I think running for 20 minutes will make you better at running for 20 minutes. I'm not a runner at all. I'm average height and built somewhat stocky. I'm slow and likely don't have but average genetics when it comes to distance/cardio abilities. I will however occasionally run a mile or a little more just for the hell of it as I do think it has its place in overall fitness. I do a couple 5K's a years and still rely mostly on sprinting. I'll do a longer run or two at the most as the race gets near. I have no dellusions of winning a race or ever coming close. Its just a good workout doing something different than my usual routine. Its not over the top extreme or I wouldn't do it.