A study of effective exercise methods and resistance intensity for selective strengthening of the infraspinatus muscle

BackgroundTo selectively strengthen target muscles, resistance intensity as well as limb position should be considered.ObjectiveThis study aimed to identify the most effective exercise positions and the optimal resistance intensity to selectively strengthen the infraspinatus muscle.MethodsThis study included 18 healthy men who underwent four different external rotation (ER) exercises in prone external rotation (PER), side-lying wiper, sitting external rotation, and standing external rotation (STER) exercise by varying the shoulder positions under low, medium, and high resistance intensity conditions randomly. Infraspinatus and posterior deltoid muscle activities and the infraspinatus to posterior deltoid activity ratio were measured based on ER exercise positions and resistance intensities.ResultsThis study revealed a significant interaction and main effects of exercise position and resistance intensity on muscle activity and muscle activity ratio. Both muscle activities were increased as the resistance intensity increased, but the muscle activity ratio was decreased. Infraspinatus muscle activity and muscle activity ratio were higher in the PER and STER exercises than in other exercises.ConclusionWe indicate that PER and STER are effective exercises to selectively strengthen the infraspinatus muscle. Additionally, performing the exercise at low or medium resistance intensity rather than high resistance intensity is recommended to activate the infraspinatus selectively while minimizing the involvement of the posterior deltoid.