Study On Spatial Character Of Extensor Digitorum Muscle During Sustained Contraction

The hand is one of the most flexible locomotive organs. To investigate the control of neuromuscular system on fingers concerted action and force output is of great importance to such aspects as clinical diagnosis of the neuromuscular disorder in the hands, functional rehabilitation, and studies on prosthesis and so on. While the complexity of hands’ anatomical structure and physiological function makes it so difficult to understand the control strategies of neuromuscular system. As the force output of fingers depends on the forearm multi-tend muscles, detection the surface electromyography(s EMG) of the forearm multi-tend muscles, and then analyzing the relationship between s EMG and the finger force is one of the effective methods to evaluate the control strategies on finger activities. With the development of detection technology of s EMG, multi-channel surface electromyography obtained by 2-D electrode array could provide us the spatial information of muscle activities, making for a more accurate estimation on activation and functional role of muscles, providing a more efficient means of investigating the control strategies of neuromuscular system. Therefore, this paper used 2-D electrode array to collect multichannel s EMG form extensor digitorum muscle(ED), one of the forearm multi-tend muscles, during its sustained contraction, extracted the spatial information of muscle activation, analyzed the relationship between these spatial information and finger movements, and then investigated the control strategies of neuromuscular system on fingers concerted action and force output.To extract the spatial information carried by multichannel s EMG, being visually displayed is always necessary for these multichannel signals. This paper designed a system in Labwindows/CVI virtual instrument environment to collect, display and save the multichannel s EMG, as well as achieve topographic visualization of forearm muscles’ electrical activity under different finger tasks, as a part of data processing module of this system. This program can meet the needs of our laboratory about multichannel s EMG. And the topographic maps drawn by this program can be used to display the spatial information of muscle activity for its clear expression on the differences of muscle activity intension.Then we used 2-D electrode array and force signal detection device, both designed by our laboratory, to collect multichannel s EMG form extensor digitorum muscle(ED) for the purpose of preliminarily investigating the control mechanism on fingers concerted action. When collecting signals, the experimental tasks consisted of three force levels(15%、30%、45%MVC) of separate fingers(the index and the middle), lasting for 90 s. RMS, the time-domain eigenvalue, was then calculated for each channel and next topographically displayed. By analyzing the relationship between the information extracted form topographic maps and finger tasks, following results was obtained:(1) RMStotal showed a linear dependence on force levels, means that the activity intension of ED is related to force levels;(2) The activity areas and intension of ED were significantly different between fingers when at the same force levels, the activity area of the index finger locating near radialis while that of the middle finger in proximal, and the activity intension of the middle finger larger than that of the index finger;(3) The trends of RMStotal of the index finger increased over time under all contractions. All in all, the activity areas and intension of ED were influenced by finger’s active patterns, and its spatial distribution changed unevenly with force level and duration time.MF eigenvalue was also calculated for the local information as the RMStotal was for the entire muscle. The amounts and distribution of these channels with MF significantly changed was recorded for muscle recruitment analysis. The results are as follows:(1) the amounts of those channels affected by the force levels and duration;(2) The distribution of these channels affected by the finger’s active patterns and force levels, but not by the duration;(3) the growth rate of RMStotal of those channels was significant larger than that of entire muscle. Those results showed that recruitment of ED was changed with force levels and duration, and its spatial distribution was influenced by the finger’s active patterns and force levels.