Original researchComparison of scapular posterior tilting exercise alone and scapular posterior tilting exercise after pectoralis minor stretching on scapular alignment and scapular upward rotators activity in subjects with short pectoralis minor
Introduction
Scapular dyskinesis is considered to be a factor in the development of shoulder pathologies, such as subacromial impingement syndrome (Atalar, 2009, Ludewig and Braman, 2011, Ludewig and Cook, 2000, Ludewig et al., 1996, Lukasiewicz et al., 1999, McQuade et al., 1998, Su et al., 2004, Warner et al., 1992). The most common contributing mechanisms of scapular dyskinesis may be soft tissues alterations including inflexibility or imbalance of the periscapular muscles (Kibler, Sciascia, & Wilkes, 2012). Especially, shortness of the pectoralis minor muscle (PM) may be a main cause of scapular dyskinesis (Ludewig and Cook, 2000, McClure et al., 2012). Reduced PM flexibility creates scapular anterior tilting and protraction as a result of the PM pulling on the coracoid and inflexibility of the muscle limits scapular external rotation, upward rotation, and posterior tilting (Borstad and Ludewig, 2005, Muraki et al., 2009).
The main periscapular muscles involved in increasing scapular upward rotation and posterior tilting are the upper trapezius (UT), lower trapezius (LT), and serratus anterior (SA) (Ebaugh, McClure, & Karduna, 2006). LT maintains scapular upward rotation and SA stabilizes the medial border of the scapula against the thorax after 90° arm elevation (Kibler et al., 2012). Middle trapezius is also important because it could stabilize the scapula to avoid excessive protraction during arm elevation. Among these periscapular muscles, LT and SA control scapular posterior tilting as well as scapular upward rotation; such tilting is important for widening the subacromial space during overhead activities to prevent impingement of the subacromial tissues (Cools et al., 2003, Kibler and McMullen, 2003, Michener and Leggin, 2001, Solem-Bertoft et al., 1993). A recent study reported that hyperactivity of the UT with decreased middle trapezius and LT muscle activity, as well as insufficient SA muscle activity, had been related to decreased scapular upward rotation and posterior tilt in patients with subacromial impingement (Ludewig & Braman, 2011). Thus, increasing the flexibility of PM and LT and SA activation might be important for the treatment of patients with subacromial impingement syndrome resulting from dyskinesis.
Many previous studies have examined the effectiveness of various exercises to increase the flexibility of PM and the activity of LT and SA, including stretching techniques of PM (Borstad and Ludewig, 2005, Borstad and Ludewig, 2006, Muraki et al., 2009, Roddey et al., 2002, Wang et al., 1999, Williams et al., 2013) and strengthening exercises focusing on the LT and SA muscles (Arlotta et al., 2011, Ekstrom et al., 2003, Ha et al., 2012, Hardwick et al., 2006, Pontillo et al., 2007). Of these various exercises, the self-stretching technique (Borstad & Ludewig, 2006) and gross stretching technique (Williams et al., 2013) resulted in significant increases in the length of PM compared to the other stretching techniques. However, in the present study, we used the modified gross stretching exercise to allow the investigator to better control the amount of applied overpressure to the glenohumeral joint and anterior shift of the humeral head and to avoid unwanted movement, such as elevation of the ribcage, during the stretching. In addition, many previous studies have investigated various exercises to determine the most effective exercise to elicit LT and SA strengthening (Arlotta et al., 2011, Ekstrom et al., 2003, Ha et al., 2012, Hardwick et al., 2006, Pontillo et al., 2007). The V raise exercise in the prone position might be the most efficient method to strengthen the LT for stabilizing the scapula on the thoracic wall. Ekstrom et al. (2003) reported that the “diagonal overhead” arm raised in line with the LT in the prone position produced the maximum mean electromyographic (EMG) activity (97.00% maximal voluntary isometric contraction [MVIC]) in this muscle because the muscles are in an antigravity position while in the prone position. Ha et al. (2012) reported that 145° shoulder abduction elicited significantly greater LT muscle activity. Many previous studies also reported that the maximum SA activity was observed during shoulder flexion and abduction exercise from 120° to 150° (Ekstrom et al., 2003, Hammer, 2006, Inman et al., 1944, McClure et al., 2004, McMahon et al., 1996, Moseley et al., 1992). Additionally, a previous study (Ha et al., 2012) demonstrated that the backward rocking position during the scapular posterior tilting exercise could maintain neck and trunk stability. For these reasons, this study utilized gross PM stretching to facilitate the flexibility of PM and 145° shoulder abduction with backward rocking to increase the activity of LT and SA.
