Skipping rope - Wikipedia

A Ridiculously Awesome, yet brief, Guide to Double Unders

File:Exercise equipment (rubber ball, light-weight dumbbells, jump rope).jpg - Wikipedia

Long Road Crossfit - According to Skipping Rope in Wikipedia, double unders are performed when, the participant needs to jump up higher than usual while swinging the rope twice under his feet.

Jump Rope Challenge - Wikipedia

How to Chinese Jump Rope: 11 Steps (with Pictures) - wikiHow

File:Michelle Obama and kids double-dutch jump rope - P071511CK-0303 (6047842208).jpg - Wikipedia

This 15-Minute Jump Rope Workout Will Transform Your Arms And Abs

Double Dutch (jump rope) - Wikipedia

Skipping rope - Wikipedia

File:Jump Rope for Heart 060.jpg - Wikipedia

File:Girl playing jump rope.jpg - Wikipedia

Prayer rope - Wikipedia

File:Joaquín Sorolla y Bastida - The Skipping Rope - Google Art Project.jpg - Wikimedia Commons

How to Chinese Jump Rope: 11 Steps (with Pictures) - wikiHow

File:Chinese jump rope Americans pattern.svg - Wikipedia