Objectives To describe a novel method for measuring eccentric hip adductor (EHAD) strength during the Copenhagen adduction exercise (CAE) and investigate the test re-test reliability of this measure. Design Test re-test reliability study. Participants Twenty male athletes aged 24 ± 6 years participated in two data collection sessions 7 ± 2 days apart. Main outcome measures During each data collection session, participants performed three maximal effort repetitions of the CAE with their leg supported by an ankle strap hung from a fixed barbell. We attached a commercially available load cell in-series with the ankle strap to measure peak force in Newtons (N) during the eccentric lowering phase of the CAE. The intraclass correlation coefficient (ICC), standard error of measurement (SEM), SEM as a percentage of the mean (SEM%) and minimal detectable change at a 95% confidence interval (MDC95) were calculated for this measure of EHAD strength. Results Test re-test reliability was good for EHAD strength measured during the CAE on dominant (ICC = 0.84; SEM% = 3.6%; MDC95 = 33 N) and non-dominant (ICC = 0.87; SEM% = 3.3%; MDC95 = 29 N) legs. Conclusions This study provides proof-of-concept that EHAD strength can be measured during the CAE with good test re-test reliability.