Experimental investigation of human wrist muscle coordination strategy
Date of Issue2016-05-25
School of Mechanical and Aerospace Engineering
Robotics Research Centre
It is a well-known fact that human body has more degrees of freedom (DoF) than are strictly necessary to perform a movement or exert an external force. There are various patterns of muscle coordination to produce a desired movement or force (Bernstein, 1967). It is often described as Muscle redundancy problem. This paper explores how Central Nervous System (CNS) controls the redundant muscles by experimental approach. More specifically, Force Covariance Map (FCM) as introduced by Kutch et al (2008) is used to investigate muscle activation from endpoint force fluctuation. Surface EMG data are recorded from five dedicated wrist muscles to serve as a complementary method to understand muscle activation pattern, as well as to estimate muscle activity range and preferred directions. In addition, Donders surface is drawn for each subject from the wrist orientation matrix recorded in the pointing task, and the wrist stiffness ellipse is generated to find any possible relationship with the FCM. There are mainly three findings in this research. Firstly, it is verified that FCM method can be used to investigate muscle coordination in human wrist. Secondly, during isometric task related to the wrist joint, prime movers are identified in some task directions. It suggests that the CNS adopts the flexible strategy to coordinate the wrist muscle according to the task direction and magnitude. Thirdly, the higher wrist stiffness indicates more muscle co-contraction, thus a small target-directed covariance is expected in FCM in that direction. This is observed in two of the subjects, but not the other three subjects. Therefore, it cannot be concluded whether the wrist stiffness is related to FCM for now. It is recommended that the same experiment can be done with more subjects, to further verify the findings. Furthermore, the mechanical setup of the experiment still has room for improvements.
Final Year Project (FYP)
Nanyang Technological University