Physical Fitness and Personality

I think there is a strong likelihood that some percentage of personality is an artifact of your physiological health with high physical fitness correlating to higher emotional stability and more optimal brain symmetry. Physical attractiveness is also likely highly correlated to fitness (body symmetry research as well as common sense supports this). The more unfit you are the higher your resting heart rate and potential cortisol levels. Cortisol is a fight or flight chemical which if over produced inhibits mental functioning and increases the chance of a heart attack. There are numerous other chemicals that your body over or under produces when you have reduced fitness.

While any type of regular exercise will yield some benefit, I think based on the research I've read that aerobic exercise (endurance training / lighter more prolonged exercise) is better than anaerobic exercise (strength training) as it makes you leaner while increasing the strength of your heart. Aerobic exercise increases slow wave sleep (the deepest, most restorative part of sleep) and heart rate variability (which correlates to reduced mortality risk), anaerobic exercise does not. Having a strong heart is more important than being able to lift 500 pounds, which is maybe why the world is run by people like bill gates and not polar bears. I do think some strength training (like pushups) is important.

Running is one of the best aerobic exercises. A recent study in the Netherlands found that frequent running reduced mortality by a factor of 3.0 (frequent walking only scored 1.4). Based on the research I've read 36 hours is the optimal recovery time between runs. Provided you run at least 30 minutes, speed becomes more important than duration. (more info)