Spark

by John J. Ratey

Population studies bear this out: The most consistent risk factor for cancer is lack of activity. Those who are physically active, for instance, have a 50 percent lower chance of developing colon cancer.

Charles Hillman proved that fit children score better than unfit children on cognitive tests of executive function; Arthur Kramer showed that getting in shape increases brain volume of older adults; and population studies including tens of thousands of people of every age show that higher fitness levels relate directly to positive mood and lower levels of anxiety and stress.

Statistics show that about half of those who start up a new exercise routine drop out within six months to a year.

People with the dopamine variation may have reward deficiency syndrome, which robs them of that rush of pleasure they imagine everyone else at the gym is experiencing.

First of all, daily exercise ramps up BDNF more rapidly than alternate days—at a rate of 150 percent versus 124 percent after two weeks. Curiously, after a month, the alternate-day exercisers had caught up with the daily group.