Movement and exercise are one of the rights of the body. Just as food, drink, and rest are needed to enable a healthy bod to function, regular motion and exertion are as well. In the past, this did not warrant any special consideration. Our ancestors got significant motion just from the requirements of life. If they worked on farms, digging the earth, harvesting the fields, and taking care of the animals ensured enough physical activity. Otherwise, just walking to fetch the daily water or riding a horse was a workout in itself. But times have changed. Many of us can spend our entire day almost sitting in one place and not walking more than the distance of our home to the car in the garage.
Why do we need exercise? In turns out that several of our body systems simple do much better with it
Sources: Spark: The Revolutionary New Science of Exercise and the the Brain, John J. Ratey, MD; Brain Maker, David Perlmutter, MD.