Scapular kinematic is altered after electromyography biofeedback training
Introduction
Subacromial impingement syndrome (SAIS), or shoulder impingement, is the most common cause of shoulder pain, accounting for 40% of shoulder disorders with an incidence of 19 per 1000 patients (Bot et al., 2005) seen by primary care physicians (Huisstede et al., 2006, Ostor et al., 2005, van der Windt et al., 1995). Impingement syndrome is characterized by a mechanical compression of the soft tissues in the subacromial space (Karduna et al., 2005). SAIS may be the result of a decrease in subacromial space due to altered scapular kinematics, which has been demonstrated in patients with shoulder impingement (Ludewig and Cook, 2000, Warner et al., 1992). Additionally, increased muscle activation of the upper trapezius, in comparison to the lower trapezius and serratus anterior, could lead to changes in normal scapular kinematics (Johnson et al., 1994, Johnson and Pandyan, 2005, Paine and Voight, 2013). These changes can cause shoulder pain as a result of a decreased subacromial space (Karduna et al., 2005, Ludewig and Cook, 2000, Warner et al., 1992).
One of the chief objectives in the rehabilitation of shoulder injuries is re-establishing proper scapular positioning during movement, which is accomplished through retraining the scapular stabilizer muscles (Johnson and Pandyan, 2005, Paine and Voight, 2013). Although, there are clearly underlying biological factors involved, many clinicians feel that abnormal mechanical forces may lead to a pathological progression from impingement syndrome, or tendonitis, to rotator cuff tears.
Education on the correct muscle activation through electromyography (EMG) biofeedback has been shown to be more effective than passive treatment in providing long-term relief from symptoms of impingement (Ma et al., 2011). The technique of EMG biofeedback has been used in clinical settings for rehabilitation of musculoskeletal disorders, and has been employed in rehabilitation programs for patients with shoulder pain (Angoules et al., 2008, Basmajian, 1981, Ehrenborg and Archenholtz, 2010, Flor et al., 1986, Middaugh et al., 2013, Spence et al., 1995). While research interest in this technique has increased in the last few years, still only a handful of studies have been published regarding the use and effectiveness of biofeedback on the improvement of muscle balance in the shoulder (Holtermann et al., 2008, Huang et al., 2013, Weon et al., 2011). These studies have reported favorable changes in muscle activation patterns after the use of biofeedback within one session. However, only Huang et al. (2013) examined the effect of biofeedback on scapular motion, as well as muscle activation patterns during a limited number of rehabilitation exercises. The authors recorded EMG activity of four different scapular muscles in both healthy and shoulder impingement subjects and examined their activation ratios with and without EMG biofeedback training. This study found that EMG biofeedback training resulted in an increase in muscle activity of the serratus anterior, middle trapezius and lower trapezius while decreasing the activity of the upper trapezius. They concluded that EMG biofeedback was beneficial for both groups in improving balance ratios of the scapular muscles (Huang et al., 2013).
It is important to address scapular kinematics in a healthy population, because those who have daily routines involving large amounts of lifting at shoulder level or higher, are at a heightened risk of developing SAIS (Lewis et al., 2005). Construction workers, surgeons, dental care workers, mail carriers, daily computer work, and other occupations, or sports, that require consistent elevation of the arm, include those who are at the greatest risk in the general population (Cools et al., 2007a, Milerad and Ekenvall, 1990, Oberg et al., 1995, Sobti et al., 1997, Vedsted et al., 2011, Wells et al., 1983). Biofeedback has been demonstrated as an effective treatment tool in a pathological population, but there is little investigation utilizing it as a preventative means to reduce the possibility of onset subacromial impingement in a healthy population (Holtermann et al., 2010). Currently, there is a paucity in research that examines the acute effects of exercises with EMG biofeedback in prevention of SAIS. The findings of such study in healthy subjects can help to guide the research endeavors into biofeedback measures in the SAIS patients.
The purpose of the study was to investigate the effects of scapular stabilization exercises utilizing EMG biofeedback training on scapular kinematics in healthy individuals. We hypothesized that after undergoing EMG biofeedback training, the subjects would increase scapular upward rotation, external rotation and posterior tilt.
Section snippets
Participants
There were 23 subjects included in this study (15 males and 8 females) who volunteered. The subjects had a mean age of 23Β±2.9 y/o, mean height 1.75Β±0.1Β m, and mean mass 73.6Β±11.1Β kg. Sample size calculation was performed using the G*Power 3.1.9 (Universitat, Kiel, Germany) with the effect size calculated from the Huang et al. (2013) data of 0.4, alpha level of 0.05, and desired power of 0.8, the minimum study sample needed was revealed as 10 subjects. Subjects were included only if they had no
Results
There was a significant interaction found between time (pre and post EMG biofeedback training) and humeral elevation angle on upward rotation of the scapula (F [1.95, 42.83]=5.72, p=0.007, Ξ·2=0.206, Observed power=0.833). However, the simple effects analyses revealed no significant differences between pre- and post-biofeedback at any humeral elevation angles (p>0.05 for all levels, Fig. 2A).
There was a significant interaction found between time and humeral elevation angle with posterior tilt of
Discussion
The current study was aimed at examining the effects of scapular stabilization exercises with EMG biofeedback training in healthy individuals on scapular kinematics. We hypothesized that after undergoing EMG biofeedback training, the subjects would increase scapular upward rotation, external rotation and posterior tilt during scapular plane humeral elevation. The results of the present study exhibited an effect of the EMG biofeedback training, but only with external rotation of the scapula
Conclusion
In healthy population, scapular stabilization exercises combined with EMG biofeedback training caused the scapula to be in a more externally rotated position during the entire range of motion of scapular plane humeral elevation. This places the shoulder in a retracted position and helps decrease the chance of developing shoulder impingement injuries. However, there were no significant changes observed in scapular upward rotation and posterior tilting.
Conflict of interest statement
The authors declare that there is not conflict of interest that could influence the content of the presented work.
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