Mapping threshold specific motor unit adaptation to ageing with injectable EMG arrays

The global population is ageing rapidly due to advancements in healthcare. However, while people are living longer, many spend a greater portion of later life in poor health. One major factor contributing to this is a decline in neuromuscular function, where muscles become weaker and harder to control. This increases the risk of falls, social isolation, and reliance on healthcare services. Although we understand a great deal about how muscles change with age, we know far less about the nerves that control them. These motor nerves vary based on the tasks they perform. For example, nerves responsible for small, precise movements, like picking up a pen, may be less affected by ageing than those controlling powerful movements, like climbing stairs or recovering balance after tripping. Importantly, much of what we know about ageing nerves comes from studies focused on smaller, less affected tasks. This project aims to fill the gap in our understanding by studying how these changes impact the larger, more critical movements needed for daily life and independence. This gap in knowledge is largely due to methodological limitations. However, recent technological advancements have led to the development of new equipment capable of recording muscle and nerve activity across the full range of muscle forces, even during functional tasks like walking. These devices have been successfully tested in various animal models, and we are among the first to trial them in humans. The technology consists of a small, flexible film embedded with sensors that can be safely and securely injected into human muscles during activity. This allows us to measure how effectively motor nerves communicate with muscles, with the added advantage of recording from deeper muscle regions and during larger contractions—something that was previously impossible. The aim of this project is to use cutting-edge technology to advance our understanding of age-related adaptations in the human motor system, with a focus on exploring the full range of motor nerves involved in functional tasks. In healthy young and older males and females, we will record muscle and nerve activity across different muscle groups during various tasks. From this data, we will estimate the total number of motor nerves, assess their activation patterns, and evaluate how effectively they communicate with muscles. Full-body MRI scans will measure muscle size and quality, and this information will be combined with functional assessments such as walking and balance. Together, these insights will help us determine how motor nerve function contributes to everyday activities in older age. The successful application of this innovative technology will significantly enhance our understanding of how the human motor system adapts with age and how these changes impact everyday function. By identifying the most affected components of the motor system and the motor nerves most susceptible to ageing, this research can inform the development of more effective, targeted interventions. These may include the creation or repurposing of drugs that act directly on motor nerves to improve their function. Beyond advancing research into healthy ageing, these findings will also have broad implications for clinical conditions involving neuromuscular dysfunction, providing new avenues for treatment and rehabilitation strategies.