Keep tension on the hamstrings by keeping your hips down as you lift the weight up.
If there is one exercise you are strong on, chances are it is the leg curl. Lie down on any leg-curl machine and for some reason, you can just pull the heck out of it, right? Well, that is good, but it can also be bad if you allow yourself to get sloppy. Hamstrings in general are pretty powerful. You can pull a lot with your hamstrings, but when it comes to the leg curl, you have to remember that it is an isolation exercise. Many athletes/bodybuilders try to turn it into a compound, multi-joint exercise, by raising their hips off the bench as they curl the weight even though it is only supposed to be an isolation move. Even though you might be able to curl more weight or do a few extra reps with that kind of hip action, you are actually making the exercise easier because you are removing the work form the hamstrings.
The key is to imagine that you have glued your hips to the bench throughout the set. Although you may need to lower the weight in order to achieve proper form, your hamstrings will still bear most of the burden, which is what you really want anyway. In fact, if you want another way to burn the hams and glutes without cheating the lift, then after you have curled the weight up and your heels nearly touch your glutes, try raising your quads an inch or so off the bench. That small movement will help burn your upper hams and glutes even more without sacrificing form.
Lie facedown on a leg-curl machine and position your Achilles¬ tendons below the padded leverwith your knees just off the edge of the bench. Grasp the bench or the handles for stability. Make sure your knees are slightly bent to protect them from over-extension.
Contract your hamstrings to raise your feet towards your glutes in a strong but deliberate motion, squeezing the muscles at the top, and then lowering under control back to the start position. Do not allow the weight stack to touch down between reps. S
Leg Remedy: Lying Leg Curl Corrected
As mentioned previously with the hack squat exercise you can also turn your toes in and out for a different stimulus on the leg curl (an open-chain move). Turn your toes in to target the inner hamstrings, and out for the outer hamstrings. Squeezing your hamstrings at the top when your hips are pressed into the bench will further ignite the muscle fibres or the back of the leg. But be careful not to raise your hips, or you will lose much of that tension.