Cross training on a bike as marathon training?

I'd change Day 5 to a 60 minute tempo ride.

I had (relative) success with low-mileage training -- two runs per week, plus one or two bicycling days. The rides were typically 18-24 miles, at close to full effort, start-to-finish. No significant climbs. Open roads with little traffic, so essentially a TT every ride.

I started training about 14 weeks prior to the marathon, initially to compete in a low-key kayak-bike-run triathlon. After the triathlon, I decided to run the marathon -- only about seven weeks before it. I added a weekly long at that point.

For the 14 weeks, I averaged just 11 mpw running, but had five runs of 15 miles or more, including one 20-miler.

Race day went smoothly, even splits. Finish time was 3:25 (7:52/mile). I was very happy with that, given the low mileage. At age 57, that supposedly "age-grades" to a 2:52 equivalent. I think the bicycling was a key component.

*7 weeks out, added a weekly long RUN, that should be

It's possible this could work. I won't say it's impossible. It would certainly be less boring than grinding out piles of miles on foot.

On the other hand if you're trying to "rest everything that running wears out" during marathon training, I worry about your ability to hold up during the second half of your actual marathon race.

The whole point of marathon training is to condition your body to withstand running 26.2 miles as fast as you can without "wearing out" or breaking down. If you've already decided you can't withstand the training, how are you going to handle the race itself? And if you are confident you will hold up during a maximal 26.2, then have the confidence to do the training.

This is Jim Kiler wrote:

I'd change Day 5 to a 60 minute tempo ride.

That or add some quality into your long run at least every other week. Two hard efforts/week is a good place to aim for you. I don't know that you need to do much quality on the bike. You could sprinkle in some intervals/tempos every week weeks just so you don't go stale but you like biking and it's a way to do something endurance based but easier than running during training. You have a pretty good idea of how to do this already.

I would consider switching day 2<->3. You might might get a little short-strided from cycling for the tempo that could reduce quality. Maybe. The rest seems fine.

biking has pretty strong overlap w/running overall cardio conditioning

You do have to figure out a way to build the 'strength' aspect of running, which is going to require... long runs

which require.... high mileage to not get injured from....

which is what you're probably trying to avoid (or recover from) because you are proposing the bike...

in short... good luck. I'd say youre less likely to get injured on a mixed run/bike program, and can get similar conditioning, but it will be a challenge to get the necessary leg strength for the distance.

bike+run much more appropriate for an injured runner to hit the 5k-half distances imo, if injuries were the reason for biking in the first place.... if not... carry on

I did duathlon at the elite international level for a few years after college and was able to run some fast times. If you’re looking to optimize running performance I’d change the week up like this.

Monday Tempo alternating with 60-90 sec gills early

Tuesday Base

Wed Longer ride

Thursday Base + strides

Friday short ride

Saturday Long Run

Sunday off.

Keep your rides under control. I never got much out of hammering on the bike. Keep the long run long & easy until you can do 2 hrs without issues. I’d alternate Tempo / hills for the first few weeks otherwise you’re going to plateau from things you get from tempo work. Strides / drills are also really important to keep your mechanics good with such low running mileage.

This is Jim Kiler wrote:

I'd change Day 5 to a 60 minute tempo ride.

I would second this. Bike and swimming crosstraining are amazing opportunities to do threshold work with low impact.

I do 30-45 minute threshold efforts... 160-168 bpm. I have been doing these on the bike 2x a week for much of the past year. I feel that they have led me in direction of rapid improvement in fitness.

I would save the long long efforts for running to prepare for the strength needed for the marathon.

Good luck! Cross training ftw. (for the injury prone at least)