Inactivity begins in childhood, in front of the television and computer. Studies have shown that children who are more active also achieve better academic performance. This pattern continues throughout life: exercise aids learning, alleviates depression, and prevents dementia. Far from being a sign of coolness and enjoyment, too much sitting has become the fourth most common cause of death worldwide. Sitting too much is the new smoking. Those who are inactive not only harm their bodies but also their minds. On a positive note: staying fit also benefits the brain. Erik Scherder, the renowned Dutch neuropsychologist and movement coach, describes the positive effects that physical activity has on our mental fitness—from childhood to old age. He also explains what types of exercise are beneficial at different ages.