoes a pattern of upward rotation (45e60 ), external rotation (15e35 ), and posterior tilting (20e40 ) (Escamilla, Yamashiro, Paulos, & Andrews, 2009; Ludewig, Cook, & Nawoczenski, 1996). To complete, 180 of humeral elevation, the scapula should depress, slightly adduct, and tilt posteriorly at the end-range of scapular upward rotation (Sahrmann, 2002). Scapular posterior tilt (SPT) is the movement of the coracoid process in a posterior and cranial direction while the inferior angle of the scapula moves in an anterior and caudal direction (Clarkson, 2005). During arm elevation, SPT occurs about a medial-lateral axis of the scapula, with the
* Corresponding author. Tel.: þ82 33 760 2721; fax: þ82 33 760 2496. E-mail addresses: [email protected] (S.-m. Ha), [email protected] (O.-y. Kwon), [email protected] (H.-s. Cynn), [email protected] (W.-h. Lee), [email protected] (K.-n. Park), [email protected] (S.-h. Kim), ptsports@ hotmail.com (D.-y. Jung). 1466-853X/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ptsp.2011.11.002
inferior angle moving anteriorly (Michener, McClure, & Karduna, 2003), which occurs primarily after 90 and increases sharply at the end-range (Hammer, 2006). SPT may be important in allowing the humeral head and rotator cuff tendons to clear the anterior aspect of the acromion during arm elevation (Escamilla et al., 2009). In particular, athletes or workers involved in overhead activity with abnormal scapular movement at the extremes of humeral elevation are likely to develop shoulder conditions such as subacromial impingement (SI) and glenohumeral instability (Ludewig et al., 1996; McQuade, Dawson, & Smidt, 1998; Warner, Micheli, Arslanian, Kennedy, & Kennedy, 1992). Subjects with SI have approximately 10 less posterior tilt than asymptomatic subjects (Lukasiewicz, McClure, & Michener, 1999). Coordination of SPT muscles is important to prevent abnormal scapular movement and pain during elevation of the arm overhead (Solem-Bertoft, Thuomas, & Westerberg, 1993). The main muscles thought to facilitate SPT are the LT (lower trapezius) and SA (Serratus anterior) (Ebaugh, McClure, & Karduna,
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2005). These muscles are paired to form an important force couple that controls SPT, which is important for widening the subacromial space during overhead activities to prevent impingement of the subacromial tissues (Michener & Leggin, 2001; Solem-Bertoft et al., 1993). A change in the LT and SA muscle function influences SPT and is associated with poor shoulder function and chronic SI (Cools, Witvrouw, Declercq, Danneels, & Cambier, 2003; Kibler & McMullen, 2003). Furthermore, reduction in the force generation of the SPT muscles increases the potential for developing SI syndrome (Ludewig & Cook, 2000; Wuelker, Wirth, Plitz, & Roetman, 1995). Many studies have addressed strengthening exercises of the LT and SA muscle to treat shoulder dysfunction (Arlotta, LoVasco, & McLean, 2011; Ekstrom, Donatelli, & Soderberg, 2003; Hardwick, Beebe, McDonnell, & Lang, 2006; Pontillo, Orishimo, Kremenic, McHugh, Mullaney, & Tyler, 2007). SA muscle activity increases in a linear fashion with arm elevation (Kibler, Sciascia, Uhl, Tambay, & Cunningham, 2008; Ludewig et al., 1996). Conversely, LT muscle activity tends to be low at less than 90 of scaption, abduction, and flexion, and then increases exponentially from 90 to 180 (Hardwick et al., 2006; Smith et al., 2006). Ekstrom et al. (2003) reported that prone overhead arm raise in line with the LT muscle produced maximum activity in the LT muscle. Selective strengthening of the muscles that facilitate SPT is important for rehabilitation of scapular movement impairment; there are plenty of studies available to help clinicians develop effective programs to exercise these muscles (Decker, Hintermeister, Faber, & Hawkins, 1999; Ekstrom et al., 2003; Ekstrom, Soderberg, & Donatelli, 2005; Hardwick et al., 2006; Kibler, 1998; Oyama, Myers, Wassinger, & Lephart, 2010). Effective exercise positions are based on what is known of the functional anatomy and biomechanics of the shoulder complex, previous electromyography (EMG) studies, and clinical experience (Ballantyne et al., 1993). Recently, clinicians and researchers have focused on activation of the LT and SA muscles for normal scapular upward rotation at arm elevation angles above 90 (Decker et al., 1999; Ekstrom et al., 2003, 2005; Hardwick et al., 2006; Kibler, 1998). Representative exercises include the wall facing arm lift, scapular plane shoulder elevation, and overhead arm raise (Decker et al., 1999; Ekstrom et al., 2003; Hardwick et al., 2006; Townsend, Jobe, Pink, & Perry, 