Grant: Travel Awards - Institute Community Support

Skeletal muscle growth and maintenance is governed by a population of resident muscle stem cells, termed satellite cells. The gradual loss of muscle mass and strength with aging is followed by the loss of muscle performance and function. The age-related decline of type II muscle fiber size is known to be accompanied by a type II muscle fiber type specific loss of satellite cell number and function. Growth factors found in the circulation are important in the regulation of satellite cell activation. We examined the distance of satellite cells to capillaries at rest, and in response to a single bout of resistance exercise in healthy older (n=22) and younger men (n=23). Fiber-type specific muscle cross sectional area (size), satellite cell content, capillary content and distance between satellite cells and the nearest capillary were determined. Type II muscle fiber size was smaller in older compared with younger men and was accompanied by a lower number of satellite cells. Type II muscle fiber capillary contacts and individual capillary-to-fiber ratio was lower in older compared to young men. For type I-associated satellite cells, there was no difference in distance to nearest capillary between young and older men. A greater distance was observed between type-II associated satellite cell and the nearest capillary in both young and older men. Interestingly, this distance was greater in older compared to young men. In response to a single bout of exercise, we observed in both older and young that activated SC were situated closer to capillaries than inactive satellite cells. Our research highlights the loss of muscle mass (specific to type II muscle fibers) seen in aging, which may be a result of a greater distance between capillaries and type II muscle fiber-associated satellite in older compared to young men. In addition, active satellite cells are situated within a closer proximity to capillaries in response to a single bout of exercise.