What is Double-under?

What is Double-under?

A double-under is a jump rope rep where the rope travels under your feet twice for every one jump you take. In CrossFit it is written as DU on the whiteboard, and each double-under counts as a single rep even though the rope makes two passes. The skill sits one level above the single-under, where the rope passes once per jump, and it shows up constantly in benchmark workouts such as Annie (50-40-30-20-10 double-unders and sit-ups) and many Open workouts.

What makes the double-under hard is not fitness but timing. You do not jump twice as high; you jump only slightly higher than a single-under, roughly 5 to 15 centimeters off the floor, and spin the rope about twice as fast using your wrists. The feet stay together, the elbows stay close to the ribs, the hands sit just in front of the hips, and the body holds a tall hollow position so you land in the same spot you left.

Because the rope has to clear the feet twice in the short window you are airborne, everything has to be quick and compact. Most beginners fail not because they lack the jump but because they whip the rope with their whole arms, pike at the hips to reach for extra height, or bend the knees to tuck the feet up. Learned properly, the double-under is one of the most efficient conditioning tools in the gym: it spikes the heart rate fast, builds calf and forearm endurance, and rewards precision over raw effort.

How it works

Mechanically, a double-under works by matching rope speed to hang time. During one jump you are only off the floor for a fraction of a second, so the rope must complete two full revolutions in that window. Rope speed comes almost entirely from the wrists: with the hands fixed just in front of the hips and the elbows tucked, small, fast circles of the wrists move the rope tips through two arcs while the arms stay quiet.

If the rotation comes from the shoulders or elbows instead, the arc gets long and slow and the rope cannot complete the second pass before you land. The jump itself is a stiff, ankle-driven bounce, more like a pogo stick than a squat jump. You stay tall through the hips and knees, push through the balls of the feet, and use the calves and the elastic recoil of the Achilles tendon to rebound, which is why sustained double-unders are so taxing on the lower legs.

The core holds an isometric hollow position so the pelvis does not pike; piking to gain height actually shortens hang time because it drops the feet late. Timing is the third piece: the wrists snap the second rotation right at the top of the jump, so the rope reaches the floor just as your feet clear it and passes again before you land.

Coordinating the fast double wrist-snap with a single, well-timed bounce is a motor-learning problem, which is why the skill improves in sudden jumps once the pattern clicks rather than smoothly with fitness. Rope length and material matter too: a rope sized so the handles reach the armpits when you stand on the middle, and a lightly weighted or stiff cable, both give the feedback that makes the timing easier to feel.

How to apply it

• Build unbroken single-unders first: Before attempting double-unders you should string together 40-50 single-unders without tripping, jumping from the balls of the feet with quiet arms. This proves you own the rhythm, the relaxed grip, and the ankle bounce the double-under is built on.
• Practice the power jump: Do single bounces slightly higher than normal without the rope, landing softly and rebounding immediately. This trains the taller, stiffer jump and the fast landing absorption a double-under needs, so you are not learning height and timing at the same moment.
• Penguin taps for the double wrist-snap: Jump once and tap your thighs twice quickly with the handles while the rope stays behind you. The two taps rehearse the exact double wrist rotation of a double-under against a single jump, teaching the hands to move twice as fast as the feet.
• Use the 3-1 drill (big singles into a double): Perform three slow, high single-unders, then whip one double-under, then reset. Alternating trains your body to insert the fast double rotation into a familiar rhythm without stringing failures together, and it is the fastest bridge from one DU to several.
• Keep hands low and wide, elbows pinned: Fix the hands just in front of the hips, a little wider than the body, with the elbows tucked to the ribs. This shortens the rope arc so it can complete two passes, and stops the common fault of raising the hands as you fatigue, which shrinks the loop and causes trips.
• Add reps in small, unbroken sets: Progress from a single DU to 2, then 3, then 5 in a row, resetting form between attempts rather than grinding through trips. Chasing clean, unbroken clusters trains the timing far better than accumulating messy reps under fatigue.

Types

Worked example

A four-step progression that takes someone with solid single-unders to their first strings of double-unders. Each step is owned before moving on, and reps stay submaximal so timing does not fall apart under fatigue.

Most people get their first double-under within one to three focused sessions of the 3-1 drill, then progress from one rep to unbroken sets of five over a few weeks. The skill tends to click suddenly rather than improve smoothly, so short, frequent practice beats long grinding sets.

Double-under vs single-under

Single-unders are the foundation and the scale: when double-unders break down in a workout, athletes often substitute single-unders (commonly at a 2-to-1 or 3-to-1 rep ratio) to keep the heart rate up while protecting form.

