Effects of 3 Infraspinatus Muscle Strengthening Exercises on Isokinetic Peak Torque and Muscle Activity

Abstract

Context: The infraspinatus muscle plays a particularly important role in producing primary external rotation (ER) torque and dynamic stability of the shoulder joint. Previous studies have reported that prone external rotation with horizontal abduction (PER), side-lying wiper exercise (SWE), and standing external rotation (STER) were effective exercises for strengthening the infraspinatus. However, we do not have enough knowledge about changes in muscle strength and dynamic muscle activity in each exercise under dynamic conditions. Objective: To compare the ER muscle strength, muscle activity among exercise methods and between muscle contraction types during 3 different exercises. Design: Repeated measures design in which ER muscle strength and muscle activities data were collected from subjects under 3 exercise conditions. Setting: Outpatient clinic. Participants: A total of 15 healthy men with no shoulder, neck, or upper-extremity pain were participated. Intervention: The subjects performed 3 different exercises randomly in concentric and eccentric using a Biodex dynamometer at an angular velocity of 60°/s. Main Outcome Measures: The ER peak torque (PT) data was collected and surface electromyography was used to measure the activity of the infraspinatus and posterior deltoid muscles and infraspinatus to posterior deltoid muscle activity ratio. Results: There was significant main effect for muscle contraction type in ER PT (P < .05). The concentric PT was greater during PER (P < .05) and SWE (P < .05) compared with eccentric. The main effect for exercise was found in ER PT and muscle activity (P < .05). The ER PT and infraspinatus muscle activity were the largest increased during PER whereas the lowest during STER in both concentric and eccentric (P < .05). Conclusion: The results of this study suggest that PER is an exercise for strengthening the infraspinatus muscle effectively.