My next marathon cycle starts on December 28 and I have no clue as to what my GMP is or should be. Not that it matters but I plan on using the Pfitz 18/55 plan again. I ran a 5k two weeks ago in 21:03 but that is not a good indicator of a marathon time or GMP.  The question is: should I sign up for a HM on December 21 and race it the best I can to get a better idea of my GMP? If nothing else, I will have an accurate vDOT to give me my training paces. As some of you know I was injured for a while and came back slowly. I want to be smart about training so I don't get re-injured and that is the one thing that is giving me hesitation about racing a HM right before marathon training starts.

Thanks in advance for any comments or opinions.

That would be a good reason to be concerned [in your case]. How long ago was the injury? Have you raced since or even performed quality workouts?

I know when I was coming back from my torn post-tib tendon I used the half maratyhon as my goal race - to measure my speed endurance. I was not fully recovered but I took that into consideration when I began. Three years later when I was healthy that was no longer a consideration and I was able to upshift my HM prep and race performance.

Six months later I managed to tweak the injury just before my formal marathon training was to begin so I was in a similar position as yourself. My concern was stayng healthy and unilke yourself I knew where my fitness was [based on the last half] and my goal [BQ].

If I were you I would ask myself if I'm favoring or concerned about the pre-condition. If so, I would abort applyng that much pressure before you even get started. If you do feel ready then you could consider looking for a shorter race. This would give you insight w/o all the stressors of a 13.1 mile race. You could even do the half but only race to 15k or the 10 mile mark. That to me would be an ideal distance.

Even when healthy and running high mileage I would not do what you're considering - race a half for the reasons given. I've come away from a half marathon as tramatized as I have from a marathon. It's just too much stress to use a time trial, something I'm able to replicate in training with a max workout [or even 7x1000m @ HM race pace is a good indicator of my fitness].

Your 5K race will give you a much better assessment of your vDOT than a HM. The HM will give you a better assessment of your endurance. I think you should race the HM, then compare the different sets of equivalent times and training pace. It should show you where you stand it terms of where your endurance is and what you need to focus on in your training. Looking at your splits in the HM will also be useful regardless of whether you maintain an even pace or not. Depending on if or how much you fall off pace, you'll get a sense of where your tempo pace should be and what pace you should run for those Pfitz workouts designated GMP. (I think the designation of GMP is misleading. Take a look at McMillan's steady state runs. What you're looking for is an extended run at a "prorated" tempo pace. It really has little to do with your goal pace until you get into the second half of the training program when you're starting to get a hint of what might be a reasonable goal time.)

Thanks for the advice you guys. As always, it is much appreciated.

Moth: I was injured four months ago and took almost three weeks off. When I came back I did nothing but easy miles for six weeks and then I started mixing in Daniels speed workouts twice a week. Intervals and stuff... I ran a 5k two weeks ago and got a 21:03. I wouldn't say I am concerned with my previous condition, but it is in the back of my mind.

I just looked at race website again and there is also a 10k that day. Would that be a better choice?

wc: Something I forgot to mention was that I have not yet run 13 miles since coming back. My longest run has been 11 and I was going for 12 tomorrow, easy pace. You are right, though. A HM is a better indicator.