The Copenhagen Plank, or the Copenhagen Side Plank, is a side plank variation that, in addition to training the abdominals, targets the adductor (groin) muscles. As such, a better name might be the adductor plank, or adductor side plank, but the Copenhagen name has stuck.
You set up a Copenhagen plank like a side plank, except you place your top foot on a bench while hovering your bottom foot in the air. This requires the adductor muscles to contract isometrically.
Obviously, this trains the adductor muscles. So your next question might be why you should train them in the first place.
Think of these inner thigh muscles like the hamstrings of the frontal plane. They’re one of the major muscle groups that help us move side to side. If you’re an athlete, then, they’re a crucial part of most sports.
More broadly, you may think of the adductors as crucial stabilizer and “core” muscles. Anytime you’re standing on one leg (like every step you take while walking) the adductors work to prevent your knee from caving in. Just like the abdominal muscles, they often work in everyday life as stabilizers, not necessarily movers. The Copenhagen plank trains them in this fashion, and therefore has more transfer towards actual real life than exercises like the adductor machine.
As I’ve learned from the postural restoration institute, a lot of the movements in our body couple together. On exhales, our body moves towards flexion and internal rotation. Simply, when our abdominals contract, our adductors are primed to contract also. By strengthening one muscle group, we help shift into the posture that allows the other to contract as well, creating a positive feedback loop. Strong adductors means stronger abs and vice versa, and both help us shift out of the extended posture that most of us live in.
The adductors make up one of the biggest muscle groups in your lower body. Training them effectively, like training all other muscles, will improve their form as well as their function. I don’t need to say much else here because every bodybuilder in history has trained the inner thighs, so obviously there’s something to it.
1) Set up with your head perpendicular to a bench and facing away.
2) Plant your elbow and forearm parallel to the bench
3) Place your front leg on the bench
4) Lift up your hips so you’re in a straight line from the ankles to the shoulders
5) Take a deep exhale and engage your abs and glutes. This will improve abdominal and adductor activation.
6) Lift your bottom leg up so it’s parallel to the ground.
7) Hold for 2-4 slow breaths, aiming for 7-10 second exhales.
8) Switch sides and repeat.
Aside from the main variation, there are several options to progress and regress the Copenhagen plank.
Instead of planting your ankle on top of the bench, if you plant you knee if will shorten the “lever,” as they say in physics, making it easier. This is great if you’re starting out and also if this bugs your knee (which we’ll get to) this option takes the knee out of the equation since it’ll be resting on the bench.
You can keep the bottom leg on the ground. All else equal I prefer this over the bent-knee variation because in real life the adductors contact with the ankle/foot as the contact point, so I think this transfers over to sports and real life better.
Planks aren’t that easy to add weight to. Fortunately, with side plank variations it’s not so difficult. If you’ve worked up to 4 breaths fo 10 seconds each side and you’re not feeling challenged, you can add some weight. With the top arm, grab a light dumbbell or kettlebell and hold it up in the air as you do so. This will create additional stability challenges, including challenging your shoulder stability like in a Turkish Get-Up. A kettlebell or dumbbell work fine, but for just like TGUs I find the kettlebell to work a little bit better. Here I’m using a DB because I’m using a home gym.
For even more stability challenges, move off of your forearm and onto your hand.
Far and away the most common complaint of this exercise is knee discomfort on the front leg. If that’s you, the first thing to ask is whether you were in a straight line (no hips sagging) with your abdominals engaged. If the answer is no, then you’re not ready for this exercise and should go back to regular side planks first until you’re stronger. In the meantime, you can strengthen your adductors with other isometric exercises.
If you’re coming off of a knee injury, or have a history of knee pain, try the regression variations first. Find the right variation that provides zero pain. If your form is otherwise great, but you still have knee pain, that’s a sign something might be off, and I would refer you to a physical therapist, athletic trainer, or other pain specialist.
Copenhagen planks can fit into a program where any abdominal or core exercise can go. Generally speaking, I think core exercise can be sprinkled in every training session during rest periods from major strength movements. This is called “active rest.”
This particular exercise you can do 1-2 times per week for 2-3 sets, and that will have you well on your toward stronger adductors, better posture, fewer injuries, and some compliments on your inner thighs.
For another fantastic ab exercise, check out the landmine rollout.