The Preliminary Study Of The Impact Of Finger Activity On The Motor Unit Recruitment Mode In The Forearm Multi-tendinous Muscle

The hand is one of the most flexible moving organs. The control of neuromuscular system on fingers concerted action and force is the important foundation of hand dexterous activities, and the control is realized by the control of downstream nerve impulses on the recruitment and firing of motor units in corresponding muscle. The recruitment and firing of motor units is specifically expressed as electromyography which could be detected. The use of electromyography to evaluate the control mechanism of the neuromuscular system on finger activities has become an important technical mean. As a non-invasive detection method, sEMG signal contains the recruitment information of motor units. The firing characteristics motor unit action potential (MUAP) extracted from sEMG signal could establish the mapping of the neuromuscular system and fingers activities effectively and directly, which have become a research focus in study the control mechanism of fingers activities. The outputs of fingers force depend on forearm multi-tendon muscles. Therefore, the paper extracted the recruitment mode of motor units in forearm multi-tendon muscle under different finger activities and analyzed the impact of finger activities on the recruitment mode, in order to explore the neural regulation mechanism of finger activities.First of all, the paper designs the force signal detection device to collect fingers force signal with functions of signal sampling, analog-digital conversion and storage. Finger force signal is converted to a voltage signal by JLBS-Π tension and compression sensor. The amplitude of the voltage signal is0-20mV, and the frequency is0-30Hz. Then the voltage signal is collected by the USB6008data acquisition card after transformed by amplifier, low pass filter and the circuit voltage uplift. Finally, the LabVIEW finger force detection software realizes the function of real-time display and storage.When collecting the finger force signal, sEMG signal of flex digitorum superficialis (FDS) was acquired by array electrode designed by our laboratory. The paper explored the recruitment mode of motor unit in FDS, under different finger patterns. Firstly,6-channel sEMG-signals were recorded on FDS used a6X2(row X column) electrode-array during the index finger compression task (6,8,10and12N). The time-domain eigenvalue of RMS was calculated for each channel, and then the correlation between RMS and finger force level and the correlation between RMS and FDS anatomy position were analyzed. Considering the individual differences between participants and perfect experimental conditions, the experimental program was modified to index finger and middle finger compression task (20%,40%,60%MVC) and1×7(row X column) electrode-array.Because time-domain eigenvalue RMS would be affected by the peripheral muscle characteristics, the number of MUAP, firing mode of MUAP and inter-pulse interval of MUAP, depending on the central nervous muscle control system, were then selected to describe the recruitment mode of motor unit. FastICA algorithm was used to decompose sEMG-signal, and combined with manual identification method to isolate single MUAP waveforms. The number of MUAP, the firing patterns of MUAP and inter-pulse intervals of MUAP were statistical analyzed, and the correlations between them and patterns of finger activity were extracted.The main achievement of experiments could be presented as follows:(1) The RMS of sEMG signal of all channels, scilicet muscle activation intensity, increased with the increase of force level;(2) The correlation coefficients of finger force and RMS in the different location of FDS were different;(3) The firing number of MUAP on FDS increased with the increase of force level;(4)The firing mode of the four types of MUAP in index finger activity pattern were different from in middle finger activity pattern;(5) At the same force level,the contribution rates to finger force of the four types MUAP were different;(6) The inter-pulse interval of four types MUAP met the theoretical value;(7) The firing rate and stability among four types MUAP were different, which met the theory that the firing rate of the low-threshold motor unit is slow and firing stably, and the firing rate of high-threshold motor unit is fast but not regularly;(8) Under index finger and middle finger activity patterns, the correlations between firing mode and finger force were consistent with the correlations between the approximate entropy of inter-pulse interval sequence and finger force, which showed that the faster the motor unit firing rate, the worse the stability.These preliminary experimental results showed that the selectivity of recruitment of motor unit in FDS was affected by internal factors and external factors. The external factors included finger force level, electrode position and finger activity patterns, and the internal factors included recruitment threshold of motor unit and neuromuscular unit partition. The combined effects of internal and external factors completed the regulation of fingers activities.