I do 2 hours of activity per day (cycling, walking, swimming, etc). More in a summer. Since in winter it is more or less routine I just work when I do it. Usually solve some design / programming / planning task which I will implement later when at my desk. Over many years it has become a habit. Sometimes when I come back home for a walk I can't remember a thing about outside because my legs were doing on work and the brain was busy with the other.