The purpose of this study is to find out the activity of gluteus medius muscle by the changes of load given to the upper limbs in single support phase. This study was twenty healthy men from A College. The left gluteus medius muscle was measured using SEMG(surface Electromyogram). Only the left foot was supported, and for the right foot, the right upper limbs were abducted while hip joint and the knee joint were bent at a 90° angle. The study was made by giving weight using dumbbells, depending on the RM of the subject(0RM, 1RM, 3RM, 5RM, 7RM). Gluteus medius muscle showed a large activity for those given weight to the upper limbs(1RM, 3RM, 5RM, 7RM) than that without weight(0RM). There was a significant difference in the activity of gluteus medius muscle between each RM. Gluteus medius muscle is high active when weight is given to the upper limbs in single support phase.