Effects of Copenhagen adduction exercise on muscle architecture and adductor flexibility

Key points

1. 018 weeks of CAE increased adductor longus muscle thickness by roughly 17-18% bilaterally (p < 0.001, d > 1.77)
2. 02Hip abduction range of motion improved by about 7% bilaterally after training (p < 0.05, d ~0.95)
3. 03Both muscle thickness and flexibility returned to pre-training values after 4 weeks of detraining
4. 04The control group showed no significant changes in either variable throughout the study
5. 05CAE was performed in isolation without other training, confirming the changes were due solely to this exercise

How it was conducted

Design

Randomised controlled trial with pre-training, post-training, and post-detraining measurements

Participants

45 healthy male recreational exercisers, mean age 26.1 +/- 2.8 years, no lower limb injury in the prior 12 months

Groups

Experimental group (n = 25): 8 weeks CAE training + 4 weeks detraining; Control group (n = 20): no intervention

Primary outcomes

Adductor longus muscle thickness via 2D ultrasound; hip abduction range of motion via goniometry

Training protocol

Progressive CAE sessions, 3 s eccentric and 3 s concentric tempo, at least 24 h between sessions, with standardised warm-up

Duration

13 weeks total (1 week baseline, 8 weeks training, 4 weeks detraining)

What they found

• Adductor longus muscle thickness increased significantly in the experimental group from M1 to M2: left leg +17.83% (t = -9.76, d = 1.77, p < 0.001), right leg +18.38% (t = -9.96, d = 1.82, p < 0.001)
• After detraining, muscle thickness decreased significantly back toward baseline: left leg -14.66% (t = 6.43, d = 1.32, p < 0.001), right leg -14.20% (t = 6.38, d = 1.30, p < 0.001)
• Hip abduction range of motion increased significantly after training: left leg +7.3 degrees (t = -4.41, d = 0.96, p < 0.05), right leg +7.15 degrees (t = -4.39, d = 0.94, p < 0.05)
• Hip abduction ROM decreased significantly after detraining: left leg (t = 4.02, d = 0.81, p < 0.05), right leg (t = 3.81, d = 0.72, p < 0.05)
• Control group showed no significant changes in muscle thickness or ROM at any time point (all p > 0.05)
• Test-retest reliability was high: muscle thickness ICC = 0.92-0.94; flexibility ICC = 0.95-0.97
• Compliance in the experimental group was 99%

Limitations

• Sample included only men, limiting generalisability to women and other populations
• Only adductor longus muscle thickness was measured; other adductors and architectural variables (e.g., fascicle length, pennation angle) were not assessed
• No direct measure of adductor strength was included, so the link between architectural changes and strength gains is inferred rather than confirmed
• Single-centre study with a relatively small sample size; results may not generalise across different sports or fitness levels

Why it matters

For patients

If you do Copenhagen adduction exercises for 8 weeks you can expect your inner thigh muscle to grow and your hip flexibility to improve, but you need to keep exercising to hold onto these gains.

For clinicians

CAE alone produces large-effect structural changes in the adductor longus and meaningful flexibility gains that reverse rapidly on detraining, supporting its use in active prevention and rehabilitation programmes with built-in maintenance dosing.

For readers

This is the first RCT to isolate CAE effects on adductor architecture and flexibility, confirming structural adaptation follows an eccentric stimulus pattern seen in other lower limb muscles, with full reversibility after 4 weeks of rest.