Copenhagen plank: a side plank with your top leg on a bench, and what the studies measured

A Copenhagen plank is a side plank with a twist in the setup: your top leg rests on a bench and your bottom leg hangs free, so the inner thigh of the top leg, the adductors, has to hold your hips up. The sides of your trunk work as they do in any side plank. The name comes from the Copenhagen adduction exercise, which one study calls a dynamic exercise; the plank is a held version of it.

It's a hard hold. In a study of ten plank variations, the plain side plank got the lowest effort rating and a long-lever Copenhagen version the highest.¹ This page covers the setup, the short and long lever versions, the faults, what the studies measured, and the sets.

How to do a Copenhagen plank

1. Lie on your side next to a flat bench, elbow directly under your shoulder, forearm on the floor.
2. Put your top leg on the bench. For the short lever, rest the inside of the knee on it; for the long lever, rest the inside of the ankle or foot on it.
3. Lift your hips by pressing the top leg down into the bench and your forearm into the floor, until your body is one straight line from head to feet.
4. Let the bottom leg hang under the bench, or lift it up to meet the bench to make it harder.
5. Hold, breathing steadily, then lower your hips. Rest, then switch sides.

A padded bench or a folded towel under the knee or ankle helps. These cues are practical, not study findings.

Short lever, long lever, and harder

The further the bench is from your hip, the more your inner thigh has to hold. A study measured it: in 48 field-sport athletes doing an isometric Copenhagen adduction, the hip adduction torque, the turning force the inner thigh produced, was greater in the long-lever position than the mid-lever, and greater in the mid than the short. Adding a weight of 10% or 20% of body weight raised it too, and that effect was consistent across the lever lengths.²

In the ten-variation study, the long-lever and elevated Copenhagen versions brought greater oblique activity and higher effort ratings.¹ If you can't hold the short lever for about ten seconds, build the side plank first. That threshold is practical, not from a study.

The common faults, and a fix for each

• Hips sagging. The bottom hip drops toward the floor. End the hold, or go back to the short lever.
• Hips piking up or rolling. Keep one straight line and your chest facing forward.
• Holding with the shoulder. Push the floor away; don't sink into the elbow.

What the studies measured

The faults and fixes above are practical. Most of the research is on the Copenhagen adduction exercise, moving or held. Each study below is a lab measurement or one short training study:

• The inner thighs, by modeled force. In 15 injury-free participants doing eight common inner-thigh exercises (squat, deadlift, sumo deadlift, step-up, lateral slide, lying leg lift and the short- and long-lever Copenhagen), muscle forces were estimated with a model built from movement, ground-force and muscle-activity recordings. The long-lever Copenhagen ranked in the top tier for every adductor muscle, and the short lever for two of them; the deadlift and sumo deadlift also reached the top tier for the gracilis and for the hip-straightening part of the adductor magnus, the biggest inner-thigh muscle.³ (The adduction machine page covers that muscle.)
• The inner thighs, by muscle activity. In 40 healthy male elite soccer players doing eight hip adduction exercises, peak activity in the adductor longus, an inner-thigh muscle, ranged from 14% to 108% of a maximal contraction across the exercises, and the authors called the Copenhagen adduction a dynamic high-intensity exercise. Activity in the glutes and abs was relatively low, 5 to 48%.⁴
• The obliques. In 15 recreationally active men, the internal oblique was the most active trunk muscle measured across ten side and Copenhagen plank variations, about 38 to 77% of a maximal contraction, and the Copenhagen versions brought greater and more one-sided oblique activity than the side planks.¹
• Strength over eight weeks. In 24 under-19 football players, those who added an eight-week progressive Copenhagen adduction program to their usual training gained 35.7% in eccentric hip adduction strength (the inner thigh resisting while it lengthens) and 20.3% in eccentric hip abduction strength; the group that trained as usual didn't change.⁵

Read together: in these mostly small studies, the Copenhagen plank loaded the inner thighs in the top tier of the exercises tested, more with a longer lever, and one training study measured a strength gain. Modeled force and muscle activity aren't growth, and the one training study was in young football players.

Sets, holds and where it goes

• Two or three holds a side of 10 to 20 seconds on the short lever, each stopped when the line breaks, with about 30 seconds of rest. Move to the long lever when 20 seconds feels steady. These numbers are practical.
• At the end of a session, or on leg day after your squats and hinges, in place of the side plank in the "stop the lean" slot of the core block.
• Progress one thing at a time: longer holds, then the long lever, then the bottom leg raised. (Progressive overload covers the options.)

Common questions

What muscles does the Copenhagen plank work?

Mostly the inner thigh of the top leg, the adductors, with the obliques at the sides of your waist holding the line, as the studies above measured.^3,1

Copenhagen plank or the adduction machine?

Both train the inner thighs. The machine is seated and loads in plate steps; the Copenhagen plank needs only a bench and adds the side-plank job. The adduction machine page covers the machine.

What if my inner thigh or knee hurts?

If you have pain, an injury or a medical condition, a doctor or a physical therapist should set the limits before you train; this page is general guidance for healthy adults.

If you'd rather have the week planned

Holds are easy to list; deciding where they go in a week that already has squats, hinges and presses is the part a page can't do. Coaching is the version where your workouts live in Trainerize, built around the days and the equipment you actually have, and a weekly call looks at how the week went and sets the next one. Coaching to get stronger explains how that works, and apply is the first step. Otherwise: at the end of your next session, try two short-lever holds a side and write down the seconds.