An investigation into EMG activity in the upper and lower portions of the subscapularis muscle during normal shoulder motion.
OBJECTIVE
The subscapularis (SSc) muscle is considered to perform a variety of roles during normal shoulder movement. The SSc is innervated by two or more discrete motor nerves and previous studies have indicated some difference in electromyographic (EMG) activity between the upper and lower portions of the muscle. The purpose of the present study was to compare EMG activity between the upper and lower portions of the SSc muscle during voluntary shoulder movements in normal healthy subjects.


METHODS
Eight subjects were evaluated. A pair of intramuscular electrodes was inserted into each portion of the muscle. EMG data were recorded during the following movements: sagittal flexion; abduction in the coronal plane; and abduction in the scapular plane.


RESULTS
EMG onset of the upper portion of subscapularis occurred significantly earlier compared to the lower portion. Differences were also seen in the level and pattern of activation between the two portions, with upper SSc demonstrating higher levels of activation than the lower portion.


CONCLUSIONS
These findings suggest that the upper and lower portions of SSc are differentially active during voluntary shoulder movements.
O'Connell
Neil E
NE
School of Health and Social Care, Brunel University, UK. neil.oconnell@brunel.ac.uk
Cowan
Joseph
J
Christopher
Tony
T
D004576:Electromyography; D006801:Humans; D009043:Motor Activity / Q000502:physiology; D009046:Motor Neurons / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D012046:Rehabilitation / Q000379:methods; D012785:Shoulder Joint / Q000502:physiology*