The addition of a punching bag to the sit-up machine adds to the fun, and functionality of the exercise. Hit the sandbag in each crunches to enhance the effect of exercise, and venting emotions. We changed the support point to the knee instead of the traditional ankle, thus avoiding ankle injury, and made a certain tilt angle, which allows the knee to better power. These scientific design can make the movement become more safe and efficient. We always follow the concept of giving our customers the best products, so our products are different from other plastic bodies on the market, our bodies are made of metal and have two 4.7-inch oversized suction cups to provide strong suction. The product is used for home gym AB trainer fitness equipment, can be performed at home sit-ups, russian-twist, Sit Ups for Boxing and other abdominal exercise. Please use this product on smooth and flat floors (tile, marble, wooden floors), not on uneven/gap floors/carpeted floors, as they do not create an adsorption effect!