Thin arm exercise: This exercise can not only exercise the chest, but also exercise the shoulders and arms. Sit on the ground with your legs crossed. Hold a ball with both hands (you can also hold it with both hands), and pay attention to make your forearm parallel to the ground. Pinch the ball with both hands and feel the chest force. Please press and hold 1 ~ 2 seconds, and then release. Group 2 repeats this action 20 times.