The Changes of median frequency and power of neck extensor muscles following dynamic fatigue in healthy men

Neck muscles contract dynamically in the majority of daily activities. Athletes, agricultures and industrial labors are predisposed to muscular fatigue. The aim of the present study was to compare the effect of dynamic fatigue on power and frequency domains of EMG spectrum. In this study 20 healthy young men contracted neck muscles dynamically, until muscular fatigue occurs. Surface electromyography was recorded of levator scapula, neck paraspinals and upper trapezius, as neck extensors. The effects of dynamic contraction on frequency (Median Frequency) and Power domains(RMS) were compared before and after fatigue. The results of the present study indicated that MedF decreases following dynamic fatigue (P<0.05). After dynamic fatigue, RMS of levator scapula and upper trapezius increased significantly (P<0.05). Regarding to significant decrease of RMS and increase of MedF, paraspinals encountered with force reduction. Changes of MedF and RMS indicated that a continuous dynamic contraction tends to exhaust levator scapula and upper trapezius but decreases paraspinals force.