A double under is a popular exercise done on a jump rope in which the rope makes two passes per jump instead of just one. It is significantly more effective than a single rope pass in that it allows for higher work capacity.
The "double under" first appeared on CrossFit.com March 9, 2001.
The Double Under takes a bit of coordination and determination to master. Those with less coordination will find it a little more difficult.
The Double Under must be executed with more intensity in order to complete a high number of repetitions without mistake.
The main key to Double Under success is learning how to control the rope. Rope control will help you coordinate your jumps to the whipping of your wrist.
Their are several programs of instruction that have been produced to help individuals conquer the double under. Two of the top programs available are http://doubleundertraining.com and Molly Metz's Jumpnrope.com team.
Many athletes prefer to use speed ropes specifically designed for Crossfit training made of a thin wire cable as this makes it easier to achieve double unders.