1991). Hardwick et al. (2006) reported that SA activity significantly increased with increasing humeral elevation angle (90 , 120 , and 140 ), with no significant differences between the wall slide (37.1e75.4% MVIC) and scapular plane shoulder elevation exercises (41.1e82.4% MVIC). Ekstrom et al. (2003) found the SA muscle activity was significantly higher in the scapular plane shoulder elevation exercises (96% MVIC) above 120 than below 80 , and the overhead arm raise in line with LT muscle fibers was the highest level of LT muscle activity (97% MVIC). Oyama et al. (2010) reported that LT activity (72% MVIC) was highest in 120 shoulder abduction with external rotation (thumb pointing toward ceiling) among 6 scapular retraction exercises. The stabilization of spine, posture of the thorax and shoulder abduction angle may affect SPT and upper extremity movement (Kebaetse, McClure, & Pratt 1999; Lewis, Wright, & Green, 2005; Sahrmann, 2010). To our knowledge, no reported study has quantified activity in the LT and SA muscles at the final stage of scapular upward rotation (i.e., during SPT) during different arm-lifting SPT exercises. The present study compared the muscle activity during the wall facing arm lift (WAL), prone arm lift (PAL), backward rocking arm lift (BRAL), and backward rocking diagonal arm lift (BRDAL) exercises to determine the most effective exercise for activating the LT and SA muscles. We hypothesized that activity of the LT and SA muscles would differ among the four arm-lifting SPT exercises.
2. Methods 2.1. Subjects Twenty healthy young subjects (10 men, 10 women) participated in this study (Table 1). The inclusion criteria were 1) the subject was able to comfortably perform full flexion in the sagittal plane, full abduction in the frontal plane, and full scaption in the scapular plane; 2) the pectoralis minor, levator scapulae, and rhomboid muscles were within the normal length using muscle length tests (Phil, Clare, & Robert, 2010; Sahrmann, 2002). The exclusion criteria were current shoulder pain or shoulder surgery and history of neurological, musculoskeletal, or cardiopulmonary disease that could interfere with shoulder motion in the testing positions. The principal investigator explained the procedure to the subjects in detail prior to the experiment and all subjects signed an informed consent form. This study was approved by the Yonsei University Wonju Campus Human Studies Committee. 2.2. Instrumentation EMG data were collected using a Noraxon TeleMyo 2400T and analyzed using MyoResearch Master Edition 1.06 XP software (Noraxon, Scottsdale, AZ, USA). The electrode sites was shaved and cleaned with rubbing alcohol. Surface electrode pairs were positioned at an interelectrode distance of 2 cm. The reference electrode was placed on the ipsilateral clavicle. EMG data were collected for the LT muscle (placed at an oblique vertical angle with one electrode superior and one inferior to a point 5 cm inferomedial from the root of the spine of the scapula) and the SA muscle (placed vertically along the mid-axillary line at rib levels 6e8) (Cram, Kasman, & Holtz, 1998). The sampling rate was 1000 Hz. A bandpass filter between 20 and 300 Hz was used. EMG data were processed into the root-mean-square (RMS) value, which was calculated from 50-ms data points of windows. 2.3. Procedures The dominant arm (the preferred arm when performing eating and writing tasks) was used in all tests (Yoshizaki, Hamada, Tamai, Sahara, Fujiwara, & Fujimoto, 2009). All subjects reported the right arm as their dominant arm. EMG activity in the LT and SA muscles was tested during four different exercises. A target bar was used to control the angle of shoulder flexion in each exercise. The target bar distance was determined by a vertical line from the wall to the subject’s earlobe in the WAL exercise position. The target bar was placed at this same distance from the surface of the therapeutic table in the PAL, BRAL, and BRDAL exercises. These exercises distinguished by exercise position (standing, prone, and backward rocking), and shoulder abduction angle (180 , and 145 ). 2.4. Wall facing arm lift (WAL) Hardwick et al. (2006) and Sahrmann (2002) described the wall slide exercise. The subject was required to stand facing the wall and contact it from nose to knees with feet shoulder-width apart. In the starting position, the ulnar border of the forearms and medial side Table 1 Descriptive data for participants in this study (n ¼ 20). Variable
ALL
Male (n ¼ 10)
Female (n ¼ 10)
Age (y) Height (cm) Mass (kg)
23.1 1.8 168.5 6.3 58.4 6.8
23.6 2.2 173.7 4.2 64.0 4.5
22.6 1.3 163.2 2.5 52.8 2.6
Values are expressed as mean (SD).
