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Effect of Modified Clamshell Exercise on Gluteus Medius, Quadratus Lumborum and Anterior Hip Flexor in Participants with Gluteus Medius Weakness
J Korean Soc Phys Med 2019;14(2):9-19
Published online May 31, 2019;
© 2019 Journal of The Korean Society of Physical Medicine.

Seom-Gyeul Jeong · Heon-Seock Cynn · Ji-Hyun Lee · Silah Choi · Daeun Kim

Department of Physical Therapy, Graduate School, Yonsei University
Received November 21, 2018; Revised January 9, 2019; Accepted January 31, 2019.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
PURPOSE: This study compared the effects of three different clamshell exercises (CLAM) on the gluteus medius (GMED), quadratus lumborum (QL), anterior hip flexor (AHF), gluteus medius/quadratus lumborum ratio, and gluteus medius/anterior hip flexor ratio by studying the activities of participants with GMED weakness.
METHODS: Eleven subjects with weak GMED participated in this study. Subjects performed CLAM under three different conditions (standard, and modified 1 and 2). Surface electromyography was then used to measure the muscle activity and one-way repeated-measures analysis of variance was used to assess the statistical significance of the measured variables.
RESULTS: GMED and the QL muscle activities did not differ significantly between the standard CLAM and the modified CLAM with the 2 different foot positions (F=4.74, P=.02; F=4.57, P=.02, respectively). AHF activity was significantly different in the two different foot positions when compared to the standard CLAM (F=11.17, P=.00). However, there was no significant difference between the AHF activities for the two different foot positions (P=.09). Finally, GMED/QL and GMED/AHF ratios were not significantly different between the three different CLAM exercises (F= .63, P=.55; F=.82, P=.45, respectively).
CONCLUSION: Modified CLAM can be recommended as a good method to minimize AHF activity while maintaining GMED activity in subjects with weak GMED.
Keywords : Anterior hip flexor, Clamshell exercise, Electromyography

May 2019, 14 (2)
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