I've been cycling to work the last 2 years, and now I decided I wanted to switch it up and mostly run it. It's 7km (~4 miles I guess), so twice a day 5 days a week pretty much. Gives me ~70km per week. I've been doing it 2-3 weeks now, goes well.
I ran marathons before - like 3 or 4, usually every 2nd year or so. Haven't done any for about 4 years now and I'm missing it. I've always been between 4-5 hours because although I was very active and I did track & fields before and have always been running say once a week or so, I never really trained for a marathon. I'm 34.
Because life, I don't think I'll be running a whole lot more than during my week. I do other sports as well - I shouldn't need to worry about doing core/strength work (other sports take care of that).
So I'm going to have a fair mileage, but not that much intensity. I mean I can get a few interval in (say on the way back) but 7km isn't a lot of distance to warm-up, cool down AND do intervals. Also don't really wanna get to work already busted.
My question is: would it be realistic to aim for a 3:45 finish with that type of training/background, by summer's end (say 16 weeks from now)? Or am I likely to realize that I would really have needed some amount of higher intensity to really make that work?
Or put another way - how good can your marathon time get with mostly consistent mileage?
EDIT: my current pace going to work is ~5min/km or ~8 min/mile. My watches says I'm around 130-140 bpm. It feels like a good workout but I'm not exhausted and I think I could maintain that for at least 10 miles. I also ran a 10km race last week-end (flat, cool temps) and ran in 44 minutes and felt easy - I think I might have been able to do close to 40 if going all-out.