I think it really boils down to the individual. I focused on my bike last year and was only running 40km/week. My biking improved and I was told so would my running. Someone that i know was 2nd overall at Cairns IM with a 9.02 and only ran 40km a week, for me running 40km a week and riding 250km+ was the same as if I was just running 40km and no riding. Zero benefits on my run.

As a beginner runner I cannot run 4Ok a week. Just think running only under 8 miles a week fitness would diminish rapidly. I’m not stating my cycling would improve my run but would help sustain aerobic engine. This is just my opinion and could be totally wrong?

There is nothing that says you can't ride before you run. I do this on my short run days, I'll put an hour in the saddle and then go run 3 miles

For me, I need to be very careful with volume increases as the pounding will cause knee issues to flare up, but as long as I increase slowly I'm good. Which is why I'll ride the extra time, then go build the pounding a little at a time.

First - I agree with others that you should avoid a marathon this early on.

The engine is there for fast running, the chassis is not...start slow and build slow. Get in the gym for some strength training. I was able to run well when injured and limited on running by crushing myself on the bike with intervals/power training. When I tried to build run volume, I didn't slow down enough to enable recovery, and it was a vicious cycle of continually thinking I couldn't run more than 25mpw due to injury. I did everything in the 6:20-7:00/mi range (as a low-17s 5km runner), lots of progression runs. Usually a few 4-5mi runs and a hard 8-10mi run on the weekend.

I eventually learned to slow it down, jogged at 8:30/mi for a fall season and got up to 45-50mpw w/striders and transformed as a runner. The price was training alone, b/c none of my friends were willing to run that slow.

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"Don't you have to go be stupid somewhere else?"..."Not until 4!"

I would definitely focus on building up your mileage slowly, perhaps using the BarryP program. As others have said, your engine is well established but the chassis likely isn't. I'd consider gathering at least a year of running experience before training a marathon, in order to prevent any injuries.

I'll add to this, that in addition to the weight bearing aspect of running, running also obviously involves many small but specific muscles in the feet, ankles, and calves/soleus. These will definitely take a little time to develop/perfect.

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- Jordan

My Strava