As we all know, the double under is and will continue to be a mainstay in the crossfit world, so its important that we develope and improve this skill. Her is a great video from HQ with some very helpful double under tips.
Exercise: 100 Single unders, 100 single leg single unders( 50 each leg), 100 Double unders( Try this as a warm up 3 times per week, it wont take that long but will show some improvements.)
