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Background: Low back pain is closely associated with hip muscle dysfunction, particularly weakness of the gluteus medius, which plays a critical role in pelvic and spinal stability. The clamshell exercise is widely used in rehabilitation to strengthen the hip abductors; however, its effectiveness may be limited by compensatory activation of synergistic muscles. This study investigated the effects of ankle joint movement variations on hip muscle activity during the clamshell exercise. Methods: Twenty-four healthy adults with no orthopedic or neurological disorders in the past six months performed five exercise conditions: clamshell exercise (C), clamshell exercise with ankle inversion resistance (CIR), clamshell exercise with ankle eversion (CE), clamshell exercise with ankle eversion and eversion resistance (CEER), and clamshell exercise with ankle eversion and inversion resistance (CEIR). Surface electromyography was used to measure the activities of the gluteus medius (Gmed), tensor fascia latae (TFL), and gluteus maximus (Gmax), normalized to %MVIC. A one-way repeated-measures ANOVA with Bonferroni post-hoc tests was conducted to compare differences between conditions. Results: CEER elicited significantly greater Gmed activity compared with all other conditions (p<.05) and demonstrated the highest Gmed/TFL activation ratio, indicating reduced compensatory TFL involvement. Gmax activity was also significantly greater in CEER than in C (p<.05). CIR and CEIR produced significantly higher TFL activity compared with other conditions (p<.05). Conclusion: The clamshell exercise incorporating ankle eversion with eversion resistance effectively increased Gmed and Gmax activation while minimizing TFL overactivation. This approach may enhance hip muscle recruitment patterns and serve as a targeted rehabilitation strategy for individuals with low back pain or lower extremity dysfunction.