Management of scapular dyskinesis necessitates scapular examination. To accurately assess scapular dyskinesis, previous investigators introduced three-dimensional wing computed tomography (Park, Hwang, & Oh, 2014). Despite the advantages offered by the three-dimensional dyskinesis method, however, it does not easily enable measurement mainly because it is too expensive and the equipment is excessively bulky. Given that clinicians could not use this approach, they typically employ Kibler's observational typing method, which was considered the gold standard in clinical examinations (Kibler and McMullen, 2003, Uhl et al., 2009). Nevertheless, even though Kibler's observational typing method is practical, the current study opted to measure scapular anterior tilting (scapular anterior tilting index) and the scapular upward rotation angle. This decision was based on the fact that observational typing (four types) has relatively low inter-rater reliability and cannot represent ratio-level data (Ellenbecker, Kibler, Bailie, Caplinger, Davies, & Riemann, 2012). Thus, the aforementioned measurement techniques were chosen in examining the changes that occurred directly after PM stretching.
In the presence of a short PM, LT and SA activity can be inhibited when the shoulder is elevated. PM stretching might be used to reduce muscle imbalance before exercises to activate LT and SA muscle activity for subjects with a short PM. Even if this technique might be helpful, no previous studies have investigated a strategy to increase the flexibility of PM and the activation of LT and SA in subjects with a short PM. To fill this gap, the present research compared the effects of scapular posterior tilting exercise alone (henceforth, SPT) and scapular posterior tilting exercise after PM stretching (henceforth, PM stretch + SPT) on the PM index (PMI), scapular anterior tilting index, scapular upward rotation angle, and scapular upward rotator activity (UT, LT, and SA) in subjects with a short PM. The hypothesis of this study was that the scapular anterior tilting index would be decreased and that the PMI, scapular upward rotation angle, UT, LT, and SA muscle activity would be increased in PM stretch + SPT for subjects with a short PM.
Section snippets
Subjects
G-power software provided power analyses. A sample size of 12 subjects was obtained from a pilot study of 10 subjects to achieve a power of 0.80 and an effect size of 0.79 (calculated by differences of mean and standard deviation [SD] from the pilot study), with an α level of 0.05. Asymptomatic subjects were recruited from the university. We recruited 25 subjects in the beginning of the study. Fifteen subjects with a short PM participated in this study (age = 22.07 ± 1.95 years,
PMI, scapular anterior tilting index, and scapular upward rotation angle
The PMI and the scapular upward rotation angle were significantly greater after PM stretch + SPT than SPT (p < 0.05, Table 1). The scapular anterior tilting index was significantly lower after PM stretch + SPT than SPT (p < 0.05, Table 1).
UT, LT, and SA muscle activity
The muscle activity of the UT, LT, and SA was significantly greater for PM stretch + SPT than SPT (p < 0.05, Fig. 5).
Discussion
The purpose of this study was to compare SPT and PM stretch + SPT on the PMI, scapular anterior tilting index, scapular upward rotation angle, and UT, LT, and SA muscle activity in subjects with a short PM. To our knowledge, this is the first study to investigate the scapular upward rotators' activity through lengthening of the PM during scapular posterior tilting exercise in subjects with a short PM.
Our results revealed that the PMI and the scapular upward rotation angle were significantly
Conclusions
This study was undertaken to compare SPT and PM stretch + SPT on the PMI, scapular anterior tilting index, scapular upward rotation angle, and UT, LT, and SA muscle activity in subjects with a short PM. The findings of the study showed that the PMI, scapular upward rotation angle, and UT, LT, and SA activity were significantly greater in PM stretch + SPT than SPT in subjects with a short PM. The scapular anterior tilting index was significantly lower after PM stretch + SPT than SPT for subjects
Conflict of interest
The authors have not conflicts of interest to disclose.
Ethical approval
The investigation was approved by Yonsei University Wonju Institutional Review Board.
Funding
The authors have no funding sources to declare.
Acknowledgments
All authors contributed to the concept, design and data collection and analysis of this study. We appreciate with all participants in this study.
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