Fastest way to improve aerobic base without overtraining?

Doubles. Just 2-3 miles each morning will do it.

Winning is fun.

Cross training is good but it depends from what is your preparation in those sports. I know in my training group people that cross training on a regular base with great results. One guy now 53 he just run a 2:59 in Rome marathon (very near his 15 years old pb). He run no more than 60 km ( about 38-38 miles) a week . He use to swim since years once a week 2 or 3km about 45 /50 minutes. But what makes the difference is what he has done in the last 4 years . UTMB , Ironman , Ultra trail of 50 or 60 km . Some Marathons at a confortable pace about 4'30/km or slower . The key is consistency , and of course to have a body that dont get injury. Another lady 44 years old use to cross training with bike once a week as a relax day, she 's an ex bike pro . Anyway last november she did his marathon pb with a 2:42 in Valencia . A great talent since she just begun to run a few years ago. And every year she use to run 4 or 5 marathons from 2:42 to 2:50 . She 's able to do this with about 100 km /week so about 60 miles. She doesnt have any speed (HM pb 1:19) but she can read newspaper and drink tea at 4'/km pace. This to say that if you already have an history in some sport like swim or bike you can use a day a week to relax. But if your goal is a marathon you need to run there s no shortcut. Using bike to increse aerobic base it needs a lot of time . About 3 times more than the time you need running and in any case you are not training your specific athletic gesture.

Thanks all for the insight. I agree that running-specific training is the most ideal. And I agree that aerobic strengthening includes strengthening the muscular system, with some muscles only targeted by running. I suppose my question is about generally strengthening the cardiovascular system. Obviously, biking 75 minutes is not the same as running 75 minutes. What I was referring to was the effect on the heart as being similar if completed at the same heart rate. Would not both activities have much of the same effect on the cardiovascular system if they were completed at the same heart rate zone? Am I missing something?

Not surprising. There is a HUGE amount of crossover between speed skating and cycling. Eric Heiden switched to pro cycling after his olympic skating career.

probably because of the rampant unchecked doping?

Training for a marathon by mostly biking will likely go poorly. As others on this thread have said, you need to train your muscles, bones and tendons to handle 26.2 miles. The bike will not do this.

Serious question, what is the reason that you signed up for a marathon if you don’t have time to train for it? Could you switch to the half or 10k instead?

I use my bike on a trainer, sit in an upright position with bent elbows, warm up and hammer it. Heart rate whatever, alternating with running. I think your instincts are right on. Injuries are game over.

The title of your thread says one thing; you say something very different in your initial post.

> In your thread title, you indicate you want to improve without over training.

> In your initial post, you say you do not have the time to run more.

There are individuals who will suffer injuries if they run three days in a row or more, no matter how slowly they run.

There are individuals who will suffer injuries if they run more than 15 miles per week, no matter how slowly they run.

For individuals who cannot run much but want to improve fitness quickly, cycling &/or swimming &/or Nordic skiing help but an individual who chooses to cross train by cycling or swimming or Nordic skiing will not commit fewer hours to fitness per month.

there are no shortcuts in our sport my friend, sorry to break it to you

I'm guessing that many of the people commenting on this thread have never actually tried cross-training, or at least never tried it seriously.

There are huge gains to be made, especially for people who are susceptible to load injuries.

They seem to have it in their heads that riding the bike involves simply spinning your legs over at 1.5 w/kg.

It doesn't.

Your vo2 max is your vo2 max, regardless if you improved it on a bike or through running training. Same goes with Lactate threshold.

If you simply do hard running training, you can maybe do 60-90 minutes at or above Lactate Threshold each week. If you supplement with the bike, you can do twice that.

Can. You. Read.

The OP wrote: "I don’t think I can feasibly get back to that quickly without risk of some injury or overtraining."

H I L L S

Fair enough. Though I imagine I can find enough “time under tension” for my muscles, bones, tendons over the next 5 months even with cross-training. I suppose I’m wondering if anyone has experience using the bike to get a jump on training, before fully switching to a running-only focus. Let’s say, two months with cross-training on an elliptical, three months just running. Would that provide the average runner enough time to get back to comfortably handling the load of 70+ miles per week if one is only averaging 20 right now and a few years removed from heavy training? I’ve at least been consistent working with weights to strengthen injury-prone areas. I’m sure that it’s quite different for everyone and there are many factors to consider, but is it reasonable? Mostly injury-free right now, but I want to be cautious.

To answer your question, the race has been a big bucket list goal for several years. It was cancelled three times during the pandemic, and I had to miss the return of the event last September. I signed up around then before life got extra busy 😃. No switcharoos allowed.

Yep, you’re right. The omitted detail is that I’m working on reorganizing my schedule to allow the increase in training. But there isn’t much time, in my mind, to get back to the weekly load I want to handle, unless cross-training can help — which is the question. “Faster” is used because I imagine I would need more than five months to get comfortable with 80mpw + workouts if I were to only run.

I would argue the ONE thing you can compare is the CV workout component? You max out your stroke volume relatively early in a run or bike...very early (which is why easy runs work). Once that is maxed your HR goes up to pump more blood. 150bpm is 150bpm? I also notice that indeed biking requires way more effort to get to the same BPM.

Why do you believe that your cardiovascular system needs strengthening?

I think you can do this as you suggested (use both running and cross training for a couple months, then focus on specifically running for the 3 months leading up to your marathon).

I think some keys for you would be:

1. Continue your lower body and core strength training, at least in a maintenance mode, to help prevent injury.

2. Focus more on the Big workouts than on total mileage. A previous poster on this thread stated the importance of specifically depleting your running muscles (glycogen depletion).
That's what your longer, marathon-specific running workouts will do. While over the long-term total mileage can lead to big positive changes, with your limited time I suggest that you focus on doing a longer, glycogen depleting session once every 3-4 days (a couple days/week). Between these longer specific workouts, keep your runs shorter and easy. So basically, do a longer session (possibly with some quality aerobic paces), then run 2-3 days shorter and easier, then hit another big workout.

This should be a pretty safe, and effective way for you to run as well as possible with limited time.

Have fun!

My heart rates and effort level have slways been the same, biking or running. Maybe you're just weak at one compared to the other?