Go for a Walk
Taking a brisk, 30-minute walk three times a week doubles your capacity to make energy, Dr. Merrell says. "Literally, these energy factories in the cells called mitochondria can not only increase in size but up to double in number just by brisk walks," he says.
A "brisk" walk means raising your heart rate to your target heart rate or to the point when you are breathing rapidly but can still hold a conversation. Calculating your target heart rate is easy: Subtract your age from 220, and multiply it by 0.7.
"Just 30 minutes of this type of exertion creates energy and sharpens your mind," Dr. Merrell says. Also, researchers at the Neurotrophic Lab at UCLA found that a molecule responsible for brain plasticity, which aids in quick thinking, is elevated for a full day after a session of moderate exercise.