The Copenhagen Plank Works Double Duty as a Core and Inner-Thigh Exercise — Here’s How to Do It

These days, the fitness world is all about increasing efficiency. You perform compound movements to train multiple major muscle groups at once, do HIIT workouts to get your heart pumping and muscles shaking, and use circuits to structure your workouts so you don't get distracted between sets.

To get even more bang for your buck when it comes to strength training, turn to the Copenhagen plank, a side plank's leveled-up cousin that tests your core and lower-body strength. Ahead, learn details on all the benefits a Copenhagen plank has to offer and find out how to do one with perfect form every single time — no matter how you modify or spice up the move. Promise, a little bit goes a long way with this bodyweight exercise.

How to Do a Copenhagen Plank

Just like the side plank, the Copenhagen plank involves lying on one side of your body with your bottom elbow bent, forearm resting flat on the floor, and legs fully extended. But instead of stacking or staggering your feet on the floor, you’ll prop one foot on top of a bench (or couch, chair, or another stable surface that's about 18 inches tall). Then, you'll hover the other foot a few inches below the bench and hold this position as steadily as possible.

“If done correctly and you’re really focusing on what it's targeting [read: the core and thighs], the Copenhagen plank is really hard to hold for even 10 good seconds,” says Analisse Ríos, C.S.C.S., a certified personal trainer and strength and conditioning specialist in Connecticut. “It doesn't just target your obliques like a side plank, but it also fires up your adductors and your abductors — your inner and outer thigh muscles.” Sound complicated? Watch Ríos demonstrate the move below. 

A. Lie on left side of body with left elbow resting on the floor directly beneath left shoulder, both legs extended out to right side, and right arm extended toward ceiling. Place right foot on top of a bench and rest left toes gently on the floor.

B. Engage core, grounding through left elbow and side of left foot, and lift hips and knees off the floor.

C. Then, lift left foot off the ground so it's hovering a few inches below right foot. Gaze forward and maintain a straight line from head to heels. Hold this position.

The Key Copenhagen Plank Benefits

Based on the look of it, you can probably guess that the Copenhagen plank is a seriously challenging move. But what good does it actually do for you and your body? Here's the breakdown.

Strengthens Overlooked Leg Muscles

One of the primary benefits of the Copenhagen plank: It strengthens your hip abductors and adductors, muscles that are responsible for moving your leg away from or toward, respectively, the midline of your body, says Ríos. These muscles are called upon during lateral movements in your daily life (think: stepping to the side to avoid stomping on your pet, balancing on a subway car while it zooms forward). Your abductors also help stabilize your leg, preventing your knee from collapsing when you’re balancing on just one foot, she adds. 

And yet, “[the inner and outer thighs are] often neglected parts of the body, so some people have weak adductors without really knowing it,” she explains. “Then when they're moving laterally and going full speed [such as in sports], they pull their groin muscle, or they have super tight hip flexors.” What's more, the hip abductors and adductors both play a key role in stabilizing your pelvis, and if one of those muscle groups isn't strong enough to offer that essential support, you could develop lower back pain, Leigha VandenToorn, C.S.C.S., P.P.S.C., an NASM-certified personal trainer, previously told Shape. Regularly practicing Copenhagen planks, however, can strengthen these key lower-body muscles and help keep injuries at bay. 

Boosts Athleticism 

While holding the plank position, the stabilizer muscles in your core will need to work extra hard to keep your body — which is being supported only by the foot resting on the bench — in place. Plus, they'll be challenged to prevent you from rotating forward, says Ríos. And this training can do you some good: Improving your core stability not only helps prevent injuries in your back, but it can also improve your athletic performance, she notes. Say you’re a soccer player. You want to be able to plant your feet and quickly turn to move in the opposite direction of your opponent. “If you don’t have that stability and anti-rotation [capacity] in your core, your body would just continue going the way that it's going and you wouldn't be able to change directions super quickly,” says Ríos.  

Helps Correct Muscle Imbalances

The Copenhagen plank is a unilateral exercise, meaning it targets just one side of the body at a time. If you’re performing the exercise with your right arm on the floor, for example, you’ll fire up your right side’s obliques and left leg’s adductors and abductors, she adds. That’s why it can be particularly useful for finding — correcting — muscle imbalances, says Ríos. 

