Background: Pressure biofeedback may facilitate selective rotator cuff activation during shoulder external rotation, but training effects and structural changes are unclear. Objectives: To examine the effects of a 4-week external rotation program with pressure biofeedback on shoulder muscle activity and rotator cuff thickness. Design: Quasi-experimental design. Methods: Thirty healthy adults were randomized to experimental (n=15) or control (n=15). Both performed seated external rotation at 30° with an elastic band (3×12 reps, 4 sessions/week, 4-week); the biofeedback group maintained 40 mmHg scapular adduction pressure. Surface EMG (%MVIC) and ultrasound muscle thickness were assessed pre/post. Paired and independent t-tests were used (α=.05). Results: In the experimental group, teres minor and infraspinatus activity increased, whereas middle and posterior deltoid activity decreased (P<.05). Post-intervention, rotator cuff activity was higher and posterior deltoid activity was lower versus control (P<.05). Muscle thickness showed no significant changes. Conclusions: A 4-week pressure biofeedback training program changed muscle activation during shoulder external rotation by increasing rotator cuff activation and decreasing compensatory deltoid activity. These findings indicate meaningful neuromuscular adaptations during the external rotation task.

INTRODUCTION
SUBJECTS AND METHODS
    Subjects
    Outcome Measures
    Data and Statistical Analysis
RESULTS
DISCUSSION
CONCLUSION
FUNDING
CONFLICTS OF INTEREST
AUTHOR CONTRIBUTIONS
REFERENCES

• Chihwan Kim(Department of Physical Therapy, Kaya University, Gimhae, Republic of Korea)
• Soohan Kim(Department of Physical Therapy, Kaya University, Gimhae, Republic of Korea) Corresponding author