Muscle and Motion on Instagram: "📚 Shoulder External Rotation at 0° vs. 90° A study by Kurokawa et al. (2014) revealed how muscle engagement changes with arm position during shoulder external rotation. 🔹 At 0° abduction: The infraspinatus does most of the work, powering the movement when your arm stays close to your body. 🔹 At 90° abduction: The teres minor takes over, showing peak activation when your arm is raised to the side. 💪 Understanding these differences helps you train smarter, enha