Mountain Climber
A forearm plank where you drive one knee at a time up to your upper arm. Your torso stays put while your legs do the work — the next step once a plank has got easy.
The mountain climber needs nothing but floor space. That's why it works in the studio and in a hotel room alike, and why it turns up in almost every plan.
What makes it useful is the feedback built into it: only the slight pelvic tuck that brings your ribs and pelvis together lets the knee reach your upper arm. So the exercise tells you whether the position is right. Done slowly and cleanly, it stays demanding for years.
Starting position
Forearm plank on the floor or a mat. Elbows directly under your shoulders, legs straight, feet hip-width apart. Stay tight through the whole body.
The three cues
- Forearm plank — shoulders stacked over your elbows, whole body tight
- Tuck your pelvis slightly until your ribs and pelvis come closer together — your abs are working now
- Drive one knee at a time up to your upper arm
Common faults
| Fault | How to fix it |
|---|---|
| Your knee only makes it halfway | Take it all the way to your upper arm. If you can't get there, you're not tucking the pelvis — reset the position and do fewer reps. |
| Your hips drift upward | Keep your ribs and pelvis close together. Once your hips rise, your abs stop working and you're just moving your legs. |
| Your lower back sags and arches | End the set. Four clean reps beat ten with a collapsed position. |
| Too fast | Slow down. This one is about controlling the position, not about speed. |
Variations
| Variation | When to use it |
|---|---|
| Holding a forearm plank | 30 seconds, ideally a minute, cleanly — until you can do that, the mountain climber isn't worth doing |
| Mountain climber from the forearm plank | What we do in the studio: one knee at a time up to your upper arm |
| Slow tempo with a brief pause at the top | Your position is solid and you want more control rather than more reps |
| Mountain climber with no kit at all | Hotel, holiday, nothing to train with — which is why this exercise is in the plan in the first place |
Reps and load
First you need a plain forearm plank: 30 seconds, ideally a minute. From there you start at 4 to 6 reps, spread over several sets across the session. Work up to at least 20 a session. Early on, do only as many as you can keep clean — if this is new to you, it gets hard fast.
Which muscles do the work
| Muscle | Role | What it does here |
|---|---|---|
| Rectus abdominis M. rectus abdominis | Prime mover | Keeps the ribcage stacked over the pelvis; decelerates the leg on the way back |
| Hip flexors M. iliopsoas, M. rectus femoris | Prime mover | Draw the knee up towards the upper arm |
| Transverse abdominis M. transversus abdominis | Stabiliser | Holds tension through the trunk while the legs move |
| Obliques Mm. obliqui | Stabiliser | Stop the pelvis rotating as the knee comes in |
| Serratus anterior M. serratus anterior | Stabiliser | Keeps the shoulder blade on the ribcage — otherwise you sink between your shoulder blades |
| Chest and triceps M. pectoralis major, M. triceps brachii | Stabiliser | Hold the upper body up in the plank position |
| Glutes M. gluteus maximus | Stabiliser | Extend the hip of the back leg, keeping the body in one line |
The stimulus isn't the knee coming in — it's what the trunk has to stop while the knee moves: the pelvis tipping or twisting. That's why slowing it down makes it harder, not easier.
Explained in full
Why touching your upper arm is the part that decides everything, what happens when your hips drift up, and how many reps my clients actually start with. · 3:18
Seeing it done right is not the same as doing it right
Video, cues and variations take you a long way. What they cannot give you is an outside eye at the moment the movement isn't quite there yet. That is what training with me is for — in the studio or in a workshop.
See the workshopsNew exercise pages are added all the time — the newsletter keeps you posted.
Sources
McGill SM, Karpowicz A. (2009). Arch Phys Med Rehabil 90(1):118–126. DOI: 10.1016/j.apmr.2008.06.026 — Moving the limbs while the trunk stays braced raises muscle activation (n = 8; curl-up, side bridge and bird dog — not the mountain climber; the principle is carried over). (Evidence type: EMG)
McGill SM. (2001). Exerc Sport Sci Rev 29(1):26–31. DOI: 10.1097/00003677-200101000-00006 — Lumbar stability comes from the whole trunk musculature working together rather than from any single muscle — a conceptual reference, not a measurement. (Evidence type: Review)
Ekstrom RA, Donatelli RA, Carp KC. (2007). J Orthop Sports Phys Ther 37(12):754–762. DOI: 10.2519/jospt.2007.2471 — The prone bridge stays below 45% of maximum voluntary contraction — a stability and endurance stimulus rather than a strength stimulus (n = 30, healthy participants). (Evidence type: EMG)
A note on context: EMG studies show which muscles an exercise recruits — that is a good reason to pick it, but it does not replace adjusting things to the person in front of you. See a doctor for persistent or severe pain.