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Plank Jacks

Plank jacks hold the upper body in a rigid plank while the feet jump out wide and back together like a horizontal jumping jack, hammering the trunk's ability to stay still under fast lower-body movement. They fit conditioning circuits for trainees who already own a solid static plank and want a cardio element added to it. Coached by Maddy (NASM-CPT) — these are the exact form cues he gives on every client's first week.

Muscles worked

Abs · rectus abdominis Deep core · transverse abdominis Obliques Lower back · erector spinae Front shoulders · anterior deltoid

Sets & reps by goal

Goal	Sets × Reps	Rest
Strength	5-6 fast intervals x 15-20 sec at max controlled speed	40-60 sec
Muscle	3-4 rounds x 30 sec steady	60 sec
Endurance	3 rounds x 45-60 sec continuous	30-45 sec

Level — Intermediate

Intermediate — requires a plank you can hold rigid while the legs move fast; regress to step-outs if the hips bounce.

Proper form — 5 cues

Lock in your plank first — elbows or hands under shoulders, glutes tight, one straight line.
Jump both feet out just past shoulder width, keeping the hip height unchanged.
Snap the feet back together with the same soft, quiet landing.
Brace the abs as if expecting a nudge — the torso must not bounce with the legs.
Set a metronome-steady rhythm you could hold for the entire timed round.

Breathing: Exhale on the jump out, inhale on the return, keeping the breath as rhythmic as the feet.

The 3 mistakes Maddy corrects most

Hips bob up and down with every jump.. The bounce means the trunk is riding the legs' momentum instead of resisting it, which deletes the anti-movement training you came for. Fix: Slow the jump rate and imagine your hips sliding along a fixed rail — if the bobbing continues, regress to alternating single-leg step-outs.

Feet jump too wide.. An extreme straddle drags the hips down, over-arches the lower back, and makes the return jump progressively sloppier. Fix: Limit the width to just outside the shoulders — the challenge should come from tempo and trunk stillness, not from straddle distance.

Shoulders drift back behind the hands as fatigue builds.. Sinking backward unloads the shoulders and serratus, letting the plank collapse from the top down. Fix: Keep the shoulders stacked directly over the wrists or elbows, and end the round when you can no longer hold them there.

Common questions

Are plank jacks cardio or core work?

Both, which is exactly their value in a circuit. The legs jumping in and out drives your heart rate up like any jack variation, while the trunk works isometrically the entire time to stop the hips bouncing and the back arching. If your plank line collapses, though, they become neither — form decides which benefits you actually collect.

Can I do plank jacks on my elbows instead of my hands?

Yes — the forearm version is often the better choice. It takes the wrists out of the impact equation and lowers your centre slightly, which makes the trunk work more honest. The hand version adds shoulder stabilisation demand. Both are legitimate; pick forearms if your wrists complain, hands if you want the extra shoulder challenge.

How long should a set of plank jacks last?

Only as long as the plank stays rigid. For most people that is 20 to 40 seconds of continuous jumping; conditioned trainees can push toward a minute. Programming three to four such rounds inside a circuit works well. The moment hips start bobbing or landings get loud, the useful part of the set is over — rest and reset.

Related exercises

Alternate Hand Extension in High PlankAbs · Deep core Inchworm to Low to High PlankAbs · Deep core Inchworm to Shoulder TapsAbs · Deep core Palm to Finger PlankAbs · Deep core Tapping Finger PlankAbs · Deep core

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