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DroppingDead, even if you were once accustomed to running 6-8 miles at a time, taking several months off means that you'll need to start back slowly.  You at least have the advantage of youth.  The arch soreness could be too much/too soon, altered gait due to the blister problems (good to hear that you have it under control) or just simply inappropriate shoes.  Several years ago, everybody in the trail ultra scene loved Montrail Hardrocks, and to this day I have never worn anything that have made my arches hurt more than those damn things.  One way or another, you'll figure it out.

Where did you get this formula?  I'm impressed!!  This is not bad at all!!

Being obsessed with numbers, it is easy to make stuff up.  My favorites are the ones that supplant a complex calculation with a simple rule of thumb.  That is somewhat the curse of physics, being able to produce a plausible estimate based on the simplest rule, knowing full well that the right answer doesn't really exist.

Here's another one:

For a conservative estimate of marathon potential, take the minute/mile pace from a 10K race in minutes:seconds and divide by 2, to get a predicted time in hours:minutes.   Most calculators predict times a few minutes quicker (e.g. 2:55 vs. 3:00 for a 6 min/mile 10K race pace) but I think it is a better rule of thumb for first timers than calculators or Yasso 800s.  Most people race a 10K leading up to the marathon and it is more endurance specific than 10x800m.  You'll impress people when you can give them a round number time estimate right off the top of your head, instead of fumbling for an iPhone app.  But still, it is just a number...

Pretty crazy.  Just plugged in my last 10K into your tough formula (7:56 pace) and it spits out 3.78 hours which comes out to 3:46.

Running my 10K results through Daniels Calculator is gives me....  3:46:25.  McMillain gives me.... 3:51:18.

I think on slower runners your simple divide your pace by 2 ends up a little more aggressive, but still pretty darn close.

On the easy pace, I ran a 6:55 mile for the first mile of my 5K Saturday (and then blew up because it was way too fast of a start) and if I take that times the square root of 2 I get 9:15 for my easy pace.

Daniels Calculators shows an easy pace of 9:35 for a 6:55 mile and McMillan shows a big range from 8:54 to 9:51 for an easy pace based on that mile time.

Still not bad, but maybe a little more aggressive for slower runners on the easy pace calculation.

Age: 49 Weight: 202 Height: 6'3" (Goal weight 195)

Current PR's:  Mara 3:14:36* (2017); HM 1:36:13 (2017); 10K 43:59 (2014); 5K 21:12 (2016)

Here's another one:

For a conservative estimate of marathon potential, take the minute/mile pace from a 10K race in minutes:seconds and divide by 2, to get a predicted time in hours:minutes.   Most calculators predict times a few minutes quicker (e.g. 2:55 vs. 3:00 for a 6 min/mile 10K race pace) but I think it is a better rule of thumb for first timers than calculators or Yasso 800s.  Most people race a 10K leading up to the marathon and it is more endurance specific than 10x800m.  You'll impress people when you can give them a round number time estimate right off the top of your head, instead of fumbling for an iPhone app.  But still, it is just a number...

I love it.  A formula that is basically invalid, but works in the range in which humans are likely to fall.

Npaden, I think your math is wrong.  If your 10K pace is a teeny bit under 8:00, then this predicts a slightly < 4:00 marathon.  That is significantly longer than Daniels or McMillan.

Well at least someone here is making relevance to the subject. - S.J.

I just divided 7.56 by 2 and got 3.78.  Then I multiplied .78 by 60 to get 46 minutes.  I guess I soiled myself mixing seconds and minutes and hundreds.

I guess I could just divide the 56 by 2 to get 28 and add 3:30 to that to get 3:58.

I hate the 60 seconds and 60 minute thing.

Age: 49 Weight: 202 Height: 6'3" (Goal weight 195)

Current PR's:  Mara 3:14:36* (2017); HM 1:36:13 (2017); 10K 43:59 (2014); 5K 21:12 (2016)

an amazing likeness

A 10K is <25% of the marathon distance....does it qualify as a good predictor...I'm skeptical.  To my (limited) experience, a few different half marathon times...over a range of training quality, race conditions, mental prep will serve as a good predictor for only the first 20miles - you're on your own for the last 6.2.

I've done my best to live the right way. I get up every morning and go to work each day. (for now)

I just divided 7.56 by 2 and got 3.78.  Then I multiplied .78 by 60 to get 46 minutes.  I guess I soiled myself mixing seconds and minutes and hundreds.

I guess I could just divide the 56 by 2 to get 28 and add 3:30 to that to get 3:58.

I hate the 60 seconds and 60 minute thing.

Yeah, colon vs. decimal point.  With a formula like that, either method might be right (equally invalid).

Well at least someone here is making relevance to the subject. - S.J.

A 10K is <25% of the marathon distance....does it qualify as a good predictor...I'm skeptical.

Right, but that's true whether you plug your 10K time into McMillan, Daniels, or Seilerts (congrats, Scott, for joining them).

Well at least someone here is making relevance to the subject. - S.J.

Sorry, I should have included the caveat that dividing time in half isn't the easiest thing.

But the whole point is, formulas and predictors are just someone's average, or even just a set of arbitrary rules, with an unpublished error that is highly asymmetric (you might beat the time by a few minutes or blow up and be off by an hour).  Just take them all with a grain of salt.

A 10K is <25% of the marathon distance....does it qualify as a good predictor...I'm skeptical.  To my (limited) experience, a few different half marathon times...over a range of training quality, race conditions, mental prep will serve as a good predictor for only the first 20miles - you're on your own for the last 6.2.

of course, the closer the distance to the marathon, the better the prediction. However, if you really race a 1/2M, it can be quite taxing on the body in terms of recovery. The recovery period can be disruptive (especially the older we get). My coach suggests nearly 2 weeks for a full recovery from a hard raced 1/2 marathon -- and based on my experience I agree with that.

I think a 10K can be a great marathon predictor if you do it in the middle of marathon training plan, and you don't run it on completely rested legs.  All of those predictions have (or should have) the disclaimer that the prediction for other distances is assuming you're doing the training for that distance.