Hip Adductor Muscle Forces During Strength Training and Rehabilitation Exercises

BACKGROUND: The hip adductors are crucial for athletic performance and injury prevention; however, the most effective exercises for targeting specific muscles are unknown. This study aimed to rank strength training and rehabilitation exercises based on individual hip adductor muscle forces and describe associated muscle fiber lengths, velocities, and activation ranges. METHODS: Fifteen injury-free participants performed 8 common hip adductor exercises: squat, deadlift, sumo deadlift, step up, lateral slide, lying leg lift, and Copenhagen adduction exercise (short- and long-lever). Three-dimensional kinematics, ground reaction forces, and surface electromyography (EMG) were used as inputs to an EMG-assisted neuromusculoskeletal model to estimate adductor brevis, longus, and magnus (pubofemoral/ischiocondylar), and gracilis muscle forces. Exercises were grouped into three 'tiers' using k-means clustering based on peak normalized muscle forces. Fiber lengths, fiber velocities, and activations were also compared between exercises. RESULTS: Copenhagen long-lever was Tier 1 for all adductor muscles. Copenhagen short-lever was Tier 1 for adductor brevis and longus. Deadlift and sumo deadlift were Tier 1 for adductor magnus ischiocondylar and gracilis, while step up and squat were Tier 1 for adductor magnus (ischiocondylar). Lateral slide was Tier 2 for all muscles. Lying leg lift was Tier 2 for adductor brevis and longus and Tier 3 for adductor magnus and gracilis. Squat was Tier 2 for adductor longus, adductor magnus (pubofemoral), and gracilis. Step up was Tier 2 for gracilis and Tier 3 for adductor brevis, longus, and magnus (pubofemoral). CONCLUSIONS: Copenhagen adduction exercise produced the highest forces across most hip adductor muscles. High adductor magnus (ischiocondylar) forces were generated during hip extension-oriented exercises. These rankings may guide exercise selection and load progression/regression for performance, injury prevention, and rehabilitation.