Behaviour of a surface EMG based measure for motor control: Motor unit action potential rate in relation to force and muscle fatigue

• Published in: Journal of electromyography and kinesiology Vol. 18; no. 5; pp. 780 - 788
• Main Authors: Kallenberg, L.A.C, Hermens, H.J
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.10.2008
• Subjects: Action Potentials - physiology; Algorithms; Computer Simulation; Data Interpretation, Statistical; Electromyography - methods; Feedback - physiology; Female; Healthy subjects; Humans; Male; Models, Biological; Models, Statistical; Motor control; Motor Neurons - physiology; Motor unit action potentials; Multi-channel surface EMG; Muscle Contraction - physiology; Muscle Fatigue - physiology; Muscle, Skeletal - physiology; Physical Medicine and Rehabilitation; Statistics as Topic; Stress, Mechanical; Young Adult; Motor unit action potentials; Healthy subjects; Multi-channel surface EMG; Motor control
• ISSN: 1050-6411; 1873-5711
• DOI: 10.1016/j.jelekin.2007.02.011

Abstract Surface electromyography parameters such as root-mean-square value (RMS) and median power frequency (FMED) are commonly used to assess the input of the central nervous system (CNS) to a muscle. However, RMS and FMED are influenced not only by CNS input, but also by peripheral muscle properties. The number of motor unit action potentials (MUAPs) per second, or MUAP Rate (MR), being the sum of the firing rates of the active motor units, would reflect CNS input solely. This study explored MR behaviour in relation to force and during a fatiguing contraction in comparison to RMS and FMED. In the first experiment ( n = 10) a step contraction of shoulder elevation force (20–100 N) was performed while multi-channel array EMG was recorded from the upper trapezius muscle. The sensitivity of MR for changes in force (1.8%/N) was almost twice as high as that of RMS (0.97%/N), indicating that MR may be more suitable for monitoring muscle force. The second experiment ( n = 6) consisted of a 15-min isometric contraction of the biceps brachii. MR increased considerably less than RMS (0.9% vs. 4.1%), suggesting that MR selectively reflects central motor control whereas RMS also reflects peripheral changes. These results support that, at relatively low force levels, MR is a suitable parameter for non-invasive assessment of the input of the CNS to the muscle.