The Copenhagen plank is brutally hard, looks slightly ridiculous, and is one of the most respected adductor exercises in sports performance — largely because groin strains are common and this is one of the few things that reliably builds the tissue that suffers them. Here's the honest guide. The Copenhagen plank is a side plank with your top leg supported on a bench, loading the adductors of that leg — and it's valued in sport specifically for building groin strength and reducing strain risk.
What the Copenhagen plank trains (the honest mechanics)
It's a side plank variation where your top leg rests on a bench or box and your bottom leg hangs free, so the adductors of the top leg have to work hard to hold your body up. It trains those inner-thigh muscles eccentrically and isometrically under significant load — which matters, because that's closer to how they get injured (lengthening under tension during lateral movement) than any machine adduction exercise. You also get substantial lateral core and hip stability work as a bonus. It's the strength counterpart to the mobility work in the adductor stretch guide.
Why athletes care about it (the honest case)
Groin strains are one of the more common injuries in sports involving sprinting, kicking, and rapid change of direction — soccer, hockey, court sports. The Copenhagen plank has become a staple in athletic programmes because adductor strengthening programmes have been associated with reduced groin injury rates in the research literature, and this exercise loads the adductors particularly well. The practical logic is the same as any injury-prevention story: tissue that's strong enough for the demands placed on it tolerates those demands better. If you play a sport with a lot of lateral work, this is one of the highest-value exercises you can add.
How to do it (and how to scale it)
Almost nobody should start with the full version. Level 1 — short lever: lie on your side and place your top knee (not foot) on the bench, bottom leg on the floor. Lift your hips so your body forms a straight line, supporting on your forearm. Hold. Level 2 — short lever, bottom leg raised: same, but lift the bottom leg to meet the top. Level 3 — long lever: top foot on the bench (much harder, longer lever arm), bottom leg hanging.
Level 4 — full Copenhagen: top foot on bench, bottom leg lifted to meet it, body in a straight line. Start at 10–20 second holds and build. Progress a level only when the current one is comfortable for 30+ seconds.
The too-much-too-soon sin (this one bites)
Honest warning: the Copenhagen plank produces significant muscle soreness in the adductors, and jumping to the full version is a reliable way to be limping for several days. The adductors are also strain-prone tissue, which makes aggressive introduction genuinely unwise rather than just uncomfortable. The fix: start at level 1, hold for short durations, and build over weeks — not sessions. Two sessions a week is plenty. Expect noticeable DOMS after your first exposure regardless of how conservative you were; that's normal, and the second week is far kinder. Ease in and it becomes a sustainable staple; rush it and you'll abandon it.
Form details that matter
A few points that determine whether it works. Keep your body in a straight line from head to feet — don't let your hips sag toward the floor or pike upward. Keep your supporting shoulder stacked over your elbow, and press through the forearm rather than collapsing into the shoulder. Keep your top leg actively pressing down into the bench — that active squeeze is where the adductor work comes from. And breathe rather than holding your breath through the set. If your hips are dropping or your form is degrading, end the set — time under quality tension is the goal, not surviving an arbitrary duration.
Where it fits (pair accordingly)
Use the Copenhagen plank twice a week as an accessory — 2–3 sets per side, holding to quality rather than failure. Pair it with hip abduction work for the opposing outer-hip muscles (balance matters), adductor mobility, and single-leg strength like the Bulgarian split squat. It fits especially well for athletes doing change-of-direction work and court or field sport. Progress with time under tension, then by advancing the lever length — a form of progressive overload that doesn't need added weight.
Quick answers
What does the Copenhagen plank work?
The adductors (inner thigh) of the top leg, plus lateral core and hip stability.
Why is it good for groin injury prevention?
Adductor strengthening programmes are associated with reduced groin injury rates, and this loads the adductors particularly well.
How do I scale it?
Start with your top knee on the bench (short lever) rather than your foot, and keep the bottom leg on the floor.
How long should I hold it?
Start with 10–20 seconds and build; progress the level once you're comfortable at 30+ seconds.
How often should I do it?
Twice a week is plenty — it's demanding and produces significant soreness.
Why am I so sore after?
The adductors are rarely trained this way — expect DOMS after the first exposure; it settles quickly.
Do I need a bench?
A bench, box, chair, or couch all work.
Groin strains happen to muscles that weren't strong enough for what was asked of them. The Copenhagen plank is the least glamorous, most effective answer to that.
The Copenhagen plank is the gold-standard adductor exercise for athletes — hard, unglamorous, and genuinely associated with reduced groin injury risk. Start with your knee on the bench rather than your foot, hold for short durations, and progress the lever length over weeks. Twice a week, paired with abductor work and mobility, and you've covered a common injury most people never train for.