As the body ages, there is a general reduction in the size and power of all muscle tissues. In general, skeletal muscle fibers become smaller in diameter, reflecting a decrease in the number of myofibrils as well as less ATP (adenosine triphosphate), glycogen reserves, and myoglobin. In addition, skeletal muscles become smaller and less elastic. The tolerance for exercise decreases as does the ability to recover from muscular injuries. Much of the decrease in muscle strength associated with aging is due to decreased activity. Strength training among older adults can help to slow such losses.