Tehran University Medical Journal

Normal 0 false false false EN-US X-NONE AR-SA MicrosoftInternetExplorer4 Background: Muscle weakness and fatigue are two factors that cause muscle injuries. The roll of motor control is important in regulation and reduction of this effect. Repetition of motion after muscle fatigue is due to the significant role of motor control system. The aim of this study was to evaluate the quality of roll control of central nervous system following fatigue in order to answer primary questions in therapeutic exercises.
Methods: Twenty voluntary healthy subjects participated in this study. Dominant abductor policis brevis after surface electromyography (SEMG) of maximal voluntary contraction (MVC) fatigued by maximum three minutes isometric contraction in specific hand splint monitored by dynamometer until reduction of activities to 50% MVC. Before and immediately after fatigue test, 5 dynamic full range of motion in abduction direction performed without resistance and muscle activities recorded by SEMG. Three middle muscle activities selected for comparison of Symmetrical Index (SI) as specificity of motor control assessment. Fatigue indicators were percentage of reduction of MVC and median and mean frequency of power spectrum of MVC before and after fatigue test.
Results: Significant reduction of MVC (46.77%), median (13.03%) and mean (12.20%) frequency were showed (p=0.001), whereas significant increase of SI (10.76%) appeared (p=0.000), following fatigue test.
Conclusion: Fatigue reduces muscle contraction velocity, therefore median and mean frequency decrease. Also after muscle fatigue reduces of muscle proprioception sense appears, that can cause slow dynamic joint motion. Upper central control systems try to correct this situation by involving new motor units and changes of muscle timing. Synchronization of primary and new motor units plays an important role in increase of SI.