Context
Compromise to the acromiohumeral distance has been reported in participants with subacromial impingement syndrome compared with healthy participants. In clinical practice, patients with subacromial shoulder impingement are given strengthening programs targeting the lower trapezius (LT) and serratus anterior (SA) muscles to increase scapular posterior tilt and upward rotation. We are the first to use neuromuscular electrical stimulation to stimulate these muscle groups and evaluate how the muscle contraction affects the acromiohumeral distance.
Objective
To investigate if electrical muscle stimulation of the LT and SA muscles, both separately and simultaneously, increases the acromiohumeral distance and to identify which muscle-group contraction or combination most influences the acromiohumeral distance.
Design
Controlled laboratory study.
Setting
Human performance laboratory.
Patients or Other Participants
Twenty participants (10 men and 10 women, age = 26.9 ± 8.0 years, body mass index = 23.8) were screened.
Intervention(s)
Neuromuscular electrical stimulation of the LT and SA.
Main Outcome Measure(s)
Ultrasound measurement of the acromiohumeral distance.
Results
Acromiohumeral distance increased during contraction via neuromuscular electrical stimulation of the LT muscle (
t19 = −3.89,
P = .004), SA muscle (
t19 = −7.67,
P = .001), and combined LT and SA muscles (
t19 = −5.09,
P = .001). We observed no differences in the increased acromiohumeral distance among the 3 procedures (
F2,57 = 3.109,
P = .08).
Conclusions
Our results supported the hypothesis that the muscle force couple around the scapula is important in rehabilitation and scapular control and influences acromiohumeral distance.Key Words:
subacromial impingement syndrome, real-time ultrasound, rehabilitationKey Points
- Acromiohumeral distance increased during neuromuscular electrical stimulation of the lower trapezius muscle, serratus anterior muscle, and combined lower trapezius and serratus anterior muscles.
- The increase in acromiohumeral distance was not different among the 3 neuromuscular electrical-stimulation procedures.
- The muscle force couple around the scapula is important in rehabilitation and scapular control and influences acromiohumeral distance.
Optimal upper limb function depends on the ability to statically and dynamically position the shoulder girdle in an optimal coordinated fashion.
1,2 Suboptimal motor control is considered a risk factor for developing shoulder subacromial impingement syndrome.
3–14 Alterations in scapular motion have been linked to a decrease in serratus anterior (SA) muscle activity, an increase in upper trapezius muscle activity, and an imbalance of forces between the upper and lower parts of the trapezius muscle.
15 This may adversely affect scapular positioning, resulting in reduced scapular upward rotation, increased anterior scapular tilt, and scapular winging.
4,9,16 In turn, scapular upward rotation and posterior tilt are considered vital for elevating the acromion and, hence, widening the subacromial space, thereby preventing impingement of the subacromial tissues.
17,18 Atalar et al
19 suggested that reduced scapular mobility led to a decrease in acromiohumeral distance (AHD) during upper extremity abduction. Therefore, when developing rehabilitation strategies for patients with subacromial impingement syndrome, correcting neuromuscular control of the SA and trapezius muscles is important.
20,21Overall, researchers
22,23 have supported the theory that altered activity in the scapular rotator muscles is present in patients with subacromial impingement syndrome and have highlighted the role of scapular rotator muscle training as an essential component of shoulder rehabilitation. A clinical practice strategy, supported by research data, recommends that patients who have subacromial shoulder impingement and present with primary movement dysfunction of the scapula should be given strengthening programs targeting the lower trapezius (LT) and SA muscles.
24,25 The LT muscle is reported to increase posterior scapular tilt, and the SA muscle is believed to increase upward rotation of the scapula.
2 In turn, posterior scapular tilt and upward scapular rotation are associated with increased AHD.
17,18Authors
9,23,26–29 of electromyographic (EMG) studies have tested muscle activity in participants with subacromial impingement syndrome and in healthy persons. In patients with subacromial impingement syndrome, when the upper extremity was at rest and during flexion and abduction, the EMG signal amplitude of the upper trapezius muscle increased, whereas the EMG signal amplitude of the LT and SA muscles decreased.
30,31 These researchers have considered the immediate changes in the surface EMG activity of the scapular rotator muscles. However, to our knowledge, we are the first to use neuromuscular electrical stimulation (NMES) to stimulate the muscle groups of the LT and SA and evaluate the effect of muscle contraction in these muscles on the AHD. Neuromuscular electrical stimulation is used for various medical applications and is a common intervention during rehabilitation to improve function and motor control,
32 prevent and treat shoulder pain,
33 increase range of motion,
34 and facilitate changes in muscle action and performance.
35 Therefore, the purpose of our study was to investigate whether stimulation of the LT and the SA muscles (separately and simultaneously) with NMES would increase the AHD and to investigate which muscle-group contraction or combination most influenced the AHD.
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