A good way to get strong on the Nordic hamstring curl is to use accommodating assistance from a lat pulldown machine but done in a special manner. Here’s how it works.
Kneel on the seat facing away from the machine, and secure the back of your ankles against the knee support. Instead of using the high cable for assistance though, use a resistance tube – secure it on the machine itself or thread it through the high pulley attachment ring (just make sure to put the pin through the heaviest plate). Now, perform the exercise as you normally would from the ground while holding on to the tube for dear life!
As you descend further down into the movement and take on more of your BW, the tube will provide greater assistance. This converts a once almost undoable exercise for many guys into a winner. Try it, you’ll welcome the hamstring soreness the following day!
By the way, if you have a SITFIT available, use that to kneel on. I find that it not only helps with comfort but facilitates weight shifting and prevents you from sliding down the seat.