As people get older, they often feel less energetic, mobile or active. This may be due in part to a decline in mitochondria, the tiny powerhouses inside of our cells, which provide energy and regulate metabolism. In fact, mitochondria decline with age not only in humans, but in many species. Why they do so is not well understood. Scientists set out to understand how mitochondrial function is diminished with age and to find factors that prevent this process. They found that communication between mitochondria and other parts of the cell plays a key role.