Brain Fitness Aerobic fitness was measured (by VO₂—volume of oxygen expelled after exercise) in 59 children (average age 10, none of whom had ADHD or were pubescent); then the children’s brains were scanned. Overall brain size did not correlate with fitness—genes and early nutrition are more important for that. However, the volume of crucial areas for cognitive control (attention, contextualizing, planning) was significantly greater in the children who were in better shape. This is one more reason to go biking, running, or swimming with your child.