Copenhagen Plank: How to Do It, Muscles Worked and Progressions

The Copenhagen plank is a side plank with your top leg resting on a bench and your bottom leg hanging in the air, and it is the single best groin exercise most people have never done. It came out of research at the University of Copenhagen into why football players kept tearing adductors, and it has since become standard in professional football and Gaelic games. The move looks simple. It is not. Anyone who has held one for 20 seconds knows the inside of the thigh can cramp in ways no other exercise manages.

How to do a Copenhagen plank

You need a bench, a box or a sofa arm at roughly knee height. Set up on the floor beside it, at right angles.

1. Get into position. Lie on your side with your bottom forearm on the floor, elbow directly under your shoulder. Rest your top leg on the bench so the inside of your ankle and lower shin sit on the surface, not the outside of your foot.
2. Set the lower leg. For the full version, hold your bottom leg off the floor and slightly behind or below the top leg. For the beginner version, leave the bottom foot planted on the ground and take some weight through it.
3. Lift. Squeeze the top inner thigh and press down into the bench to drive your hips up until your body makes a straight line from ankle to shoulder. Your hips should not sag and they should not pike up either.
4. Hold, then lower under control. Keep breathing. Lower slowly rather than dropping, because the eccentric part is where a lot of the protective adaptation happens.
5. Swap sides. Do the same number of holds or reps each side, even if one side is obviously weaker. The weaker side is the reason you are doing this.

Muscles worked

• Adductor longus, brevis and magnus (top leg). These are the target. They pull the thigh toward the midline, and in the Copenhagen they do it against your entire bodyweight while lengthened, which is the loading pattern that builds resilient tissue.
• Gracilis and pectineus. The smaller inner-thigh muscles chip in, and the gracilis crosses the knee, so it takes some of the load through the whole range.
• Obliques and quadratus lumborum (bottom side). They stop your hips folding toward the floor. This is why the Copenhagen doubles as a serious lateral core exercise.
• Glute medius and shoulder stabilisers. The bottom hip and the propping shoulder both work isometrically to keep you square.

An RCT on under-17 footballers found eight weeks of the Copenhagen adduction exercise changed the actual architecture of the adductors, with increases in muscle thickness and fascicle length (adductor architecture RCT). Longer fascicles matter because muscles that can produce force at long lengths tend to strain less.

Why it beats a hip adduction machine

Two reasons, and neither is about the muscle being "activated more". First, the loading is eccentric and at length, so you are strong precisely where groin strains occur rather than in a comfortable mid-range. Second, it costs nothing and needs no machine, which means people actually keep doing it.

The evidence behind that is unusually good for a single exercise. Harøy and colleagues cluster-randomised 35 semi-professional Norwegian football teams into an adductor programme built around this movement or normal training. Over the season, groin problem prevalence was 13.5 percent in the intervention group against 21.3 percent in the control group, a 41 percent lower risk (Br J Sports Med, 2019). Almost nothing else in injury prevention research posts numbers like that off one exercise.

If you play football, hockey, rugby or anything with hard changes of direction, this belongs in your week. The NHS already asks adults for muscle-strengthening work covering all the major muscle groups on at least two days a week, and the adductors are the group nearly everyone skips.

Progressions, easiest to hardest

• Short-lever hold, bottom foot down. Top knee bent and resting on the bench, bottom foot planted. Hold 10 to 20 seconds. Start here even if you think you are strong; the soreness the day after will explain why.
• Short-lever hold, bottom leg lifted. Same bent top knee, but the bottom leg floats. This is where most people should live for the first month.
• Long-lever hold. Top leg straight, ankle on the bench, bottom leg in the air. The classic version, and much harder than the bent-knee variant because the load sits further from the hip.
• Long-lever reps. Instead of holding, lower your hip until it lightly touches the floor and drive back up. Six to ten controlled reps a side beats a long shaky hold.
• Weighted or feet-elevated. Add a light ankle weight or put the bottom foot on a low box so the hip travels further. Only worth it once you can do 10 clean long-lever reps a side.

A plyo box or a weight bench makes the height easy to standardise, and a set of ankle weights is the simplest way to load it once bodyweight stops being enough.

Common mistakes

Rolling backwards. The hips drift behind the shoulders and the exercise turns into an awkward half-twist. Stack your shoulders, hips and ankles in one plane, as if you were pressed against a wall.

Sagging hips. If the hip drops as you hold, the adductor has already given up and you are hanging on the shoulder. Stop the set. Quality here beats duration by a wide margin.

Foot on the bench instead of the shin. Balancing on the outside edge of the foot makes the whole thing wobbly and puts the ankle in a bad spot. Get the inside of the shin and ankle flat on the surface.

Going straight to the full version. This is the big one. Jumping to the long-lever hold on day one is the fastest route to a genuinely sore groin that keeps you out of the gym for a week, which rather defeats the point of an injury prevention exercise.

Skipping the weaker side. People quietly do fewer reps on the side that hurts. Match the sets, and if the difference is large, do an extra set on the weak side for a few weeks.

Sets and reps

• Building it: 3 sets of 10 to 15 second holds each side, twice a week, on the short-lever version.
• Strength: 3 sets of 6 to 10 long-lever reps each side, twice a week. Rest 45 to 60 seconds.
• In season, maintaining: 2 sets of 30 second holds each side, once a week.

Put it at the end of a lower-body session or after a warm-up, not before heavy squatting, because tired adductors change how you brace. Expect real soreness the first two or three sessions, then it settles quickly. Pair it with glute bridges and a side plank if you want a short, complete hip and trunk block.

Recommended reads

1. How to do a side plank
2. Glute bridge technique and progressions
3. The best plyo boxes in the UK
4. The best weight bench in the UK
5. Hip flexor stretches that actually work