Grant: Discovery Grants Program - Individual

People use muscular co-contraction when interacting with unstable environments. Why? It is thought that co-contraction prepares the body to instantly counter unexpected disturbances by increasing muscle stiffness, like an elastic resisting stretch. If this were true we would see instant differences in motion following a disturbance when co-contracting. However, my recent work only shows differences after 50ms when the neural system can contribute. This highlights that there is poor mechanistic understanding of how muscular co-contraction aids motor performance. The objective of this proposal is to understand how muscle co-contraction impacts neural and mechanical features of the motor system to improve performance. Project 1: Impact of limb properties and co-contraction on motor corrections This project will demonstrate that contributions of co-contraction to improving motor performance and includes neural control. To do this we will compare limb control following a mechanical perturbation applied to the elbow in 1) relaxed vs. co-contracted conditions, 2) countering unidirectional background loads vs. co-contracted conditions, and 3) when relaxed but simulating co-contraction by increasing elbow stiffness/viscosity using a Kinarm Exoskeleton Robot. Project 2: Link between co-contraction and spinal feedback We hypothesize that spinal feedback responses are augmented when co-contracting, improving limb control. We will compare spinal feedback responses following perturbations to the elbow across co-contracted, relaxed and opposing background load conditions. Additionally, we will quantify how this augmented spinal response at high levels of co-contraction may lead to detrimental performance. Project 3: Tasks that naturally elicit co-contraction To determine the robustness of co-contraction improving limb control we will quantify its performance benefits when it is naturally evoked, opposed to when participants voluntarily co-contract (as in Projects 1&2). We will develop tasks to naturally evoke co-contraction, and once deemed reliable we will apply mechanical disturbances and measure reactive responses. Additionally, we will investigate performance benefits of co-contraction in non-mechanical scenarios requiring rapid motor responses. Project 4: Generalizing co-contraction benefits across the body Finally, we will investigate the benefits of co-contraction when disturbances are applied to the hands and feet (disturbances only applied to elbow joint in Projects 1&2). This will better replicate the real-world where co-contraction is used when working with tools or walking on slippery surfaces. This work will provide a mechanistic understanding of how co-contraction improves motor performance, involving not only changes in muscle properties but also in altering neural control. These findings will inform application-based research and design for exposures to unstable environments, or to assess a range of neurological impairments.