S.-m. Ha et al. / Physical Therapy in Sport 13 (2012) 227e232
of the humerus were in contact with the wall, and shoulder abducted 90 with elbow flexed 90 . The subjects were instructed to slide their arms up the wall. The sliding movement was ended when the shoulder reached 145 of abduction. The subject was then instructed to lift both hands with elbows extended until the radial border of the wrist slightly touched without pushing the target bar and maintained the arm position (Fig. 1A). 2.5. Prone arm lift (PAL) The subject was placed in the prone position. Using a goniometer, the humerus was aligned diagonally overhead with shoulder abduction of 145 and the forearm was in the neutral position. The subjects were asked to place the non-dominant hand under the forehead and push slightly on the forehead with the dorsum of their hand to stabilize the neck and thoracic spine. The subject was then instructed to lift the dominant arm with elbow extended until the radial border of the wrist slightly touched without pushing the target bar and maintained the arm position, which was placed at the same distance used in the WAL exercise (Ekstrom et al., 2003) (Fig. 1B). 2.6. Backward rocking arm lift (BRAL) We invented the backward rocking arm lift exercise. Initially, the subjects were placed in the quadruped position and instructed to rock backward slowly until the buttocks touched both heels. The subjects were asked to place the non-dominant hand under the forehead and push slightly on the forehead with the dorsum of the hand to stabilize the neck and thoracic spine. The principal investigator abducted the subject’s dominant shoulder to 180 using a goniometer. The subject was then instructed to lift the dominant arm until the radial border of the wrist slightly touched without pushing the target bar and maintained the arm position, which was located in a predetermined position (Fig. 1C). 2.7. Backward rocking diagonal arm lift (BRDAL) The subjects were placed in the quadruped position and instructed to rock backward slowly, and the head was positioned as in the BRAL exercise. The shoulder was abducted to 145 by the
229
principal investigator and the subject was instructed to lift the dominant arm with the elbow extended until the radial border of the wrist slightly touched without pushing the target bar and maintained the arm position, which was located in the predetermined position (Fig. 1D). Subjects were familiarized with the four arm-lifting SPT exercises during a 30 min period prior to testing. During the familiarization period, the principal investigator instructed the subjects to move their dominant arm until the radial border of the wrist touched the target bar, which was located in a predetermined position for each exercise. The familiarization period was completed when the subject was able to maintain the four exercise positions for 5 s. All of the subjects were comfortable after the familiarization period, and none reported fatigue. A 15 min rest period was allowed after the familiarization period before data collection began.
