What is your goal for the marathon? How many miles/week when your foot started to hurt? How much running history do you have prior to this? What is your training pace for most of your runs? How many miles on your shoes? Age/weight. Lots of factors that can influence this.

If the injury popped up out of the blue after an 18 miler, running anything that long again before the marathon is a recipe to miss your goal race. Your're way better of to start your taper early and show up to the race in a condition where you can actually run the race.

Firstly you need to find out what the injury is. Just because you don't have swelling doesn't mean its not a stress fracture!

In my experience going to a good running specialist physio is always worth it, and if it is just tendonitis you need to find a way of eccentrically loading the tendon in question, not always easy, as this is the only thing likely to help the tendon recover in the time scale required, but you really need to know its not a stress-fracture before you do this!

With time scale before race in mind and the fact you still have pain, I'd scrap the old plan, sounds like you've already missed a large part of it anyway? My advice would be to rest now, get the injury sorted and workout a two/three week progressive build up of training to get you to race day in a healthy condition! I'd say start with a 2 to 3 mile run and build from there. A max length run of 15 miles the week before would be a good aim...but no more and maybe less!

Good luck.

Na don't do the 20 or do it at a very very low intensity if you want don't feel like you need to tho. You can run a marathon very well off interval training alone doing like 15miles a week it's not like a 20 mile run is a magic workout. There's many ways to do well but just sleep a ton, eat a lot, and relax. I personally would continue training but at a very low intensity until it feels better not that that's a good idea but I would do that. 18 miles is pretty much 20 anyway. I don't focus on a single workout too much it's more about total training load

Thanks for the input everyone! I'm 29, 5'10'' and 200 lbs. I was an athlete in high school/college but only started running again in mid-2014. Since then I've done a few sprint/olympic races and a 70.3 last November. This would be my first marathon. Following the Hal Higdon program I was running around 30 miles a week. I did the 70.3 at 9:45 min/mile and was shooting for a 10:00 min/mile marathon pace. I usually do my LSD run at 9:30-10:00, my short runs around 8:00 with 7:00 intervals, always depends on the distance. I've had to ease off the intensity at times because of various aches and pains. Interestingly I was doing a lot of PT for an injured FHL tendon (strengthening the tibialis posterior tendon and doing a lot of calf raises, stability exercises, etc.-I'm getting a bosu ball after this recent injury!]), which had almost completely recovered. As for shoes, I used the ones I raced in for the 70.3 for the first few weeks of marathon training as I broke in a new pair. And I really didn't feel anything in this spot of my right foot until after the 18 mile run. I was actually totally fine during and after the run but at work the next day I developed a limp.

Today it's not great. I'm mentally preparing myself to not be able to do this marathon. This is the hardest part about triathlon. But the best part is that there are two other disciplines to focus on now!

Sounds like you are running too fast -- you've basically run all your runs faster than (marathon) race pace. If you look at Hal Higdons other plans he specifically calls out "pace runs" which is running at your goal marathon pace. Those are typically 1 run a week and less mileage than your long run. Couple that with maybe 1 interval session a week. Your long runs should be 30-60 seconds slower than your goal marathon pace so for you 10:30-11 min miles.

What he ^said. Go to McMillanrunning.com and use their race predictor to get your recommended training paces based on a race result. Too much intensity will definitely cause problems for newish runners, especially w/ you being a bigger guy. I'll hit 40 this year, usually run 40-50 mpw unless doing a build for a marathon. I only do 1 quality run per week, the rest is at my easy/long/slow pace. I ran a 3:07 in March off of a winter of nothing but base miles on a treadmill (70 per week though). I'd skip the 20 miler and see how you feel during taper. Some time off can do wonders and you won't lose much fitness. Also, for me, adding 10% mileage per week was too fast when I trained for my first marathon and led to problems. 1-2 per week max with a short week every 4th week seemed to help a lot.

Thanks again for all the input. Here's an update...

I saw the physical therapist, who's helped me through injuries before so he knows me well. He confirmed that it is the peroneal tendon and he is positive that it is not a stress fracture (the pain is there when I walk and when I jog, but if I sprint it disappears). For some complicated biomechanical reasons that I won't try to explain here, I need to strengthen my soleus muscle to prevent my arch from overexerting the peroneal tendon. I was doing standing calf raises to strengthen my gastrocnemius, but apparently these exercises don't strengthen the soleus as well. To strengthen the soleus you have to do seated calf raises (with weights over your knees; there's also an exercise machine that does this) or calf raises with your knee bent, which are pretty difficult and tend to work the quads just as hard.

I'm still hoping to do the L.A. marathon. I just needed a bit of strengthening to get rid of the pain. It'll end up being a two week workup off of three weeks with basically no running, with mileage looking something like this (Week 1: 3-6-8-12, Week 2: 4-6-2-marathon). If anyone thinks this sounds crazy, let me know ;) Plus side is that my physical therapist is working the marathon near the finish, so if I'm in bad shape I can at least consult with him on whether or not to finish.