How to Use leg curl machine properly?

The leg curl, is the most popular hamstring (rear thigh) exercise; unfortunately, performing this exercise incorrectly is also quite popular. In general, you don’t want to allow your butt to stick up in the air as you exercise (with the exception of the downward-facing dog exercise in yoga). When you’re doing an exercise such as the push-up or plank, if your butt is in the air, it means that you’re relying more on your legs instead of your abdominals to stabilize your torso. In the case of certain machine exercises, sticking your butt up in the air means you’re not isolating the correct muscle group.

Using the leg curl machine the wrong way
Watch people use the leg curl machine and you’ll see that as they kick their legs toward their butt, their hips lift off the support pad, and their butt sticks up about 2 inches. This mistake is subtle, but it’s a sneaky way of taking work away from your hamstrings and transferring the effort to your hip muscles, allowing the hamstrings to avoid doing the work that they need to do to get stronger. See photo A

Using the leg curl machine the right way
To prevent your hips from popping off the pad, raise your upper thighs just a hair off the pad before you bend your knees for the kick upward. In this position, you feel your hamstrings working a lot harder. See photo B