Kinetic Analysis Of Sensorimotor Control During Precision Grip

The dexterous movements of hands are essential for human life and work,and the thumb opposition with index finger provides a physiological foundation for all kinds of delicate and complex performances.The precision grip has many sensorimotor mechanisms underlying the motor control,which playing an important role in basic research and clinical diagnosis.Many factors can influence the precision grip,such as subjects,manipulated object and tasks.This study had carried out a series of experiments to explore the effects of these factors on kinetics during precision grip in healthy adults.This paper completed following main works:(1)Effects of exercise-induced local muscle fatigue on precise grip.Local muscle fatigue resulting from long-duration movement will lead to the weakness of human function,and the coordination and flexibility of motion will be decreased.Usually,the mean value and fluctuation of force output,the magnitude and the power spectrum of surface electromyogram signal(sEMG)were used to evaluate the influences of fatigue.In our study,the exercise-induced fatigue task and precision grip performed by both hands were designed.Three parameters including normal force,the center of pressure and force vectors of the two digits during precision grip before and after the fatigue task were calculated to assess the effects.The statistical results had shown there was no significant effects on force output,and the center of pressure only affected by the right hand fatigue,only the force vector was effective to measure the local fatigue,which showing that the force vector had a tendency to deviate further from the direction of normal force.Meanwhile,there was no evidence of contralateral transfer of exercise-induced local muscle fatigue(peripheral fatigue).(2)Effects of unknown external torque on precise grip.A well precision grip performance not only requires real-time feedback modulation,but also forward prediction based on experience and motion memory.When manipulating the familiar objects,accurate and fast precision grasp can be completed according to experience,while grasping unfamiliar object or vision illusion,the prediction errors would occur.It's necessary to learn and correct the errors via repeated trials to make the movement more effective.In this research,the object with unknown center of gravity bias was used,the subjects were asked to keep the object balance and stable with minimum tilt.The results indicated with trials(2-3 times)the maximum roll angle,the compensatory torque and the time interval could reach the ideal state and tend to be stable,which suggested that the forward prediction and the backward feedback making the precision grip perfect.Meanwhile,the linear correlation analysis was carried out on the difference of vertical shear force(dLF)and the vertical distance of digit center of pressure of the two digits(dCOP),and the normal force(GF)from the last three trials.The significant negative correlation between dLF and dCOP,indicating the integration of kinematics and kinetics of sensorimotor control during precision grip.(3)Effects of removing visual feedback on precise grip.The environment,manipulated object and human are the basic factors for one task,and the connection among them is mainly transmitted through visual feedback.During precision grip,the visual feedback provides the information of the grasped object to generate the motion plan and prediction before contraction,and regulates the online performance during movement combining with tactile sensory and proprioception.The study aimed to examine the kinetic parameters in the condition of removing the visual information of target object,hand and forearm,including temporal parameters(reach,preload and load phase),force parameters(maximum load force,maximum grip force and safety margin)and object position(three-direction coordinates and coefficient of variation).Results showed visual feedback mainly influenced the initial of precision grip,especially prolonged the reach and preload duration and increased the maximum load force during loading.During the stable phase,each subject kept their own distinct safety margin,no significant effects was found.The overall study indicated that visual feedback mainly affected the subjects' confidence and speed during precision grip,as well as motion plan.