For some people, before they get the hang of physical activity, they need tremendous burst of motivation or willpower to start moving their bodies. I am one of these people. I was more excited after my code got running than I myself did some running. This kept me sticking to my chair and fiddling with code. And, initial phase of physical training is not always comfortable or pleasant for a beginner. Benefits will only become obvious if one could persist through some critical threshold. Some people just retract again and again before they could easily "just do" physical exercise. I started to seriously consider exercising after suffering from years of chronic fatigue, which undermined my mind sharpness.