Synergetic Control during Generation of a Maximal Isometric Effort by the Human Arm

This study is a continuation of the previous works on a theoretical description of the mechanism of motor control by the CNS under conditions of the performance of simple motor tasks by humans. We describe the process of development of maximal different-direction static efforts within the horizontal plane by the human arm, where the hand, shoulder joint, elbow joint, and the effort vector are within the same horizontal plane. The upper limb has been modelled by a musculoskeletal system comprising of the forearm and shoulder links, elbow and shoulder joints, and of eight muscles of the arm and brachial grid generating the corresponding forces. The problem has been reduced to that of linear programming and is resolved using the simplex method. The results of modelling demonstrated the existence of a complex system of optimization synergies, which changed significantly when the direction of the maximal effort vector was changed. This system of synergies is more complex in the case of generating the maximum effort with two arms connected at the palms. Despite the fact that the modelling results obtained looked rather unexpected and extraordinary from the aspect of a real neurophysiological research, they, nevertheless, can initiate some new ideas for experimental work.