Check out this great video from Scott Herman Fitness showing you how to properly execute a rack pull.
The rack pull is a great exercise to help increase your maximum lift on your deadlift. You’ll be activating a lot of muscles to perform this movement. Although there will be more emphasis placed upon your hamstrings, glutes, quads and forearms, you’ll also be activating your traps, back, shoulders, hip flexors, calves and core (lower back, abs and obliques).
This exercise allows you increase your explosiveness by focusing on the sticking point of the deadlift which is bringing the barbell up an over your knees by squeezing you glutes and pushing through your hips.
By starting the lift a few inches below your knees, you can take out the first half of the movement which will allow you to perform the exercise with more weight than if you were to deadlift from the ground. The most important thing to remember is that you want to use the same form or set-up that you would when performing a traditional deadlift. Also, don’t go too crazy on the weight. I suggest starting off with 30 – 40 pounds more than the weight you would use for a set of 8 – 10 reps on your deadlift
via Scott Herman Fitness