Say you notice that it’s much easier to do a Copenhagen plank on your right side than your left, a potential sign of a muscle imbalance. Serious imbalances can lead to compensated movement patterns and, in turn, an increased risk of injury, according to the American Council on Exercise. To even out that disparity and keep injuries at bay, you can temporarily prioritize Copenhagen planks on your left side, along with other strengthening exercises that target those weaker muscle groups.

Copenhagen Plank Muscles Worked

Along with your abductors, adductors, and hip flexors, the Copenhagen plank challenges practically every part of the core (which plays a key role in keeping your spine stable and safe), says Ríos. Still, your obliques, the muscles responsible for rotating your trunk, get a large chunk of the action. Plus, the exercise works your shoulder stability, particularly if you perform the exercise on your palm rather than your forearm, which reduces the surface area you’re balancing on, she adds. “As soon as you go up onto your palm instead of your forearm, you take away some of that stability, so there’s a little bit more work that your body has to do to stabilize and not rotate to one side,” she explains.

Copenhagen Plank Variations

Before you try any Copenhagen plank, it’s important to master the traditional side plank, which will help you build up the core strength necessary to tackle the challenging lower-body exercise, says Ríos. Once you’re ready to tackle the Copenhagen plank, try one of the modifications below and progress through other variations as you build up strength and stability. 

Modification: Copenhagen Plank with Short Lever

When it comes to the Copenhagen plank, the more surface area of your leg that rests on the bench, the easier the exercise will be, says Ríos. That’s why she usually starts her clients off with their top knee bent at a 90-degree angle and their knee and calf fully resting on the bench (aka a short lever), she says. As your adductors get stronger, slowly move more of your calf off the bench until just your foot is resting on it (the classic Copenhagen plank), she suggests.

Progression: Copenhagen Plank with Kettlebell or Knee Drive

Once the traditional Copenhagen plank feels like child’s play, up the ante by performing the exercise on your palm instead of your forearm. Or, try driving your bottom knee up so it's in line with your hips, keeping it bent at a 90-degree angle, suggests Ríos. “Now you're not only like working the adductors in the leg that's on top of the bench, but you're also using your hip flexors to bring the bottom leg [up to] 90 degrees,” she explains.

You can further challenge your shoulder stability and core’s anti-rotation capacity by holding a kettlebell with your free hand (with the bottom of the bell pointed toward the ceiling), extending your arm straight up, and holding it there. “That weight is trying to shift you forward and back, and you have to resist that rotation while holding yourself up with one leg,” she adds. Better yet, combine the two moves during a single set, as Ríos demonstrates below.

Along with those variations, you can also progress the Copenhagen plank by increasing the duration of the exercise. Start with 10 seconds, then, as the move becomes easier, slowly add a few more seconds at a time, says Ríos. “I wouldn't recommend more than 25 seconds or 10 slow breaths per side per set,” she adds. “There's no need to —  if you're doing it correctly, those are gonna be the longest 25 seconds of your life.”

Common Copenhagen Plank Mistakes

As you hold your Copenhagen plank, make sure to avoid rotating your shoulders forward, says Ríos. “That's the most common mistake you see in a Copenhagen plank because it's so hard to maintain that anti-rotation,” she explains. Imagine your heels, butt, and back of your head are all touching a wall and your body forms a straight line in order to get the most benefit out of the exercise, she suggests. If you notice your form is breaking down, consider scaling back to a modification. Most importantly, remember to breathe, says Ríos. “People hold often their breath because [this move] is so hard,” she adds. “I like to say ‘[hold the plank for] five breaths’ because that way people actually breathe.”

How to Add the Copenhagen Plank to Your Routine

While the Copenhagen plank can be an ideal exercise for optimizing lower-body strength and core stability, you should consult your health-care provider if you're experiencing any knee pain during the move, which may occur if you’ve had an injury or surgery on the arae in the past, says Ríos. But if you’re ache-free, continue mixing the Copenhagen plank into your routine — particularly if you’re a runner, she adds. “Every time you take a stride, you're essentially on the one leg,” she explains. “So building up the strength of those stabilizer muscles [in your legs and core] is important.” 

Ready to give the exercise a shot? Mix the Copenhagen plank into your usual resistance training regimen and try holding it for 10 to 20 seconds at a time, doing three to four sets on each side, suggests Ríos. And don’t let the difficulty level discourage you or make you feel inadequate — even pros like Ríos think the Copenhagen plank is an exhausting but worthwhile move. “It’s such a good exercise and I know I have to do it, but sometimes I'm like, ‘I just wanna do a side plank’ because I know how hard it is.”