This exercise targets the quadriceps, glutes, and hamstrings. Much like the squat, it is a "midrange" motion, and should be performed as an alternative to squats as a primary mass building exercise. It is a much simpler exercise, and I will sometimes use this with beginners until they develop a bit of a foundation before moving them into squats.

If the machine you are using has an adjustable back then adjust it to your comfort. For heavy lifting I prefer the back position to be leaned back more. There are many foot positions you can use on this exercise, but for now let's use the standard form. Place your feet about shoulder's width apart approximately in the middle of the platform. Raise the weight and lower the safeties (the catches that the sled rests on) but DO NOT lock your legs. Hold the handgrip to hold you down (if you don't use this, you may get pushed out of your seat). You are ready to start.

Lower the weight slowly, about 3-5 seconds, breathing in. Come all the way down until your legs are almost flat against your body. Pause briefly, then press the weight to the top position, exhaling on the positive portion of the motion. The positive motion should take about 1-3 seconds. Don't "pop" the weight up... That could be really hard on the knees.

Here are two variations you can do on the same machine: To focus on the "tear drop" muscle (vastus medialis) position your feet where the heels are touching and the toes are pointed out. If you want to recruit more from the glutes and hamstrings, raise foot position a little higher and go a little wider than shoulder's width.