Purpose: Postural control preserves organs and body parts in a proper biomechanical stance which exists in two forms: static and dynamic. Fatigue is one of the factors that affects postural control. This study aimed to compare the electromyography (EMG) activity of the lower extremity muscles before and after fatigue.
Methods: This study was descriptive correlational and based on the research type a field study. Study sample comprised 20 male students majored in physical education; they were purposefully selected by non-accidental all-accounted method. Surface EMG activities of lower extremity muscles before and after fatigue were evaluated by electromyogram. To create fatigue in lower extremity muscles, we used fatigue protocol by the Biodex system. Data analysis was carried out by using SPSS 21. The paired t test was used for statistical analysis with a significance level of P<0.05. 
Results: The paired t test results indicated that the activity level of the rectus femoris, hamstrings, tibialis anterior, and gastrocnemius muscles significantly changed before and after fatigue. The study results also supported that lower extremity muscle fatigue had a negative effect on the activity of the muscles around the knee joint. Furthermore, there was a significant relationship between the postural control and the activity level of rectus femoris and tibialis anterior muscles on pretest. However, there were no significant relationships between postural control and activity level of lateral hamstrings and gastrocnemius muscles on pretest and posttest, nor the activity level of rectus femoris and tibialis anterior posttest. 
Conclusion: Muscle fatigue increases joints vulnerability. These results can be used in designing athlete’s rehabilitation programs and trainings to prevent injuries or changes in biomechanical parameters of walking.