Tehran University of Medical Sciences Journal of Modern Rehabilitation 2538-385X 12 3 2019 04 20 195 200 Maryam Azizi Department of Physiotherapy, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran. Azadeh Shadmehr Department of Physiotherapy, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran. Kazem Malmir Department of Physiotherapy, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran. Nastaran Ghotbi Department of Physiotherapy, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran. Zahra Khazaei Pour Brain and Spinal Cord Injury Research Center, Tehran University of Medical Sciences, Tehran, Iran. 2019 04 20 Introduction: Flexibility is considered as one of the most significant components of rehabilitation protocols including two definitions: static flexibility measured by the Range of Motion, and dynamic flexibility measured by stiffness. Generally, a normal flexibility is necessary for an appropriate posture and flawless activity in daily life. With regard to various methods that contribute to increasing flexibility of hamstring muscles, the current study aimed at investigating immediate effects of Muscle Energy Technique (MET) on hamstring flexibility and stiffness in healthy young females Materials and Methods: Ten healthy young females with the mean age of 22.5±2.67 years old participated in the study. Flexibility was measured via active knee extension and modified sit-and-reach test, and stiffness was measured based on the ratio of torque to angular changes via Biodex System 3 before and after MET interventions by post-isometric relaxation method. Results: The amounts of active knee extension and modified sit-and-reach tests significantly increased after MET intervention; the amounts of active knee extension and modified sit-and-reach increased significantly (P<0.001). Moreover, the estimated hamstring stiffness decreased significantly in comparison with its values before treatment (P<0.001) Conclusion: The results of this study indicated that MET may improve hamstring flexibility as well as its stiffness. https://jmr.tums.ac.ir/index.php/jmr/article/view/184 https://jmr.tums.ac.ir/index.php/jmr/article/download/184/116