EFFECT OF DIFFERENT SHOULDER POSITION ON EMG PARAMETER OF ROTATOR CUFF AND DELTOID MUSCLE DURING EXTERNAL ROTATION EXERCISE : A CROSS-SECTIONAL OBSERVATIONAL STUDY

Background: The shoulder joint exhibits the greatest amount of motion in the human body. Functional stability is accomplished through the joint capsule, ligaments and glenoid labrum, as well as the dynamic stabilization, particularly the rotator cuff muscles which maintain stability during upper extremity motion. Rehabilitation programs for rotator cuff impingement, repair surgery and athletic conditioning also emphasize strengthening of the shoulder musculature. Altered muscle recruitment will disturb normal scapulohumeral rhythm.

Functional stability of the shoulder is accomplished through the integrated functions of the joint capsule, ligaments and glenoid labrum, as well as the dynamic stabilization of the surrounding musculature, particularly the rotator cuff muscles [1].Thus; the rotator cuff muscles play a vital role in normal arthrokinematics and asymptomatic shoulder functions [2].
Limited external rotation manifested in all shoulder pathologies like rotator cuff tear, impingement syndrome, frozen shoulder etc. External rotation is important part of all activity of daily living like combing hair, grooming, overhead activity etc. Overhead athletes requires adequate strength and endurance of external rotators [2].As per the capsular pattern of shoulder joint, first Limited external rotation is common manifestation in shoulder pathologies [3,4].Findings of EMG activity of rotator cuff and deltoid muscle may be helpful to reduced the load on injured muscle and improve the strength of needed muscle while designing rehabilitation program [2].By providing different shoulder positions, gradual progression of rehabilitation session can be arrange for affected involved muscles.Aims of the study: To see the effect of different shoulder positions on EMG activity of rotator cuff and deltoid muscles during commonly prescribes external rotation exercises.Objectives of the study: 1.To find out effect of 7 different shoulder positions on %MVIC for posterior deltoid muscle.2. To find out effect of 7 differ ent shoulder positions on %MVIC for supraspinatus muscle.3. To find out effect of 7 different shoulder positions on %MVIC for infraspinatus muscle.4. To find out effect of 7 different shoulder positions on %MVIC for teres minor muscle.

MATERIALS AND METHODS
50 Healthy subjects who fulfill inclusion criteria were selected for the study.The entire individuals were providing informed consent and agreed to participate in the study.Inclusion criteria: Age group: 18 to 25 years, Gender: Male and female, Willing to participate Exclusion criteria: subjects with rotator cuff tear and traumatic injury to shoulder, Uncooperative patients, Professional athletes, Subject with cardiac, neurological, psychological condition.Subjects were oriented and explain whole procedure.Prior the testing, Age, gender and 10 RM (repetition maximum) of dominant hand (edinburgh handedness scale) calculated by the use of dumbbell weight and recorded accordingly. 2 All the sites of electrode placements were abraded with sand paper and cleaned with alcohol to minimize the skin impedance.Surface electrodes with a 10mm diameter were placed with electrode gel medium on the target muscle by adhesive tape to assess the EMG activity.The MVIC was taken from the dominant shoulder in the standard manual muscle testing (MMT) position for the best isolation of the targeted muscle. 2 For taking MVIC manual resistance was given by the same person for every subject.

DISCUSSION
minor muscles in the Prone lying lateral rotation exercise than in the Supine lying Lateral Rotation exercise [7].For all 4 muscles, statistically significant differences were noted in the amount of EMG activity across the 7 exercises tested which support the experimental hypothesis.Prone horizontal abduction at 100° with full ER had greatest EMG activity for posterior deltoid, supraspinatus, and infraspinatus.Sidelying external rotation at 0 0 abduction had greatest EMG activity for teres minor muscle.
Present study result were also similar with Blackburn et al (1990), who reported significantly greater activity in infraspinatus and teres minor muscles in the Prone lying lateral rotation exercise than in the Supine lying Lateral Rotation exercise [7].
Teres minor muscle contributes abduction of arm by providing the external rotation but along with subscapularis it contradict their role of elevation and work in weak adduction force which supports present study result [4].Supraspinatus, deltoid, infraspinatus contributes abduction with external rotation by elevation of arm.So, Prone horizontal abduction at 100° with full ER position produced greatest EMG activity [4].
In For all 4 muscles, statistically significant differences were noted in the amount of EMG activity across the 7 exercises tested which support the experimental hypothesis.Prone horizontal abduction at 100° with full ER had greatest EMG activity for posterior deltoid, supraspinatus, and infraspinatus.Sidelying external rotation at 0 0 abduction had greatest EMG activity for teres minor muscle.Present study result were also similar with Blackburn et al (1990), who reported significantly greater activity in infraspinatus and teres

CONCLUSION
The exercise that produced the greatest amount of EMG activity of Teres minor was sidelying ER while deltoid, supraspinatus and infraspinatus prone horizontal abduction at 100° with full ER.Considerations when selecting external rotation exercises may be made based on the amount of infraspinatus and teres minor activity as well as the amount of desired activity of the supraspinatus and deltoid musculature.Limitation of study: Use of Needle electrode will provide better result, while use of surface EMG increases possibility of cross talk between

Table 1 :
). Graph and table shows the mean and SD value of %MVIC of all muscles in all 7 different positions.Posterior Deltoid.
F =75.274, Ex 7 is p <0.0001 significantly different than Ex. 1 and 2 p>0.05Radhika D. Kariya.EFFECT OF DIFFERENT SHOULDER POSITION ON EMG PARAMETER OF ROTATOR CUFF AND DELTOID MUSCLE DURING EXTERNAL ROTATION EXERCISE -A CROSS -SECTIONAL OBSERVATIONAL STUDY.