Tehran University of Medical Sciences Journal of Modern Rehabilitation 2538-385X 10 2 2017 01 22 61 66 Zeinab Mohammadjannataj MSc Student, Department of Physical Therapy, School of Medical Sciences, Tarbiat Modares University, Tehran, Iran Sedigheh Kahrizi Assistant Professor, Department of Physical Therapy, School of Medical Sciences, Tarbiat Modares University, Tehran, Iran Noshin Bayat Associate Professor, Department of Rheumatology, School of Medical Sciences, Baqiyatallah Hospital, Baqiyatallah University of Medical Sciences, Tehran, Iran 2017 01 21 Introduction: According to the importance of the back extensor muscle strength in postmenopausal women, this study aimed to determine the relationship between strength and changes in the thickness of back extensor muscles during isometric contraction in healthy and osteoporotic postmenopausal women. Material and Methods: 42 volunteer postmenopausal women according to their Bone Mineral Density divided into two groups “healthy” and “osteoporosis.” Strength and thickness of the muscles were measured, respectively, using a handheld dynamometer and ultrasonography. The interclass correlation was used to evaluate the relative reliability dynamometer and ultrasonography. In addition, the Pearson’s correlation coefficient was used to analyze the relationship between the strength and thickness. Results: The results indicated a high reproducibility dynamometer test and ultrasonography. There was a good significant positive correlation between strength and the thickness change of the muscles during isometric contractions in the healthy group (P < 0.050), but in the osteoporosis group, there was no significant relationship between these two variables. Conclusion: In postmenopausal women with osteoporosis, due to the low quality of muscles (muscular component of strength), changes of the muscle thickness is not in line with muscle strength during isometric contraction, so it is necessary special back muscle training for these subjects besides of other treat intervention from the point of rehabilitation https://jmr.tums.ac.ir/index.php/jmr/article/view/27 https://jmr.tums.ac.ir/index.php/jmr/article/download/27/24