Back in the mid-1950s, Dr. Arthur Steindler introduced the concept of open kinetic chain (OKC) and closed kinetic chain (CKC) movements. In a nutshell, an OKC movement is any movement where the terminal segment (i.e., the distal end of the extremity of interest) is free to move in space, and a CKC movement is any movement where the terminal segment is restrained against an immovable object or surface.

Think of a leg extension versus a squat. It’s pretty easy to tell which is an OKC movement and which is a CKC movement, but what about a leg press? One camp says OKC; the other says CKC. Rather than debate who’s right and who’s wrong, I have another way of defining these terms: an OKC movement is any movement where you move an object around your body, and a CKC movement is where you move your body around an object (or more specifically, around an immovable object or surface). So a lat pulldown would be considered an OKC movement and a pull-up a CKC movement.

It’s far more neurologically demanding to move your body around an object rather than vice versa. For one, greater core stability is required – most of the time you’re not sitting on a seat or lying on a bench. Of course, the other obvious factor is that a greater amount of bodyweight (BW) is being lifted. For these reasons, strength gained from a CKC movement will typically transfer to its OKC equivalent, but not vice versa.

Let’s look at an example. The average 200-pound male trainee that’s been at the weight game for awhile should easily be able to rep out on prone leg curls with 100+ pounds. Now ask that same guy to rep out on the Nordic hamstring curl with just his BW – and I mean full range of motion reps – and he’ll struggle. (By the way, most guys lift just over 50% of their BW on the Nordic exercise, and that’s assuming they make it at least halfway to the ground.) So the prone leg curl (the OKC movement) will not transfer to the Nordic hamstring curl (the CKC movement), but if you can increase your strength on the latter, it will improve the former. Got it?

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.