One Arm Chest Fly Exercise One-arm variation of the Chest Fly. An asymmetrical work that strongly activates many stabilizing muscles, mainly the external obliques on the active side and the internal obliques on the opposite side. The target 🎯 muscle as you can see in the left pic is the Pectoralis major, Costal Division. https://www.muscleandmotion.com/products/strength-training-app/ | Muscle and Motion