I am currently training for my 2nd marathon (I am slow , first was a year ago in 4.52) In preparation for this one I have been told that the long runs of 4 hours is a waste and that I should run for 3 hours in the morning then 10 k later the same day. Has anyone heard of this approach? I am worried that I won't have any 20 mile runs under my belt. Should I be worried?

I'd go for the 20, no matter how long it takes. Waiting until later in the day to do the final 10K probably won't make much of a difference anyway; for a training run, it'll be slow.

There are two different schools of thought about this which are diametrically opposed... One school says that running for too long causes a great increase in the chances of your getting injured. When you are injured, you are forced to stop running and might not even be able to run your marathon. Even in the case where you are not injured to the point of not being able to run, you may be so hammered that you are not able to effectively do any of your other weekly workouts. So in this case, they believe that it is better not to run too long, and many experts say 2 1/2 hours or 16 miles is usually good enough (whichever is less). Another school of thought says that if you are not trained to spend the time on your feet required to complete your marathon, then come race day, you will find it very difficult because you are undertrained for the distance. So following this train of thought, if you want to finish a marathon in 5 hours, then maybe you should get used to being on your feet for 4 to 4 1/2 or even 5 hours at a time to train yourself for it. If you are only out there for 2 1/2 hours, then you will be unprepared to be out there for twice as long on race day. Everybody is different and often we respond to the same training in different ways. Also we may have different goals. Did you run 20 mile training runs for your first marathon, and if so did you feel that it helped you? If so, then maybe you should keep doing them. If on the other hand you felt like the 20 mile training runs hindered your training the other days of the week, then maybe you might benefit from changing up your training strategy and seeing if you get the results you want. Finally, not everybody is motivated only by the results. I personally enjoy running, and I like running more than 20 miles at a stretch. So I wouldn't train any other way. But if you find that you hate running that long, then don't do something you hate because life is too short, y'know?

I actually tried this one year and I didn't feel it worked well for me. I tried running the 13-15 miles a bit on the faster side than I would normally do a 20+, thinking it would improve my speed. Then I would go out for 5-8 miler in the late afternoon/early evening. My overall marathon time was not where I thought it would be. Around 21-22 I really started having a tough time, quads tightened up, calves were getting very sore, and I really ended up doing a fair amount of walking. Since then I have done 20+ in one shot and never had the problem again. We are all different, so your training may vary