ELECTROMYOGRAPHIC ANALYSIS OF SHOULDER GIRDLE MUSCLES DURING COMMON INTERNAL ROTATION EXERCISES.
BACKGROUND
High level throwing performance requires the development of effective muscle activation within shoulder girdle muscles particularly during forceful internal rotation (IR) motions.


METHODS
Controlled Laboratory Descriptive Study.


OBJECTIVE
To investigate activation pattern of 16 shoulder girdle muscles/muscle sub-regions during three common shoulder IR exercises.


METHODS
EMG was recorded in 30 healthy subjects from 16 shoulder girdle muscles/muscle sub-regions (surface electrode: anterior, middle and posterior deltoid, upper, middle and lower trapezius, serratus anterior, teres major, upper and lower latissimus dorsi, upper and lower pectoralis major; fine wire electrodes: supraspinatus, infraspinatus, subscapularis and rhomboid major) using a telemetric EMG system. Three IR exercises (standing IR at 0° and 90° of Abduction, and IR at Zero-Position) were studied. EMG amplitudes were normalized to EMGmax (EMG at maximal IR force in a standard position) and compared using one-way repeated-measures analysis of variance (ANOVA).


RESULTS
There were significant differences in muscles' activation across IR exercises (p<0.05-p<0.001). Rotator cuff and deltoid muscles were highly activated during IR at 90° of Abduction. Latissimus dorsi exhibited markedly higher activation during IR at Zero-Position. While upper trapezius had the highest activation during IR at Zero-Position, middle and lower trapezius were activated at highest during IR at 90° of Abduction. The highest activation of serratus anterior and rhomboid major occurred in IR at Zero-Position and IR at 90° of Abduction, respectively.


CONCLUSIONS
Studied exercises have the potential to effectively activate glenohumeral and scapular muscles involved in throwing motions. Results provide further evidence for developing rehabilitation, injury prevention, and training strategies.


METHODS
4, Controlled laboratory study.
School of Health Sciences (Sport and Exercise Science), Liverpool Hope University, Liverpool, UK.
Omid
O
Alizadehkhaiyat
Musculoskeletal Science Research Group, Institute of Translational Medicine, University of Liverpool, Liverpool, UK.
David H
DH
Hawkes
Department of Musculoskeletal Biology II, Institute of Ageing & Chronic Disease, Faculty of Health & Life Sciences, University of Liverpool, UK.
Graham J
GJ
Kemp
Musculoskeletal Science Research Group, Institute of Translational Medicine, University of Liverpool, Liverpool, UK.
Simon P
SP
Frostick
Electromyography; Internal Rotation Exercises; Rehabilitation; Shoulder Muscle Activation