Single unders are the base for double unders and every rope workout. Find rope length, wrists and rhythm, with milestones up to 100 jumps in a row.
Single unders are basic jump rope: the rope passes under your feet once per jump. They are the foundation for double unders, rope intervals and every workout that says "100 single unders".
The honest answer to "does it do anything?": yes, with a caveat. A meta-analysis of 21 studies with 1,021 participants found small to moderate improvements from jump rope training in resting heart rate, endurance, jumping, sprinting and range of motion, with effect sizes between 0.23 and 1.19 [1]. The catch: 18 of the 21 studies were done with people under 18 and lasted 6 to 40 weeks. For adults in everyday CrossFit it is a hint, not proof.
You usually learn the basic form in one session; a smooth rhythm over 50 to 100 jumps often takes weeks (experience, not study data).
Stand with both feet on the middle of the rope. Pull the handles up. If they reach your armpits, the length is right. If they only reach your hips, the rope is too long; shorten it.
Milestone: the rope does not drag on the floor and is not too long.
Keep your elbows close to your body, hands about hip height slightly away from you. Turn the rope from the wrists only, small circles, no arm swinging. The shoulders stay calm.
Milestone: turn evenly for 30 seconds, elbows at your sides.
Make small jumps on the balls of your feet, only a few centimeters high. Keep the knees soft and the landing quiet. The higher you jump, the more time you need – and the more tired you get.
Milestone: jump calmly for 30 seconds, quiet landing.
Now the rope comes in. Jump exactly when the rope passes under you. Start slowly. A measurement of 22 healthy women aged 18 to 25 showed that at an easy pace (105 skips per minute) the landing load was lower than in running but higher than in walking [2] – so easy pace is not a rest program, but not a pounding program either.
Milestone: 10 jumps in a row without catching the rope.
Progress in steps: 20, 50, 100 in a row. Look straight ahead and breathe evenly. If you tense up while jumping, pause briefly and go back to turning from the wrists.
Milestone: 100 single unders in a row. Then you are ready for double unders.
On planning: start every session with two or three minutes of easy single unders as a warm-up for calves and ankles (practice, not study data). If a workout shows 100 or 150 single unders, split them into blocks of 25 to 50 instead of pushing until you catch the rope – a miss costs more time than a short breather.
Single unders are one of the least dangerous movements in CrossFit, but at high rep counts they load the calf, Achilles tendon and the sole of the foot. Build up your jump count over weeks, not in one day. If you want long sets of 200 to 300 jumps, first manage a clean 100 without your calves hurting (practice, not study data).
Jump on a floor that gives slightly, not on concrete. Stop if the foot, Achilles tendon or shin stabs. This guide explains and motivates but does not replace supervised training.
Do the side swing as a bridge to double unders: swing the rope sideways at the hip without jumping, then alternate between a jump and a side swing. That teaches you to lead the rope instead of chasing it. And do not tell yourself "turn the wrists", tell yourself "drag the rope along the floor" – a picture from the outside. According to the meta-analysis on attentional focus, such external cues help learning and retention [3].
Stand on the middle with both feet and pull the handles up: they should reach your armpits. That is a practice standard, not a study figure. If the rope is too long it drags; if it is too short you catch it.
The basic form often works after one session. A round rhythm over 100 jumps usually takes a few weeks with two to three short sessions per week (experience).
At an easy pace (105 skips per minute), joint loads in 22 young women were lower than in running but higher than in walking [2]. So well dosed it is a sensible endurance exercise, but no free pass for hundreds of jumps on day one.
Yes, as a rule of thumb: 100 single unders in a row before you start double unders. The rhythm and the wrist turn are the same, only the speed increases.
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