2.8. Data collection and processing The order of testing was randomized using the random number generator in Microsoft Excel (Microsoft Corp., Redmond, WA, USA). The EMG data were normalized by calculating the mean RMS of three trials of maximal voluntary isometric contraction (MVIC) for each muscle. We used the manual muscle testing positions recommended by Kendall and McCreary (2005) for measuring MVIC. LT muscle activity was tested in the prone position; the subject’s arm was placed diagonally overhead, in line with the lower fibers of the trapezius muscle during external rotation, while resistance was applied distal to the elbow. The SA muscle was tested while the subject was seated on a treatment table with no back support. The shoulder was internally rotated and abducted to 125 in the scapular plane, while resistance was applied proximal to the subject’s elbow by the principal investigator. Each contraction was held for 6 s with maximal effort against manual resistance. The first and last second of the EMG data from each MVIC trial were discarded, and the remaining 4 s of data were used (De Oliveira, De Morais Carvalho, & De Brum, 2008; Vezina & Hubley-Kozey, 2000). Three repetitions of each test were performed, with a 2 min rest interval between repetitions to minimize muscle fatigue (Vera-Garcia, Moreside, & McGill, 2010). The mean MVIC value of the three trials was calculated.
Fig. 1. Type of exercise (A: Wall facing arm lift, B: Prone arm lift, C: Backward rocking arm lift, D: Backward rocking diagonal arm lift).
S.-m. Ha et al. / Physical Therapy in Sport 13 (2012) 227e232
*
Each isometric arm-lifting exercise was performed for 6 s; the first and last second of each exercise trial were discarded, and the remaining 4 s of EMG data were used (De Oliveira et al., 2008; Vezina, & Hubley-Kozey, 2000). The mean of three trials for each arm-lifting exercise was analyzed. The participants were allowed to rest for 2 min between trials, and 3 min between the different exercises positions (De Mey, Cagnie, Danneels, Cools, & Van de Velde, 2009; Lehman, MacMillan, MacIntyre, Chivers, & Fluter, 2006). The data for each trial were expressed as a percentage of the calculated mean RMS of the MVIC (% MVIC), and the mean % MVIC of the three trials was used in the analysis.
*
* 70
*
*
60
%MVIC
50 40 30 20
2.9. Data analysis and statistics
10
B
B
RD
A
L
R AL
L
L
0
W A
A one-way repeated-measure analysis of variance (ANOVA) was used to test for differences in LT and SA muscle activities among the four arm-lifting SPT exercises. Significant main effects were followed up using the Bonferroni post-hoc test. The Statistical Package for the Social Sciences version 12 (SPSS Inc., Chicago, IL, USA) was used to conduct the statistical tests, and p-values <0.05 were deemed statistically significant.
PA
230
Exercise Type Fig. 2. Comparison of the lower trapezius muscle activity among four different exercises.
3. Results The normalized EMG data and the results of the statistical analyses are shown in Table 2. LT muscle activity was significantly higher when performing the BRDAL compared to the other exercises (Fig. 2). The LT muscle activity is shown in Table 2. It increased in the order of WAL < BRAL < PAL < BRDAL (p < 0.05) (Fig. 2). LT muscle activity was significantly lower during the WAL exercise than during the other exercises (p < 0.05). LT muscle activity did not differ significantly different between the PAL and BRAL exercises. SA muscle activity was significantly greater when performing the BRAL exercise than during the other exercises (p < 0.05) (Fig. 3). SA muscle activity did not differ significantly among the WAL, PAL, and BRDAL exercises. 4. Discussion We investigated muscle activity in the LT and SA muscles during four different arm-lifting SPT exercises. Sufficient upward rotation and posterior tilting of the scapula are essential components for throwing and overhead activities (Borsa, Timmons, & Sauers, 2003; Hammer, 2006; McClure, Bialker, Neff, Williams, & Karduna, 2004). We believe that our study is the first to investigate activity of the LT and SA muscles at the end-range of scapular upward rotation during different arm-lifting SPT exercises. For the LT, our results showed that the LT muscle activity was significantly greater during the BRDAL exercise than during the PAL, BRAL, or WAL exercises (p < 0.05). Previous studies using Kendall’s instructions (Kendall, & McCreary, 2005) for positioning the LT during muscle testing found that the “diagonal overhead” arm
