The Shoulder Prone I Exercise
The prone shoulder I exercise, also known as shoulder extension in external rotation, is one of four very basic activities known as the T-Y-I-W series of upper body exercises typically performed in a prone position, which activate and strengthen posterior shoulder girdle muscles.
Ronai, P. (2018). The shoulder prone I exercise. ASCM's Health & Fitness Journal, 22(2), 30-33. doi: 10.1249/FIT.0000000000000371