That's not how it works. You get different gains from doing sprinting than from long distance. Your muscle fiber composition, your lactate threshold, your VO2

That's not how it works. You get different gains from doing sprinting than from long distance. Your muscle fiber composition, your lactate threshold, your VO2 max and your economy of oxygen use are all maximized at different distances. For marathon runners, it's the final variable that becomes huge, and you just won't improve that without a solid base of distance running. Even 5k runners, for whom VO2 max and interval work is crucial, benefit greatly from one long run per week (usually around 20km if they're serious). It might surprise you that there's been a general trend in cross-country at the collegiate level towards slower 90 minute daily runs instead of the faster 60 minute ones so popular a decade or two ago. http://runningtimes.com/Print.aspx?articleID=15744 http://runningtimes.com/Print.aspx?articleID=15744 You can lose weight with no cardio at all. However there is a veritable mountain of research that suggests that an hour of cardio per day is good for you. If you can't get that much, some is better than nothing. It doesn't have to be running all the time, either. Playing with your kids or going on hikes will do good for your health even if it doesn't single-handedly take care of your weight problems. Running just happens to be an exercise that allows a particularly high HR and lactate threshold compared to others such as biking, rowing or hiking.