It is certainly possible to run two marathons three weeks apart. Many runners have done it. And it can be done by running
both hard; both easy; or one hard and the other easy.
The decision to run one or both should be based on three considerations:
How susceptible you are to injury.
(2) How quickly you recover from a marathon effort.
(3) How important it
is to you to run both of them.
Those are factors that only you can evaluate. However, if you decide to run them both,
it should be because both are important to you and you don't have a history of injuries. Otherwise, you should focus on the
one that is more important to you and let the other one go.
If you decide to run them both, you have two choices:
Make one the "target" race and the other either a training race (the first one) or a fun run (the second one).
Run them both as serious marathon races.
I would not even consider running both easily. What would be the purpose of
your entire 16-18 week marathon program?
If you choose (A) above, then using the first as a training run to prepare
for an all out effort at the second is very feasible. Assuming that you use a 3-week taper, the first is ideally timed to
be your last long run before the second. It would simply make your last long run a few miles longer than the 20-24 miles that
most training programs call for....no big deal, especially if you pace yourself properly to simply make it an extra long LSD.
The challenge would be to control your enthusiasm and adrenalin flow that naturally result from a race environment and not
be seduced into running it faster than a good, constructive training effort.
Running the second as a fun run 3 weeks after a hard marathon, would depend on your recovery ability. However, assuming
that you come out of the first without an injury, then finishing and enjoying the second shouldn't be a problem. You should
be recovered sufficiently to run a creditable "race".
Option (B) above, running both as serious race efforts, is also
feasible. I have run back-to-back marathons 2-6 weeks apart seven times. In six of those cases, I ran both marathons as hard,
serious races....none as training runs or fun runs. The seventh time, I ran the first marathon as a very slow LSD, because
I was pacing a slower friend, and the second marathon as a race. I discussed my first five back-to-back marathon experiences,
which were 2-5 weeks apart in 1983-87 during my first running life, in a 1997 post on these forums that was in response to
a question very much like yours. If you are interested, it is on my Running Page at http://mysite.verizon.net/jim2wr/id47.html. My sixth and seventh back-to-back marathon experiences were in 1998/99 during my second running life. In every case, the
second marathon was a stronger, better, and sometimes faster marathon than the first.
From my experiences, I see no
problem with running marathons a few weeks apart....and running both of them hard, if you want to. I admit that I haven't
run them exactly 3 weeks apart. However, I have run them hard 2, 4, 5 and 6 weeks apart. When they were 2 weeks apart, the
second was more of a struggle than the first. However, in every case the second one was a better performance, adjusted for
course terrain, than the first. In some cases, the second marathon was faster than the first.....even on a course that was
more difficult than the first one. For instance, I PR'd in 1984 and 1986 on a Maryland Marathon course that was 10-12 minutes
difficult than the MCM course that I ran 4-5 weeks earlier. The other three times I ran these same two marathons with Maryland 2-4 weeks after
MCM, Maryland was 3-9 minutes slower than MCM, which equated
to a better performance on a 10-12 minute more difficult course. (See my race log on my Running Page.)
My conclusion is that a hard run marathon helps to prepare me for an even better effort a few weeks later. But,
that's me. Others have had the exact opposite experience. Everyone is different. Like so many things in running, there are
no absolutes. The inputs that you get, like mine, mostly reflects either what works for the person offering it or what s/he
thinks works for most people. However, you have to learn specifically what works for you and what doesn't. The only way to
find out is trial and error.
If I were you, I would plan to run both marathons; base my training and tapering on an
all out effort at the first one; run it all out as a target race; run a 2-week "reverse taper" afterwards; then decide whether
to run the second marathon hard, easy or at all....depending on how I feel two weeks after the first.