It is well known that a linear relationship exists for submaximum exercise intensity and oxygen consumption. Most of the increase in oxygen consumption is by skeletal muscle mitochondria for the purpose of producing enough ATP to match the energy needs of the muscle. The control of mitochondrial ATP production in muscle when workload is varied is a complex process and remains a very active area of research. Thus, the purpose of this symposium is to discuss the factors involved in the coupling between increases in work and increased oxygen consumption by muscle. The program will begin with a consideration of the challenges faced by skeletal muscle when attempting to meet its energy demands and the intracellular strategies that have evolved to optimize energy delivery. Next the major control theories for mitochondrial respiration will be discussed. Finally, experiments will be presented that are designed to determine which of these theories are best suited for specific skeletal muscle fiber types. It is hoped that the information presented will increase our awareness of different energy supply-demand strategies among fiber types and how supply-demand strategies are optimized by endurance training.