en آسیب شناسی ورزشی و حرکات اصلاحی Sport injury and corrective exercises پژوهشي Research <div style="text-align: justify;"><strong>Purpose</strong>: Over-pronated foot (OPF) is a common abnormality of the foot. Sand can change lower limb muscle activities. Therefore, the aim of this study was to evaluate the effect of a sand exercise program on knee muscle co-contraction in runners with OPF.<br> <strong>Methods</strong>: Thirty individuals (age range: 18&ndash;26 years) with OPF were randomly allocated to the equally sized control and experimental groups. The experimental group performed a sand running exercise protocol for eight weeks. Muscle activities were recorded using an electromyography system. Two variables, including directed co-contraction and general co-contraction, were calculated before and after training programs.&nbsp;<br> <strong>Results</strong>: In the experimental group, lower directed vastus lateralis/vastus medialis co-contraction, greater general knee co-contraction, and directed medial/lateral knee co-contraction during the mid-stance and push-off phases were found at the post-test compared to the pre-test (P<0.017). Irrespective of the time, greater directed medial/lateral knee co-contraction during the push-off phase was observed in the experimental group (P=0.043).&nbsp;<br> <strong>Conclusion</strong>: Sand can be used as a suitable surface for training, as increased muscle co-activation is required to make postural adjustments during running.&nbsp;</div> Over-pronated foot, Co-contraction, Sand exercise, Running 215 224 http://ptj.uswr.ac.ir/browse.php?a_code=A-10-348-8&slc_lang=en&sid=1 Amir Fatollahi amiraf14618@gmail.com 0000-0002-0192-4358 No Department of Sport Biomechanics, Faculty of Educational Sciences and Psychology, University of Mohaghegh Ardabili, Ardabil, Iran. Amir Ali Jafarnezhadgero amiralijafarnezhad@gmail.com 0000-0002-2739-4340 Yes Department of Sport Biomechanics, Faculty of Educational Sciences and Psychology, University of Mohaghegh Ardabili, Ardabil, Iran. Hamed Sheikhalizade hamed.sh2102@gmail.com 0000-0002-5788-4447 No Department of Sport Biomechanics, Faculty of Educational Sciences and Psychology, University of Mohaghegh Ardabili, Ardabil, Iran.