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Stacy T. Makino

Muscle Activation During Therapeutic Exercises of the Shoulder

Purpose
To identify muscle-firing characteristics and there determine the exercises which target the supraspinatus (SUP), subscapularis (SUB), infraspinatus (INF) and teres major (MAJ).

Subjects
Fifteen college students between the ages of 20-22 reported to the Human Performance Laboratory for participation. Subjects must not have experienced a subluxation or dislocation episode, and currently have no pain in their dominant arm and shoulder.

Method
After completing the approved informed consent form demographic data was collected (Height, Weight, Age, Dominant arm). Subjects then were introduced to a series of rehabilitation exercises: 1 - 90/90 Internal Rotation (IR), 2 - 90/90 External Rotation (ER), 3 - Neutral (NEU) IR, 4 - NEU ER, 5 - Scaption (SCAP) IR, 6 - SCAP ER, 7 - Lat Pull, and 8 - Horizontal Abduction . Once they were comfortable with the exercises they were prepped for the insertion of the electrodes. After insertion subjects randomly completed each exercise. Electromyographic data was collected during each exercise.

Measurement
For each subject muscle activity was collected using electromyography. Data was first filtered using a Blackman -67 (20-100 mHz) bandpass filter and then rectified. Five repetitions (3-7) per exercise were used in analysis. The integral and delta s were extracted from each repetition

Results
A 2-way repeated measure ANOVA, alpha = 0.05, was run to identified significance and followed with a Tukey HSD Post-hoc analysis. Significance in the interaction between the muscle and motion was identified. For the SUP, 90/90 ER elicited the most muscle recruitment. The INF and MAJ, were both recruited greater during 90/90 ER and SCAP ER exercises.

Discussion
Recruitment during 90/90 ER, and SCAP ER was significantly greater for the SUP, INF, and MAJ. With the 90/90 ER being slightly higher than the SCAP ER motion. Recruitment during 90/90 ER and SCAP ER was significantly greater than other motions for the MAJ, the authors feel that this may be due to decreases in ER strength and therefore substitution.

Conclusion
External rotation at 90/90 and in scaption elicit the most muscle recruitment for the SUP, INF, and MAJ and therefore should be staples in rehabilitation protocols for the Glenohumeral joint.

Mentor:  Brian Hatzel

Page last modified May 13, 2011