I have been running all year around 20 miles a week and would like to complete a marathon 8 weeks from today. Do I need to start logging more miles per week? I have ran 3 half marathons this year with my best time being 1:37:00 and slowest time of 1:41:00. I would like to run the marathon under 4 hours. I usually complete a long run on the weekends but have never ran over 15 miles at one time. What do you think. Thanks for the help!
Let me say one thing up front. You can't really compare a half-marathon to a marathon. The marathon is a lot more than twice the distance. OK, I would say that if you can get a 20 mile training run done within 5 weeks, with a general increase in weekly mileage, you should be able to finish. But it may not be easy or pleasant. Whether you can finish under 4 hours is anybody's guess. I had run a 1:45 half before my first marathon and it took me 3 tries to get down to 4:17.
Len is right - a marathon is more than just twice the distance.
But what the heck, your genetic makeup and general fitness level may be such that you'll have no problem pulling this off !
Work up a plan that get's you to a somewhere close to at least one 20 mile training run at least 3 weeks before the marathon. Don't fixate on your time, just work on building up the distance and not getting hurt. It doesn't matter if you do it at a 9 or 10 min/mile pace, just make sure that you build up your endurance. Build up your miles weekly up until 3 weeks out and work on not injuring yourself. Then on marathon day, start slow so that you don't burn out early, and if you are feeling good you can turn on the jets after mile 14 and scream home to the finish line.
I too have run a bunch of HM, and run 13-15 miles on weekends just for kicks, but things seem to change physically when you get to mile 20/22... It's hard to explain. You'll see.