Half marathon on tired marathon training legs?

Obviously, on tired legs, one would not plug that Half time into Daniels’ Calculator to get an ‘equivalent’ Marathon time. Some athletes use an untapered Half 3weeks out to run close to the expected pace in the goal Full.

Thank you so much, this is so helpful!

I've only ever run three halves. My times were 1:37 (trained but this was conservative), 1:33 (on tired legs amidst a marathon training cycle), 1:35 (most recent, ran into the wind for at least 5 miles and had tested positive for covid 2 weeks earlier so definitely still recovering). I've run two marathons. My first was 3:26 (super flat and I was feeling healthy) and my second was Boston 3:28 (for this one, I was getting over a cold).

All of that said, I haven't the best experiences, but I would just use the 1:37 as a predictor, especially since it's your first marathon. Also, those calculators (imho) are way optimistic.

What is your marathon target and what sessions did you do the week before? I am running a half soon and will be tired going into it from the marathon block, so curious to hear what you expected to run.

I'm aiming for a sub 3:30. All of my training so far indicates this is possible... The week before the half, I did a 20 mile long run and a 10 mile speed workout (10x400 + 1xmile), and only took 1 rest day the day before the half. What about you?

Same here and I would say the 1:37 points to a more than possible sub 3:30 no (specially if you did those workouts before)? My HM is in 2 weeks.

oh awesome! good luck with your HM and marathon!!

A half in marathon training, without a taper, can wind up being very, very close to marathon pace. When I'm in marathon training, I'll stick a half anywhere from 4-8 weeks out. I like to do something like 10 @ GMP + 3 faster because I know I won't be able to roll anything faster. It all depends how your effort feel. Did it feel like you were racing the half or did you cross the finish line feeling like you could have handled the pace for a lot longer?

Running faster than goal MP for a half during heavy training is a good sign. I'll second NERunner than even if you only hit MP, there's no reason to panic. I ran a humid 20k 3wks out from my goal marathon last year and it ended up being just a hair quicker than what I ran in the marathon.

We don't have enough info to give you a full answer, but I'll just give you my scenario...
I'm running a full in just under 4 weeks. Planning to do a half marathon one morning this week at goal marathon pace. I don't expect it to be ALL out. Hard but not insane. As long as I feel decent and HR stays under control throughout the effort, it'll lock in my goal pace for race day.

Question for you is: did you go ALL out for this? If so, I'd add a couple of minutes to your finish time and use that new time as your goal pace for the full. If you finished this feeling like you didn't really race all out, perhaps you can use this time and just double it for when you are tapered and ready to roll.

All that to say, not knowing how you approached this HM leaves us without enough info to help.

Cumulative fatigue can drastically reduce race performance during a heavy training block. I just ran a half marathon this weekend and I went into it overcooked in my training. 4 races in 9 weeks. Speed workouts every third day which in retrospect I ran way too hard, near race effort too close to the race. I didn't realize I was doing it until I felt super flat and drastically underperformed on race day, compared to where I know my fitness actually is. My goal marathon is many weeks away, so I'm not going to worry too much about it and neither should you.

If you didn't taper, don't bother plugging the result into any formulas. You won't get a valid result. Consider it a great tempo training run that will pay off on race day and make sure you don't go into your marathon overcooked, like you were for the half half-marathon.

I ran a 5k all out, in the middle of my highest mileage week with a morning workout as well. That ended up being my 8k pace when I tapered for my peak.