Effects of Adult Aging on Neural Control and Muscle Fatigue

Individuals 65 years of age and older constitute the fastest growing age group in Canada. With natural adult aging, the neuromuscular system (the muscles of the body and the nerves that supply them) undergo degenerative changes that are characterized by reductions in strength and power due to decreased muscle size. This age-related muscle weakness and overall decline in muscle function is referred to as sarcopenia. Sarcopenia not only interferes with tasks as lifting and carrying groceries, navigating stairs, and performing smooth complex movements, it is highly linked to physical disabilities and risk of falls. Sarcopenia is caused by a decrease in the number and function of motor units (MU), which consists of a single nerve branch and all of the muscle fibres it supplies. During the aging process, some of the MUs die off, while other MUs change structurally to compensate. As a result, there are fewer MUs present, but each one supports more muscle fibers. This MU remodeling process is a compensatory mechanism that acts to maintain muscle strength until a critical threshold is reached and strength decreases at an accelerated rate, usually by the eighth decade of life.

To understand the underlying biological mechanisms of MU remodeling, Dr. Brian Dalton is using a technique called single-unit microneurography. This research tool uses tiny electrodes inserted through the skin and into a peripheral nerve to stimulate and record signals from individual MUs. Using this technique, he will measure the integrity of functioning MUs in aged adult volunteers to determine if MU remodeling impairs neuromuscular function and muscle performance in the older adult. This work will help build a more comprehensive understanding of the neuromuscular system, specifically the process of sarcopenia and how it impacts natural adult human aging. The information gained from this study will aid in the design of functional training programs to improve and maintain muscle function — and quality of life — in older adults.