By goal

• Beginners learning the skill: Practice double-unders fresh, not fatigued, in short daily sets. Master unbroken single-unders first, then drill penguin taps and the 3-1 pattern. Expect the skill to appear suddenly; a few minutes most days beats one long frustrating session.
• CrossFit and conditioning: Once you can string double-unders, practice them under light fatigue so they hold up mid-workout. Learn a scaling plan in advance, such as swapping to single-unders at a 2-to-1 ratio when your set breaks, so a workout does not stall on the rope.
• General fitness and fat loss: Double-unders are a high-rate, low-cost cardio tool: roughly 190-225 calories in ten minutes for a 150-pound person. Use short intervals, for example 30 seconds on and 30 off, and stop each set when timing degrades rather than tripping repeatedly.

Common misconceptions

• "You need to jump much higher to fit two passes in." You jump only slightly higher than a single-under, about 5 to 15 cm. Extra height comes at the cost of a stiff, quick landing and usually leads to piking or knee-tucking. Speed comes from the wrists spinning the rope faster, not from more airtime.
• "Double-unders are mostly a fitness or cardio problem." They are primarily a timing and coordination skill. Very fit athletes often fail their first attempts, while the skill clicks suddenly once the double wrist-snap syncs with the jump. Practice the pattern fresh; conditioning follows once the movement is reliable.
• "Whip the rope harder with your arms to get it around twice." Power comes from small, fast wrist circles with the elbows pinned to the ribs and hands near the hips. Swinging from the shoulders lengthens the rope arc and slows it down, so the second pass arrives too late and you trip.
• "A longer, faster rope makes doubles easier." Rope fit matters more than length. Size it so the handles reach your armpits when you stand on the middle, and a lightly weighted or stiff cable gives feedback that helps timing. A too-long rope drags on the floor and a whippy one is hard to feel.

Related terms

Double-under FAQ

What is a double-under in simple terms?

A double-under is a jump rope rep where the rope passes under your feet twice in one jump instead of once. You jump slightly higher than normal and spin the rope faster with your wrists. In CrossFit each double-under counts as a single rep.

How is a double-under different from a single-under?

In a single-under the rope passes under your feet once per jump; in a double-under it passes twice. The double-under needs a slightly higher, stiffer jump, a faster wrist rotation, and precise timing, which makes it far harder to learn even though the jump itself is similar.

Why can't I do double-unders even though I'm fit?

Double-unders are a timing and coordination skill, not just a fitness test. Many strong, fit athletes fail early attempts because the fast double wrist-snap has to sync with a single jump. The skill usually clicks suddenly once that pattern clocks in, so practice fresh and often.

How high should I jump for double-unders?

Only slightly higher than a single-under, roughly 5 to 15 centimeters off the floor. Jumping too high forces you to pike at the hips or tuck the knees, which shortens hang time. The rope clears twice because your wrists spin it faster, not because you stay airborne longer.

What drills help me learn double-unders fastest?

Start with unbroken single-unders, then power jumps without a rope, then penguin taps (two quick thigh taps per jump), then the 3-1 drill: three big single-unders into one double-under. This layers the fast wrist rotation onto a familiar jump and is the quickest bridge to your first rep.

Where should my hands be during double-unders?

Keep your hands just in front of your hips, a little wider than your body, with your elbows tucked to your ribs. Spin the rope with small, fast wrist circles. Raising the hands as you tire shrinks the rope loop and is a common cause of trips late in a set.

How many single-unders should I do before trying doubles?

Aim to string together at least 40 to 50 unbroken single-unders with quiet arms and a relaxed grip before attempting double-unders. That proves you own the rhythm, the ankle bounce, and the wrist mechanics the double-under is built on, so you learn timing rather than the basics.

Why does the rope keep hitting my feet or shins?

Usually the rope arc is too slow because you are swinging from the arms, or the loop shrinks because your hands drift up as you fatigue. Pin the elbows, spin from the wrists, and keep the hands low. Whipping your feet up by tucking the knees also causes late trips.

How do I scale double-unders in a workout?

If you cannot do double-unders yet, substitute single-unders, commonly at a 2-to-1 or 3-to-1 ratio, to keep your heart rate up. If your double-unders break under fatigue, do smaller unbroken sets with short rests rather than grinding through repeated trips.

What size jump rope is best for double-unders?

Size the rope so the handles reach about your armpits when you stand on the middle of the cable. A lightly weighted or stiff speed cable gives feedback that makes the timing easier to feel. Ropes that are too long drag on the floor, and very whippy ones are hard to control.

References

1. From Single-Unders to Double-Unders (jump rope progression). CrossFit.com Essentials
2. Jump Rope Training Improves Muscular Strength and Cardiovascular Fitness in University Students: A Controlled Educational Intervention. PMC, 2024
3. Rope skipping increases bone mineral density at calcanei of pubertal girls in Hong Kong: A quasi-experimental investigation. PLOS One, 2017. PMC5722366
4. What Are Double Unders & How To Do Them. Crossrope
5. Double Unders For Beginners: A 7 Step Progression To Mastery. WODprep
6. Master the Jump Rope Again with Double Unders. BarBend
7. How To Do Double Unders. PureGym Exercise Library