We're big fans of the nordic curl, and have highlighted many variations of it in the past. However, this one by @trustmephysiotherapist takes the cake. In comparison to the lat pull down variation we recently posted (2nd clip), this is a lot safer. You don't need to worry about accidentally landing on your face and it doesn't require you to find the most appropriate amount of resistance before beginning. In comparison to the push up variation (3rd clip), this doesn't require nearly the amount of upper extremity (chest/tricep) strength that many are lacking (ie youth athlete).
Furthermore, with this variation you get a GREAT added benefit of some core work. At the fully rolled out position, it's essentially a plank on a swissball. Similar to the "stir the pot" exercise - without the stirring of course. If you're more limited by core strength -- hamstring strength while doing this variation, then you just discovered a BIG TIME limitation aka a WEAK LINK that you need to fix with some #prehab ASAP!!
Give it a shot and let us know what you think!