raised in line with the lower part of the trapezius in the prone position produced the maximum mean EMG activity (97% MVIC) in this muscle (Ekstrom et al., 2003). Oyama et al. (2010) reported that LT activity (72% MVIC) was highest in 120 shoulder abduction with external rotation (thumb pointing toward ceiling) among 6 scapular retraction exercises. The results of our study are similar to those of previous studies showing that LT muscle activity is highest when the shoulder is abducted to 145 . Moseley, Jobe, Pink, Perry, and Tibone (1992) reported that, of the 16 exercises tested, the prone rowing exercise with shoulder abduction below 90 was the most effective in activating the LT muscle. Prone external rotation at 90 abduction has been reported to increase LT muscle activity significantly more than the empty can exercise (Ballantyne et al., 1993). It is difficult to compare the results of our study directly with those of previous studies because of the different exercise positions and protocols. We found that BRDAL elicited a higher level of LT muscle activity (63.49 %MVIC) than did the other exercises (PAL: 53.71 18.43% MVIC, BRAL: 47.99 20.87% MVIC, WAL: 25.88 21.23% MVIC), whereas the WAL position elicited the lowest level of LT muscle activity. The BRDAL, PAL, and BRAL exercises were performed in antigravity positions, which may explain why the WAL position elicited the least LT muscle activity of the four arm-lifting SPT exercises. In the present study, LT muscle activity elicited by BRAL was less than that elicited by BRDAL and PAL. McMahon, Jobe, Pink, Brault, and Perry (1996) reported that LT muscle activity was greater at 145 shoulder abduction than at 180 in the prone position. The BRAL exercise was performed at 180 shoulder abduction in the present study. Unlike the WAL and PAL exercises, the BRDAL exercise was performed with the neck and trunk stabilized by the backward rocking position. Position of
Table 2 Mean (SD) EMG activation expressed as a percentage of maximal voluntary isometric contraction for each exercise. Muscle
Exercise a
b
c
25.88 21.23 43.33 25.09
53.71 18.43 38.21 21.88
47.99 20.87 60.04 28.04
WAL
Lower trapezius Serratus anterior
Values are expressed as mean (SD). a WAL: Wall facing arm lift. b PAL: Prone arm lift. c BRAL: Backward rocking arm lift. d BRDAL: Backward rocking diagonal arm lift.
PAL
BRAL
F
P
26.46 10.39
0.000 0.000
d
BRDAL
63.50 23.92 43.38 22.36
S.-m. Ha et al. / Physical Therapy in Sport 13 (2012) 227e232
* *
* 70 60
%MVIC
50 40 30 20 10
Exercise Type
R DA L B
R AL B
PA L
W
A
L
0
Fig. 3. Comparison of the serratus anterior muscle activity among four different exercises.
thoracic spine could be a possible explanation why the LT muscle activity was greater in BRDAL than in PAL. The thoracic spine will flex more in the BRDAL position compared to PAL. A flexed thoracic spine may induce scapula anterior tilting. Kebaetse et al. (1999) reported that a slouched posture decreased scapular posterior tilting during arm movements. The BRDAL position will be a more challenging position to tilt the scapular posteriorly. Therefore, it is likely that LT muscle activity was greater in the BRDAL position, compared to PAL. The SA muscle activity elicited by exercise in the BRAL position was significantly greater than that elicited by the other positions. For the SA, the BRAL exercise was performed with 180 shoulder abduction, whereas the other exercises were performed with 145 shoulder abduction. Several exercises have been used to activate SA muscles. SA muscle exercises using resistance, weights, or bodyweight are forward punch, push-up plus, and closed chain scapular protraction (Burkhart, Morgan, & Kibler, 2000; Hintermeister, Lange, Schultheis, Bey, & Hawkins, 1998; Moseley et al., 1992). Self-exercises with no external weight are the open-chain scapular protraction exercise, wall slide exercise, and scapular plane elevation (Burkhart et al., 2000; Hardwick et al., 2006; Ludewig et al., 1996). Several studies demonstrated that the maximum EMG activity in the SA muscle was shown during shoulder flexion or abduction exercise from 120 to 150 (Ekstrom et al., 2003; Hammer, 2006; Inman, Saunders, & Abbott, 1944; McClure et al., 2004; McMahon et al., 1996; Moseley et al., 1992). However, our results were not consistent with previous findings. Hammer (2006) and Sahrmann (2002) stated that SPT increased sharply at the end of shoulder abducted position. Bagg and Forrest (1986) reported that SA muscle activity increased continuously until maximal abduction. BRAL exercise was performed at the end-range of shoulder abduction (compared to the other three exercises), which simulates to maximal SPT (McClure et al., 2004), and facilitates activation of SA. Additionally, BRAL position has shortened range of SA muscle, which produced maximal muscle activity, compared to other exercise positions (Lunnen, Yack, & LeVeau, 1981). Furthermore, the BRAL position elicits less muscle activity in the LT because of fiber orientation (Ekstrom et al., 2003). Thus, the SA may require greater activation to produce maximal SPT in the BRAL position than in the other positions. The EMG activity of the SA was not significantly different among the WAT, PAL, and BRDAL exercise positions.
