This exercise is used to strengthen the abdominal muscles by adding resistance to a standard crunch.
There are many different machines that replicate the crunch, but they are all pretty similar. Begin by selecting a weight that you can comfortably handle and then sit in the machine. Place your feet under the pads and reach up to grab the handles above your head. Make sure that your arms form a 90 degree angle once you have the handles in your hand. On different machines, there will be a pad across your chest; if this is the case make sure it is at chest level and then cross your arms around the pad. Now, squeeze your abs and crunch your torso by pulling the weight down with your abs. Squeeze your abs and then slowly return to the starting position.
Make sure that your arms remain stationary throughout this movement; many lifters will use their arms to pull the weight down, but that will not help your abs. Also, control the weight throughout the movement and focus on your abs.