EMG biofeedback effectiveness to alter muscle activity pattern and scapular kinematics in subjects with and without shoulder impingement
Huang HY, Lin JJ, Guo YL, Wang WT, Chen YJ. J Electromyogr Kinesiol. 2012 Oct 31. pii: S1050-6411(12)00167-8. doi: 10.1016/j.jelekin.2012.09.007. [Epub ahead of print]
Recently, clinicians have focused on reinstituting normal scapular motion to rehabilitate patients with subacromial impingement syndrome (SAIS) since abnormal scapular motions contribute to pain and dysfunction. These abnormal scapular motions may be caused by altered neuromuscular control; for example, the upper trapezius may be more active while the lower trapezius and serratus anterior are inhibited. This imbalance is often difficult to treat and must begin with muscle reeducation. Therefore, the objective of this study was to determine if biofeedback improves scapular motion and neuromuscular control (based on muscle activation ratios: upper trapezius/middle trapezius, upper trapezius/lower trapezius, upper trapezius/serratus anterior) in 12 healthy participants and 13 participants with SAIS. Participants were hooked up to a 3D kinematic system (to measure scapular motion) and electromyography to measure muscle activation in four scapular muscles (upper, middle, and lower trapezius and the serratus anterior). Participants first performed shoulder abduction in the scapular plane to record scapular kinematics. Participants then performed three exercises without and then with biofeedback (side-lying external rotation, forward flexion, and knee push-up). The authors found that biofeedback improved all three muscle activation ratios during the forward-flexion exercise in both groups. When the healthy group performed the side-lying external rotation exercise with biofeedback their upper-to-lower trapezius ratio improved compared to not using biofeedback during the exercise. However, when the participants with SAIS did this exercise with biofeedback their upper-to-middle trapezius and upper trapezius-to-serratus anterior ratios improved compared to not using biofeedback during the exercise. Biofeedback did not influence neuromuscular control during the knee push-up exercise. For scapular kinematics, participants with SAIS had more posterior tipping of the scapula with the use of biofeedback during shoulder abduction.
Rehabilitation of scapular musculature in patients with SAIS is often very challenging due to muscle inhibition and altered firing patterns. This study demonstrated that biofeedback may improve muscle activation ratios, which is an indicator of neuromuscular control. Commonly the upper trapezius is over active and because of its size and strength it can easily alter the scapular upward rotation force couple thereby causing a scapular shrug rather than smooth coordinated upward rotation. Biofeedback can be used to allow the patient to figure out how to decrease activity of the upper trapezius and increase their lower trapezius and serratus anterior activity. Therefore, this modality would be very beneficial during the initial stages of rehabilitation to reeducate and improve neuromuscular control. This study utilized a visual form of biofeedback that allowed the participant to see the live muscle activity; however, there are many other forms of biofeedback that can be used. Another form of visual feedback is the use of mirrors so that the patient can observe the motion of the scapula and relate it to their voluntary activation. Auditory feedback is another alternative that uses a beeping sound that increases in frequency with a stronger contraction of a specific muscle. Proprioceptive feedback can also be used in terms of scapular tape or bracing to enhance neuromuscular activation. Based on these results visual biofeedback is an easy way to improve muscle activity ratios in patients with SAIS. Future clinical trials should evaluate if improving muscle activity ratios improves patient-reported outcomes. Do you use any form of biofeedback with your SAIS patients or even for other injuries? What forms of biofeedback do you use or find effective?
Written by: Stephen Thomas
Reviewed by: Jeffrey Driban
Adaptations of Shoulder Joint Stiffness may Lead to Increased Muscle Efficiency and Neuromuscular Control