Chain lifts add resistance to both barbell work and bodyweight movements. With barbell work, we refer to this resistance as accommodating resistance. This form of resistance allows equal difficulty during all parts of each movement. At the bottom of the rep (when you are at your weakest), the chains rest on the ground, relieving some of the resistance. At the top of the rep (when you are at your strongest), the chains lift off the ground creating more resistance. For bodyweight movements, chain lifts simply provide more resistance throughout the movement than there would be using just bodyweight.