Jumping rope can be a brutal conditioning tool. Boxers have long jumped rope to get in shape, and more recently jumping rope has been featured in CrossFit WODs. Specifically, CrossFitters do Double Unders, where the rope passes under your feet twice on every jump.

The Double Under is especially difficult. You have to jump extra high so the rope has enough time to make it around twice. You also have to swing the rope extra fast, making it tough to do over and over again.

Although it’s an invaluable endurance training tool, it turns out Double Unders might also be one of the best speed training exercises for youth athletes.

A recent study from Japan looked at how Double Unders relate to speed in youth athletes. The researchers assessed 143 fifth and sixth grade students who had experience jumping rope. They tested how long each student could consecutively perform Double Unders and compared the results to their 20-meter sprint times—the ideal distance for allowing youth athletes to reach their top speed.

Based on the Double Under results, the subjects were separated into a superior and inferior Double Under group. The superior group posted sprint speeds approximately 10 percent (boys) and 5 percent (girls) faster than the inferior group.

The results show that athletes who are better at Double Unders are generally faster. How do the two relate? If you look at the move, the powerful hop and quick rebound actually make it a basic plyometric exercise, which enhances the stretch-shortening cycle, or SSC.

The SSC is a process that occurs in your muscles when your body rapidly changes directions, such as when landing from a jump and jumping up again during the Double Under.

When your feet contact the ground, your thigh and calf muscles lengthen to decelerate your body. The force from the landing is stored as elastic energy. At the bottom of the landing, your muscles make a quick transition—no more than 25 milliseconds—before releasing the stored elastic energy to propel you into the air.

Athletes who have better SSCs have a more powerful sprinting stride and spend less time on the ground, meaning they spend more time moving in the direction they want to go.

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What does this all mean? The Double Under is an ideal exercise for youth athletes to get faster. It’s relatively low impact, doesn’t take much instruction and doesn’t require prior experience training. Plus, it’ kind of fun.

Although this study was limited to youth athletes, the info also applies to advanced athletes who are looking to get faster and more powerful. As long as the Double Under is performed with max effort, it can challenge even the fittest athletes.

In the video above, Ken Vick, High Performance Director for STACK Sports Performance Training, provides key tips for performing the Double Under effectively.

Double Under Coaching Points

• Begin with a single jump and move into Double Unders as you get into your rhythm.

• Imagine being as springy as possible off the ground. Your goals are to spend as little time as possible on the ground and get maximum height from each hop.

• Your knees should bend only slightly when you land on the ground.

• Keep your ankles dorsiflexed (feet toward shins) throughout the exercise.

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