Acute Effects of Copenhagen Adduction Exercise on the Stiffness and Soreness of the Hip Adductors: A Randomised Controlled Trial with Reliability Assessments

Groin injuries often happen in sports involving quick direction changes, kicking, and rapid movements, with the adductor longus frequently being affected. The Copenhagen Adduction Exercise (CAE) is commonly used to help prevent such injuries. This randomised controlled trial examined the immediate effects of a single CAE session on hip adductor stiffness and perceived muscle soreness in physically active adults, following the CONSORT 2025 guidelines. Twenty-six participants (16 females, 10 males) were randomly assigned to either a CAE group, performing three sets of ten repetitions, or a control group that did not exercise. Stiffness of the adductor longus and adductor magnus was measured with the MyotonPro device before and after the intervention, along with a 0-100-point soreness scale. Intra-rater test-retest reliability for stiffness measurements was high to excellent for both muscles (ICC ≥ 0.93). The CAE group showed a significantly greater increase in adductor longus stiffness (p=0.002) and soreness (p<0.001) compared to the control, while there was no significant difference for adductor magnus stiffness (p=0.162). Changes in adductor longus stiffness were moderately positively correlated with perceived soreness (R=0.543, R²=0.295, p=0.004), but no such relationship was observed for adductor magnus. These results indicate that CAE elicits a specific, short-term mechanical and perceptual response mainly in the adductor longus. Although these reactions likely reflect normal eccentric loading rather than injury, further long-term studies are needed to determine whether repeated CAE enhances adaptations
related to groin injury prevention.