A neuromechanical approach to define muscle recruitment strategies and control of the upper limb

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To complete most activities of daily living we must coordinate limb movements through the control of muscles in the upper extremity. As humans, we continuously interact with tools and objects in our environment and we are often presented with situations where objects and tools apply variable forces and torques to the hand. This further challenges our ability to provide control. Muscle actions must counter an external disturbance and these actions are governed by the central nervous system and depend on the external conditions, task demands and limb posture. Biomechanical characteristics partially dictate roles for each muscle, but mechanical output is ultimately a consequence of signals sent by the central nervous system to the muscle. These neuromechanical aspects need to be considered to fully understand the links between motor commands, neural activity and limb mechanics. My research implements an approach to the development of a paradigm that better understands how the central nervous system controls hand and arm motion during workplace related tasks. The workplace provides a unique environment to study these changes since both fine and gross motor skills are needed daily to perform upper extremity tasks. This work uses perturbation experiments and fatigue protocols to simulate workplace demands and then uses electrical stimulation techniques (including transcranial magnetic stimulation, nerve and muscle stimulation) and computer modelling to bridge the gap between neural and biomechanical factors. Focusing on the manipulation of individual muscle parameters (force, length, velocity and fatigue) this work evaluates recruitment strategies due to changes in muscle mechanics and muscle roles (co-activation vs. antagonists). Muscle recruitment and control strategies will be determined such that a framework for identifying co-contraction and synergist muscle actions are established. This work is novel and spans several disciplines to evolve our understanding of how the central nervous system drives muscles to perform actions. This work is important to industrial applications and will lead to improved human factors and engineering of both the workplace and of tool design.