Mountain climbers: a plank that moves, done slow for your core or fast for your lungs

A mountain climber is a plank that moves. You hold a high plank on your hands and drive one knee toward your chest, put that foot back, and drive the other. Done slowly, one knee at a time with a pause, it's a core exercise: the plank has to stay still while a leg moves under it. Done fast, the legs switching in the air, it's conditioning, and that's how most workouts use it.

This page covers the setup, the slow and fast versions, what the exercise works, what the interval studies that used it found, the faults, and the sets. The hold it starts from is on how to do a plank.

How to do mountain climbers

1. Start in a high plank: hands flat under your shoulders, arms straight, legs straight behind you, up on your toes.
2. Make one straight line from your head to your heels. Brace your midsection and squeeze your glutes so your hips don't sag.
3. Drive one knee toward your chest without letting your hips rise or your back round.
4. Put that foot back where it started.
5. Drive the other knee. That's one rep per side.
6. For the fast version, switch legs in the air, one foot landing as the other leaves, and keep your shoulders over your hands.

Slow or fast: two different exercises

• Slow mountain climbers are a core exercise. Drive the knee in, pause for a second, put it back. The job is to keep the plank still while your weight shifts to three points. Ten slow reps per side is a hard set.
• Fast mountain climbers are conditioning. The legs alternate quickly, and the work is in your heart and lungs. They belong in timed rounds, like burpees.
• Cross-body mountain climbers drive each knee toward the opposite elbow, which adds a turn through the trunk. Keep the turn small and the hips level.
• Easier: hands on a bench or a sturdy box. The higher the surface, the less of your weight is on your hands.
• Harder: feet on sliders or a towel on a smooth floor, so each leg slides in and out instead of stepping.

What mountain climbers work

The plank part asks the front of your trunk to hold the line, the job the plank page covers. Your shoulders and arms hold you up the whole time, and the muscles at the front of your hips pull each knee in. Fast, the whole thing becomes work for your heart and lungs.

That's a description of the movement, not a measurement: a PubMed search for this page found no study that measured muscle activity in the floor mountain climber itself (one Pilates study measured a chair-based exercise with the same name). The studies below used it inside interval workouts, mixed with other moves, so they say what those workouts did, not what the mountain climber did on its own.

What the interval studies found

• Four weeks of 20-second rounds. In 22 recreationally active women, one group trained four days a week for four weeks with one set of eight 20-second rounds of a single exercise, burpees, jumping jacks, mountain climbers or squat thrusts, with 10 seconds of rest between rounds. Aerobic fitness (peak oxygen uptake) rose about 8%, in line with the about 7% of a group doing 30 minutes on a treadmill, and the interval group also improved its muscular endurance, push-ups by 135% and sit-ups by 64%.¹
• Six weeks against running. In 25 active, healthy adults, one group did 20 rounds of 30 seconds all-out with 30 seconds of rest, using jumping jacks, mountain climbers, burpees and squat jumps, three times a week for six weeks; the other ran continuously for 20 minutes at 80% of maximum heart rate. The interval group's push-ups improved more. Muscle thickness in the arms and legs didn't change significantly in either group.²
• As hard as rowing intervals. In 22 healthy, active adults, six rounds of about a minute each of push-ups, jump squats, mountain climbers and air squats, done as fast as possible with 75 seconds of recovery, reached 92 to 96% of maximum heart rate, as rowing intervals did. Peak heart rate was a little higher in the bodyweight session, 174 against 167 beats a minute.³
• One session, measured. In 20 healthy young men doing one all-out session of 20 rounds of 30 seconds with 30 seconds of rest, using jumping jacks, mountain climbers, burpees and squat jumps, blood lactate, a marker of hard effort, rose from about 1 to about 14 mmol/L. The authors classed the session as high intensity.⁴

Read together: fast mountain climbers belong to the same family as burpees, a bodyweight way to make interval training hard. The training trials were short, four to six weeks, and small, and none can separate the mountain climber from the rest of the circuit.

The common faults, and a fix for each

• Hips piked up. Your body turns into a tent and the knees have an easy path. Lower your hips until shoulders, hips and heels line up.
• Hips sagging. Brace and squeeze your glutes; if the line won't hold, slow down.
• Shoulders behind your hands. Keep them stacked over your hands; rocking back shortens the plank.
• Tapping, not driving. Fast feet that barely move are a jog in place. Bring each knee well under your hips.
• Bouncing your hips side to side. In the fast version a little movement is normal; a big swing means the pace is ahead of your plank.
• Pushing through something that hurts. Burning shoulders in a long round are normal; a sharp or lasting hurt in a wrist or a shoulder isn't. Stop, and see a doctor or a physical therapist.

Sets, rounds and where they go

• Slow, in a core block: two or three sets of 8 to 10 per side with a pause, at the end of a session. They fit the plank slot in the core workout on days you want a moving version.
• Fast, as a finisher: eight rounds of 20 seconds on and 10 seconds off, alone or alternating with burpees.
• In a bodyweight circuit: 30 to 60 seconds, with jumping jacks, squat jumps and burpees, and a short rest between.
• After your lifting, not before it. Cardio and lifting covers the order.

Progress the slow version by adding a pause or sliders, and the fast version by adding rounds before you add speed.

If you'd rather not plan it alone

Mountain climbers fit almost anywhere; deciding where they go in a week that already holds lifting and everything else is the part a page can't do. Coaching is the version where your workouts are built around the days you actually have, and a weekly call looks at the week you just had and rebuilds the next one. Coaching for a week that doesn't hold still explains how that works, and here's how to apply. Otherwise: end your next session with three slow sets of eight per side, and stop each set when your hips start to rise.