Analysis of the scapulohumeral rhythm and electromyography of the shoulder muscles during elevation and lowering: comparison of dominant and nondominant shoulders.
OBJECTIVE
Assessment of whether elevation and lowering of the dominant and nondominant arms occur in a similar manner in healthy individuals is clinically important in terms of shoulder disorders.


METHODS
We examined the scapulohumeral rhythm (SHR) and performed electromyography (EMG) for the middle deltoid, upper trapezius, lower trapezius, and lower part of the serratus anterior muscles of both shoulders in 18 healthy volunteers (14 men, 4 women) with a mean age of 24 years (range, 19-30 years). The participants randomly elevated and lowered either the right or left arm in the scapular plane, and the motion was measured using a 3-dimensional motion analyzer.


RESULTS
The average angles of maximum arm elevation and scapular upward rotation were 130.3 degrees +/- 7.9 degrees and 32.2 degrees +/- 5.6 degrees, respectively, for dominant arms, and 130.8 degrees +/- 6.4 degrees and 31.8 degrees +/- 5.8 degrees, respectively, for nondominant arms. The SHR in each 10 degrees increment did not differ significantly between the dominant and nondominant arms in each participant during elevation (P = .337) and lowering (P = .1). A significant difference was found in the percentage integrated EMG (%IEMG) of the lower trapezius between the 2 shoulders (P < .049).


CONCLUSIONS
If the kinematic difference is identified between both shoulders, we can predict the dysfunction or disorder in shoulder complex. Moreover, we should evaluate how shoulder muscles are used and whether the muscle becomes weak.


CONCLUSIONS
Healthy individuals elevate and lower the dominant and nondominant shoulders in a similar kinematical pattern despite 3 of 4 muscles indicating different EMG activities between both shoulders.
Yoshizaki
Kunio
K
Koriyama Institute of Health Sciences, Koriyama, Fukushima, Japan; Interdisciplinary Graduate School of Science and Technology, Shinshu University, Ueda, Nagano, Japan. k-yoshi@k-tohto.ac.jp
Hamada
Junichiro
J
Tamai
Kazuya
K
Sahara
Ryo
R
Fujiwara
Takayuki
T
Fujimoto
Tetsuya
T
D000328:Adult; D000704:Analysis of Variance; D015331:Cohort Studies; D004576:Electromyography; D005260:Female; D007839:Functional Laterality; D006801:Humans; D006811:Humerus / Q000502:physiology; D008297:Male; D009068:Movement / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D011336:Probability; D016059:Range of Motion, Articular / Q000502:physiology*; D012016:Reference Values; D015203:Reproducibility of Results; D012540:Scapula / Q000502:physiology; D012785:Shoulder Joint / Q000502:physiology*; D055815:Young Adult