Background: Muscle fatigue has been known to influence brain activity, but very little is known about how cortical centers respond to muscle fatigue. Objective: This study was conducted to investigate the effects of muscle contraction and fatigue induced by two different percents of maximal voluntary contraction (MVC) on Electroencephalography (EEG) signals. Material and Methods: In this quasi-experimental study, EEG signals were recorded from twenty-one healthy human subjects during three phases (rest, pre fatigue and post fatigue) contraction of Adductor pollicis muscle (APM) at 30% and 70% MVC. The mean powers of EEG bands (alpha, beta and gamma) were computed offline in the frequency domain. Results: None of the three phases with each percent of MVC revealed significant differences for all bands (p>0. 05). Comparison of two hemispheres showed that right hemisphere gamma band activity was enhanced during pre-fatigue state at 30% MVC (p= 0. 042) and post-fatigue state at 70% MVC (p= 0. 028). Right hemisphere beta band activity also increased prominently at 70% MVC in post-fatigue condition (p = 0. 030). Conclusion: These results suggest muscle contraction and fatigue at 30% and 70% MVC have no significant effect on EEG activity, but the trends of beta and gamma band activities are almost similar in each percent of 30% and 70% MVC. Right brain hemisphere shows more activity than left hemisphere in beta and gamma rhythm after fatigue state at 70% MVC.

Background: Wearing back support is of great importance in helping muscles action in heavy works. Objective: To evaluate the effect of lumbosacral support on the degree of spinal muscle fatigue in normal persons. Methods: The study was conducted on 52 normal females as "case-control' group using Isostation B-200 unit. Three isometric contractions with maximum effort in flexion and extension was applied for each case in the first session without using back support. Then, fatigue exercise was performed with 50% of maximum muscle power in flexion and extension and the maximum isometric power was again measured. On the next day, the same procedure was performed using back support. Findings: Increase of the average of torque, power, maximum and average angular speed was significant while wearing back support (P<0.05). Also, the mean of maximum torque and maximum angular speed in last repetitions, with and without back support were significantly decreased in comparison with first repetitions (P<0.05). Conclusion: Since using lumbosacral back support will cause improvement in speed of repeated motions, less function and delayed fatigue of paravertebral muscles, the use of back support during working hours in heavy works is highly recommended.