The great doubling debate - where do you stand?

Really have to sleep in between the sessions or else they don't do anything. Need a life style that affords a nap.

You don’t need to cool down after an easy run of any length. Agreed about the changing and shower adding length to it but can’t fathom why that process would take 45 minutes unless you spend 30 of those minutes staring at a wall.

It might not be so "marginal" if you get injured, which doubling is attempting to mitigate.

Also, some people actually take their running seriously and will do the things that are most likely to bring success.

But hey, keep half-ars*ng it. I'm sure you'll get great satisfaction from telling yourself "I could've run such and such, if I had the time."

The before question is, when should you start to think about doubling?

I would say it's about 7-8h/week of endurance training.

When I worked retail it was

walk 8 hours AM jog 30 PM

That was my theory in HS. I think I was wrong. I think I could have doubled over the summer and did 7-8 hours instead of 5-6. It was a lot easier to recover from a 4&6 than a 8. Given the goal of peaking in HS(running a 15:30 made me all state. Nothing was going to get me sub 14:00), it would have been interesting to see if the 16/17 year old me could have gotten the 70 mpw instead of the 50 I could handle in singles. Granted I am not sure if 10 weeks would have been enough and doubling during the school year wasn't practical in terms of getting enough sleep.

After a 60 min run in these days, even easy, I keep sweating for a good 10-15 min. Having a shower before stopping sweating is kind of pointless, that's what I call cool-down time. I understand that "in theory" one could change in 2 min, shower in 3 min and be back to work in less than 10 min after a run. I may be poorly organized, but In my experience, these 10 minutes usually end up to be 20-30 or more when everything is considered.

Jog 30 in the morning.
Run 90 in the afternoon.

Splitting your day’s workout into two isn’t doubling.

I agree completely. I am not a serious runner. My comment is the perspective on doubling from an old fart that does not lose his sleep anymore about dropping a few seconds on his mile time. I get my ass kicked when I enter a competitive race, and I am fine with that. I run to be fit and healthy and to have fun. I have some personal goals that define "success" and I do not need doubles to achieve them: 6 runs a week plus weights, pilates and cross training is plenty for me.

From a fitness-improvement standpoint, it doesn't matter. Do what is most practical and enjoyable for you, while keeping injury risk low. The science on this topic seems to point that there isn't much difference between doubles and singles, except that doubles might allow you to get more total minutes in without increasing injury risk.

2) 60 am/30 pm

I would definitely agree. However, as a newer (running my 3rd soon) semi-serious marathoner (75mpw) who struggles to get up early enough to fit in 90min before my 8-4, would a 60-30 double provide significant difference over just a 60? Or would doing that twice a week just be junk miles?

Option 4. I have a baby.

They all have there purpose in a good training plan.

I disagree. I think regular doubling has a significant impact on your fitness, both from personal experience and that most serious runners double.

Why would running 90 minutes at once have more aerobic fitness gains than running it in 2 runs??

It wouldn’t. Total nonsense.

Depends on the day for me. Every easy day has a different purpose. Certain days I'll run longer in the morning and shorter in the evening, some days I'll split it evenly and do 60 minutes in the morning and 60 minutes in the evening, and certain days I do it all at once for a long easy run.

I have never seen anything regarding your sweat problem before. Anyway as you noted the OPs question is really meant for someone looking to maximize their training.