Background: Many previous studies recommended the side-lying hip abduction (SHA) exercise for targeting the gluteus medius (Gmed) and gluteus maximus (Gmax) muscle activity while the decreasing tensor fasciae latae (TFL) activation. Mischoice of hip position and angle in SHA may increase the risk of lower extremity injuries and undesirable muscle activation. However, information is limited on the effect of composite hip flexion angles and hip rotation on the gluteal muscle activity during SHA.
Objects: This study aimed to compare muscle activity (Gmed, TFL, and Gmax) and activity ratios (Gmed/TFL, Gmax/TFL, and Gmed/Gmax) using surface electromyography (EMG) during SHA exercise at three different hip flexion angles either with or without internal rotation (IR) in subjects with Gmed weakness. We hypothesized that applying hip flexion and IR during SHA would increase gluteal muscle activity and decrease TFL activity.
Methods: Muscle activity and activity ratios in 20 volunteers with Gmed weakness during 6 different SHA were investigated with surface EMG. One-way repeated-measures analysis of variance was used to determine the statistical significance.
Results: Significant differences were found among the six different exercises for Gmed (F2,41=11.817, p<.001) and Gmax (F3,52=5.513, p=.003) muscle activity, and Gmed/TFL (F3,54=8.735, p<.001) and Gmax/TFL (F2,37=4.019, p=.028) activity ratios.
Conclusion: Applying hip flexion is an effective method for increasing gluteal activity, and it elicits great Gmed/TFL and Gmax/TFL activity ratios during SHA in subjects with Gmed weakness.

Introduction
 Methods
  Subjects
  Surface EMG recording and dataprocessing
  Three-dimensional (3D) motion analysissystem
  Procedures
  SHA with neutral hip and flexion0°(SHA-NF 0)
  SHA with neutral hip and flexion15°and 30°(SHA-NF 15 and 30)
  SHA with hip internal rotation andflexion 0°(SHA-IRF 0)
  SHA with hip internal rotation andflexion 15°and 30°(SHA-IRF 15 and 30)
  Statistical analysis
 Results
  Muscle activity of Gmed, TFL and Gmax
  Muscle activity ratios of Gmed/TFL,Gmax/TFL and Gmed/Gmax
 Discussion
 Conclusion
 References

• Hye-jin Park(Dept. of Physical Therapy, The Graduate School, Yonsei University)
• Sang-hyun Cho(Dept. of Physical Therapy, College of Health Science, Yonsei University, Dept. of Ergonomic Therapy, The Graduate School of Health and Environment, Yonsei University) Corresponding Author