I ‘m a second-year triathlete in my late forties. I’ve done a few sprint triathlons and a couple of Olympics this year. I ‘ve done little enough running outside events, but I can knock out a 21 min 5k or 43 min 10k as I stand now. I ran eleven miles last night at nine-minute pace and entered the Dublin City Marathon at the end of next month. How best can I utilize the four or so weeks I have left til Dublin? I am going up mostly for the experience; I want to give the marathon a real go next year so will use this one as a dry run. That said I feel I could run pretty well and want to safely maximise my performance.
Your 5 and 10k times are very decent times, to be honest. You have one advantage by doing a triathlon, you have built up some endurance fitness. A sprint triathlon is about a half marathon and an Olympic triathlon is about 3/4 of a marathon.
While they are a different type of fitness it will help and I would say you need to a long run once a week for three weeks, so maybe 13mile, then 17 miles and week before the race 15mile.
On the side of your main run do a recovery run after each long session and then a few pacing run at marathon pace between 6miles to 8 or even 10 miles if you feel like it. this would be 3 to 4 run a week (1 easy, 1 long and 1 or 2 marathon pace but on a shorter distance about 9mile/h of 8 if you can)
Let me know how you get on