Acromiohumeral Distance During Neuromuscular Electrical Stimulation of the Lower Trapezius and Serratus Anterior Muscles in Healthy Participants

Abstract

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 (t(19) = -3.89, P = .004), SA muscle (t(19) = -7.67, P = .001), and combined LT and SA muscles (t(19) = -5.09, P = .001). We observed no differences in the increased acromiohumeral distance among the 3 procedures (F(2,57) = 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.

Keywords: real-time ultrasound; rehabilitation; subacromial impingement syndrome.

Figures

Figure 1.

Standardized participant position.

Figure 2.

Lower trapezius muscle stimulation.

Figure 3.

Serratus anterior muscle stimulation.

Figure 4.

Combined lower trapezius and serratus anterior muscle stimulation.

Figure 5.

Ultrasound image shows the shortest tangential measure between the hyperechoic landmarks of the most superior aspect of the humerus and acromion.