The point is you need to speed to run a good 400. That’s proven and in general elite athletes double up your 200 meter time and add 3.5 second to that time. So for LaShawn if 20 sec is his best, he has the potential to run 43.5 (in his case he has). So unless running 1 hr long runs is going to improve your speed, it does not really matter. So if you have an athlete running 23 seconds the best you can hope for is 49.5 second. There might be some exception to this rule, but it works well for 99% of the athletes. So stop wasting time running 1 hr runs, if that was the case Haile Gebrselassie should be running 42 seconds.