I hate how much the authors of this article imply causality. >There also, interestingly, was less activity among the runners in a part of the brain that tends to indicate lack of focus and mind wandering. Could it not be that people who have the willpower to run regularly also have the willpower to stay focused? >In essence, the runners seemed to have brains in which certain cognitive skills, including multitasking a…
1) It is destructive to your joints and tendons. Injury rates are very high among runners.
2) It is stressful, resulting in chronically elevated cortisol levels.
3) It is time consuming and boring (of course this is subjective), and very inefficient at improving fitness.