fa آسیب شناسی ورزشی و حرکات اصلاحی Sport injury and corrective exercises پژوهشي Research <div style="text-align: left">Introduction: The aim of the current study was to measure ground reaction force and center of pressure (COP) during lower extremity perturbation in single leg standing whit knee flexion and extension in healthy subjects, in addition to revealing reliability of the device used for the related perturbation for using another studies, reliability is one of the characteristic of measuring instrument , this indicates that measuring instrument to what extent in the same conditions gives the same results. Materials and method: perturbation device was built firstly, rotational perturbation (trunk and femur rotation on weigh bearing tibia ) were applied to the dominant leg of 13 healthy subjects during single leg standing . Four models of rotational perturbation (external and internal tibial rotation with knee flexion and extension) were applied to the lower extremities to collect ground reaction force and centre of pressure in these subjects. Subjects attached to lower extremity perturbation device and standing whit single leg on force plate. Subjects were then asked to repeat the tests procedure after a week&rsquo;s interval. Results: The intra class correlation coefficient and Cronbanch&#39;s Alpha values during within and between sessions tests for four models of rotational distributions showed the relatively high reliability of these measurements during single leg standing , the intra class correlation coefficient exceeded 0.7 in all dominants. Conclusion: The relatively high reliability of ground reaction force and centre of pressure measurements during four different perturbations of external and internal tibial rotation with knee flexion and extension in healthy subjects suggests that these measurements can be used during single leg standing in future studies.</div> Lower Extremity Perturbation Device, lower extremity rotational perturbations, ground reaction force, single leg standing 29 34 http://ptj.uswr.ac.ir/browse.php?a_code=A-10-143-1&slc_lang=fa&sid=1 leila najafi لیلا نجفی najafi_pt@yahoo.com No isfahan university of medicah science علوم پزشکی اصفهان javid mostamand جاوید مستمند mostamand@rehab.mui.ac.ir Yes isfahan university of medical science علوم پزشکی اصفهان ali amiri علی امیری : amiri.alipt10@yahoo.com No iran university of medical science علوم پزشکی ایران behzad mahaki بهزاد مهکی behzad.mahaki@gmail.com No isfahan university of medical science علوم پزشکی اصفهان