Working out is the smart choice. A new study reveals that those with a higher capacity for exercise in midlife had bigger brains later. Researchers gave 1,583 middle-aged people a treadmill fitness test, then waited 20 years and tested them again. They found that those with lower physical fitness in the first test had reduced brain volumes later. This, along with another study linking exercise with neuron growth, further cements the connection between healthy bodies and healthy brains — and gives us another shrewd reason to hit the gym.