Mechanisms altering skeletal muscle activation patterns during dynamic tasks

Because our trunk makes up 68% of our overall body mass, it is important to study how we control trunk posture and motion. We must be able to control trunk position to perform many activities of daily living such as walking, sitting, and lifting objects to high performance athletic skills. Trunk muscles also protect the spine from excessive motion by producing stabilizing forces. Numerous muscles and joints are involved so my research looks at how changes in joints, bones and muscles alter how this complex system works together to maintain spine stability and control trunk motion. The central nervous system controls how the muscles work together. When there are changes in joint structures or surrounding muscles (e.g. increased joint laxity, decreased muscle strength) then the nervous system can adapt to change how muscles work. Using surface electromyography (EMG)) from a large number of muscles I want to understand how the nervous system adapts to specific changes in joint structures that alter how the muscles work together. We have naturally occurring changes in the body to joints, bones and muscles with age, pathology, and differences between men and women. Studying these populations provides a natural experimental model to look at how changes in these structures are compensated for by the neural control system. I have shown how the muscles respond in some cases by increasing how hard they work. In other cases, however, I have shown that the muscles do not work together in a typical manner. I want to understand why this happens, and find out whether I can relate specific changes in the joint, bones and muscles to specific changes in how the muscles work. We will study a large group of people across a wide age range (20-80 years) while they perform standard movements. A number of measures will be taken that help determine which factors are most important to the changes in how the muscle work together to move and protect the spine. The second question is to determine whether we can link the specific patterns of how the muscles work with specific patterns of activity in the part of the brain that controls movement. We will combine activation measures from the trunk muscles (EMG) and from the brain (electroencephalography) to determine these links. Finally I want to understand what effect these changes in trunk muscle responses have on the forces that are applied to the joint. To do this we will advance present methods of estimating these forces by using age, sex and pathology-specific information. At present the information used in these models are from young healthy, primarily men which does not give us a good estimate across the life span. This will inform us of whether the muscle alterations have a positive or negative impact on the joint. The long-term goal is to advance knowledge of the factors important to control trunk function and develop tools that will impact research and technology in broad areas related to human movement performance (e.g. work place, activities of daily living, high performance athletics, clinical settings and robotics). For example, given our aging workforce, being able to understand limits and potential changes to work space design would be helpful as many tasks are performed in seated and standing positions. As well popular magazines across a wide range of areas talk about "core" stability but there is really little scientific evidence to back many claims and the results of this study will provide information which may lead to training both physical and mental aspects of control. Finally the ability to control trunk position is necessary to perform many tasks on unstable surfaces such as the military and offshore workers.