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Previous studies have shown that spine stabilization activates the target limb muscle, but also prevents unwanted motion and muscle activation (Cynn, Oh, Kwon, & Yi, 2006; Oh, Cynn, Won, Kwon, & Yi, 2007; Sahrmann, 2010). Some studies have investigated the effects of spine stabilization during lower extremity movement (Cynn et al., 2006; Oh et al., 2007); however, no study has assessed the effect of spine stabilization on the upper extremities. Stabilization of the cervical spine by pushing the forehead on the dorsum of hand and prevention of thoracic and lumbar extension using the backward rocking position may enhance the trunk stability. Isolated contraction of LT in BRDAL and SA in BRAL by stabilization of the spine could be a possible explanation for increasing muscle activity. We did not directly measure spine motion during the four arm-lifting SPT exercises; however, we postulate that stabilization of the spine in backward rocking position may have contributed to the increase in the muscle activity observed in the LT and SA muscles. Our study has several limitations. First, we did not measure the SPT during each arm lift exercise because it is difficult to collect kinematic data on SPT at the end-range. Further studies are necessary to determine correlation between the amount of SPT and other end-range exercises for the scapular. Second, the generalization of the study is limited because we recruited only young healthy subjects; thus, future studies are necessary to determine whether the present findings can be generalized to a symptomatic population. If patients are not able to perform end-range exercises, therapists can assist holding their shoulder at end-range. Furthermore, longitudinal studies are needed to assess the long-term effect of the backward-rocking exercises (BRAL and BRDAL) on selective activation of the LT and SA muscles. 5. Conclusions The present study measured EMG activity in the LT and SA muscles during different arm-lifting SPT exercises. LT muscle activity during BRDAL was significantly greater than that during the other exercises, whereas SA muscle activity during BRAL was significantly greater than during the other exercises. Clinicians can use these results to develop SPT exercises that specifically activate the LT or SA muscles. Conflict of Interest None declared. Ethical Approval This study was approved by the Yonsei University Wonju Campus Human Studies Committee. Funding None declared. References Arlotta, M., LoVasco, G., & McLean, L. (2011). Selective recruitment of the lower fibers of the trapezius muscle. Journal of Electromyography & Kinesiology, 21, 403e410. Bagg, S. D., & Forrest, W. J. (1986). Electromyographic study of the scapular rotators during arm abduction in the scapular plane. American Journal of Physical Medicine & Rehabilitation, 65, 111e124. Ballantyne, B. T., O’Hare, S. J., Paschall, J. L., Pavia-Smith, M. M., Pitz, A. M., Gillon, J. F., et al. (1993). Electromyographic activity of selected shoulder muscle in commonly used therapeutic exercises. Physical Therapy, 73, 668e682. Borsa, P. A., Timmons, M. K., & Sauers, E. L. (2003). Scapular-positioning patterns during humeral elevation in unimpaired shoulders. Journal of Athletic Training, 38, 12e17. Burkhart, S. S., Morgan, C. D., & Kibler, W. B. (2000). Shoulder injuries in the throwing athlete: the “dead arm” revisited. Clinical Sports Medicine, 19, 125e169. Clarkson, H. M. (2005). Joint motion and function assessment: A research-based practical guide. Philadelphia: Lippincott Williams & Wilkins.
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