Objectives: There are two sub systems of paraspinal muscles, the global-mobilizing system and the local stabilizing system. The multifidus muscles are assigned to the local system and stabilize the joints. In contrast, the longissimus muscles are assigned to the global system and force exertion. This study aimed to investigate the median frequency changes in mobilizing and stabilizing muscles following fatigue. Method: A cross sectional study was designed. sEMG measurements were recorded from twenty participants following a fatigue protocol in B200 dynamometer. Participants performed dynamic trunk flexion-extension against a moderate resistance while standing in a static dynamometer until they could no longer performs the task because of fatigue. Results: Statistical analyses showed significant differences between median frequencies pre and post fatigue (P<0.05). Median frequency of the right and left multifudus muscles reduced from "99.12 and 93.2" to "86.55 and 85.85" respectively. Also Median frequency of the right and left longissimus reduced from "76.54 and 76.82" to "66.43 and 68.55" respectively. Conclusion: Median frequency shift toward low values following fatigue in global and local paraspinal muscles was seen. However, median frequency values for the local stabilizer muscle were higher than median frequency values for the global muscles.