Choke or loop a band around something overhead. Step out to the side so you get enough tension on the band so it is still right when you are leaning towards the rack.
Let your hand rest on your head with your palm up to create a fulcrum point so you don't have to use your arm to pull the band. This way your torso is doing all the work.
For some variety, on moderately weighted ab movements such as this, try reversing your breathing. Exhale on the eccentric and inhale on the concentric. This will eliminate any Valsalva help in the movement and put more stress on the musculature. If you're going to use a traditional breathing pattern, try to push your obliques out hard when you crunch down. With this method, you're trying to mimic pushing out on your belt.
Train abs every day you lift. Typically at least 100 reps of a weighted variation. When doing this movement DON'T REST. 25 reps on the right, 25 reps on the left, repeat until all sets are done.
We used a light band in the video. For smaller athletes, I suggest a mini band.