Double unders could probably be classified as the Yugo of CrossFit exercises… they take constant maintenance! This is one exercise that requires a lot of practice to get right, and even more to maintain good technique.
The sting of that jump rope on your bare ankles is a constant reminder to keep practicing!
Rope matters – pick one that comes to mid-chest height when you step in the middle
It’s all in the wrist – maintain loose/relaxed shoulders, chest and back and flip those wrists like crazy!
Try to keep moving – start out with single-unders, get a double under in there, and KEEP GOING, even with single-unders. This will train your body not to stop after that rope goes under twice. Once you get that motion down, try to string double unders in more frequently until you can do them without thinking.