Adductor Magnus Training: Seated Adductor Machine and Copenhagen Planks for Thigh Mass

Adductor magnus training is the missing piece for a lot of lifters who squat hard and still feel their legs look thin from the front. The short answer: squat deep, add 2-3 hard sets on the adductor machine, and use Copenhagen planks for groin strength. That stack covers size and resilience, though the evidence behind each piece is different, as we will see below. For the wider picture of leg training, see our complete guide to lower body and core training.

One thing first. You will see claims online that the adductor magnus is “the second largest muscle in the body.” I could not confirm that from the research, so I am not going to repeat it. You do not need the ranking to justify training it.

Why train adductors?

Most lifters skip them. Leg day becomes squats, leg press, curls and calves, and the inner thigh gets whatever is left over, which is usually nothing. Then they wonder why the leg looks narrow from the front.

The adductors sit on the inner thigh and pull the leg towards the midline. The adductor magnus is the biggest of the group, and part of it works like a hamstring, helping extend the hip.

That second job is why it gets hammered in squats and deadlifts. In an EMG-assisted modelling study of 15 injury-free people, the squat, step-up, deadlift and sumo deadlift all loaded the ischiocondylar part of the adductor magnus strongly (Collings et al., 2026). Hip-extension lifts, not just inner-thigh squeezes, are adductor lifts.

We cover the hip-angle mechanics in hip flexion depth and adductor magnus recruitment. Here the focus is practical training.

Do deep squats grow the adductors?

Yes, and depth seems to matter. In a randomized trial, 17 young men did either full or half squats twice a week for 10 weeks. MRI showed adductor volume rose 6.2% in the full squat group and 2.7% in the half squat group, a significant difference. Glute max followed the same pattern (6.7% versus 2.2%) (Kubo et al., 2019).

Caveats are real. It is only 17 people, all young men, and the groups were small (8 and 9). Still, a systematic review also concluded that full range of motion favours lower-body hypertrophy over partial range (Schoenfeld & Grgic, 2020). The practical read: if you only quarter-squat, you are leaving inner-thigh growth on the table. If depth bothers your knees or hips, our guide on squat depth for hypertrophy helps you pick a range you can own.

Does the seated adductor machine build thicker thighs?

Probably, with an honest asterisk: I found no trial that tested the adductor machine for muscle growth. The case is indirect. Hard sets taken close to failure through a decent range tend to grow muscle, and the machine makes that easy to do for the adductors without needing balance or skill.

What the machine does well is isolate. Squats spread effort across quads, glutes and adductors. The machine lets you add adductor volume without adding more hip and spinal fatigue. That makes it a decent stimulus-to-fatigue choice after heavy legs.

What it probably does not do: replace deep squats. The modelling study above did not test the machine, and the machine positions the hips in a seated, flexed position, so it likely favours the pubofemoral and inner-thigh parts more than the hip-extension part. That is my reasoning, not a measured result.

How to run it

1. Set the pads so your thighs start in a stretch you can control, not a painful one.
2. Sit tall, back against the pad, and squeeze in over about 1-2 seconds.
3. Pause briefly, then lower over 2-3 seconds. Do not let the stack slam.
4. Do 2-3 sets of 10-15 reps, stopping 1-2 reps short of failure. Our RIR and RPE calculator helps you judge that.
5. Add weight or a rep when you hit the top of the range for all sets.

What are Copenhagen planks good for?

A Copenhagen plank is a side plank with your top leg on a bench and your bottom leg off the floor. The top-side adductors hold your hips up.

In modelling, the long-lever version landed in the top force tier for every adductor muscle tested, which is why it sits at the hard end of the scale (Collings et al., 2026). In 40 elite football players, the Copenhagen adduction exercise and a banded hip adduction were the two dynamic high-intensity options, with adductor longus activity up to 108% of a maximal voluntary contraction in the top exercise (Serner et al., 2014).

Strength and injury results

Those results come from footballers, not bodybuilders, so keep that in mind.

• In 24 sub-elite U-19 players, 8 weeks of Copenhagen training raised eccentric hip adduction strength 35.7% versus no change in controls (Ishøi et al., 2016).
• In 45 elite U-19 players, swapping the Copenhagen exercise in for the Nordic hamstring exercise within the FIFA 11+ warm-up produced an 8.9% greater eccentric adduction strength gain than the standard programme (Harøy et al., 2017).
• In a cluster-randomised trial of 652 semiprofessional players, self-reported groin problems averaged 13.5% in the programme group versus 21.3% in controls, 41% lower odds of reporting groin problems (OR 0.59) (Harøy et al., 2019).

That last outcome was self-reported by questionnaire, and the trial could not blind players to the exercise. Keep the claim modest: it looks helpful for groin resilience in kicking and sprinting sports, and it is unlikely to hurt if you progress sensibly.

Can they add size?

Maybe. In 45 active adults, 8 weeks of Copenhagen training increased adductor muscle thickness on ultrasound by roughly 18%, but thickness went back to baseline after 4 weeks of detraining (Alonso-Fernandez et al., 2022). Ultrasound thickness is not MRI volume, and some of that swelling may be short-term. Use it as a strength tool that might also help size.

How do I put adductor magnus training into a week?

Think in three layers: a base, direct work, and resilience.

Piece	What	Starting dose	Why
Base	Deep squat or leg press	Your normal leg days	Loads adductor magnus as a hip extender
Direct	Seated adductor machine	2-3 sets of 10-15, twice a week	Easy extra volume, low fatigue
Resilience	Copenhagen plank (short lever first)	2-3 sets of 10-20 seconds per side	Strength and groin protection in sport

Drop the machine sets in at the end of a leg day. Do Copenhagen planks after your warm-up or on a second leg day, when you are fresh enough to hold good form. The leg plan on our free leg day workout shows where these fit, and programming a complete leg split covers weekly volume.

If you are on a home budget, a sofa-edge Copenhagen plank and deep goblet squats cost nothing. Banded adduction was also among the higher-intensity options in the EMG work, so a cheap loop band is a reasonable home option when you have no machine.

If you are short on time, here is the order of priority. Depth first, because it is free. Machine sets second, because they are cheap volume. Copenhagen planks third, because they need the most care and their evidence is mainly about strength and groin problems in sport.

When to be careful with the adductors

Groin strains are common in sprinting and kicking sports, and early return to heavy adductor work can aggravate them. See a physio or doctor if you have:

• sharp groin pain with squats, walking or running
• a recent pull or “pop” in the inner thigh
• deep hip pain or clicking that does not settle
• pain that wakes you at night or gets worse over weeks

Copenhagen planks are intense. Build the time over several weeks, and stop if you feel a sharp pull. Do not treat pain as a sign the exercise is “working.”

The bottom line

Adductors respond to being trained, and they get a lot of work in deep, full-range squats. Add a few sets on the adductor machine for extra volume and Copenhagen planks for groin strength, and be honest about what is known: the squat-depth data is solid for a small trial, the football data is good for injury and strength, and direct growth data for the machine is missing. Judge by your thigh measurements and your lifts over 8-12 weeks, not by hype. If your hamstrings also need attention, our piece on Nordic hamstring curls pairs well with this one.