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

Written by:  Stephen Thomas
Reviewed by: Jeffrey Driban

Related Posts:

Huang HY, Lin JJ, Guo YL, Wang WT, & Chen YJ (2012). EMG biofeedback effectiveness to alter muscle activity pattern and scapular kinematics in subjects with and without shoulder impingement. Journal of Electromyography and Kinesiology PMID: 23123099