Most balanced plans for reasonably trained marathoners do have two runs 90+min....the mid-week med-long run and the long run on the weekend.  I've been on a plan recommending a third....but it was at a VERY easy effort....and I was running 100+mpw.

 

Runs that long will command recovery, and while they are valuable most will want to split into doubles rather than over-do it and not recover.

I guess I'm doing it way wrong; I'm typically putting at least five or six 100+ minute runs per week and the longest race I will even consider is a half.  That said, I had a blast running in this year's RTB-NH relay with a 6-person "ultra" team (as a last minute replacement), and would jump at the chance to join another ultra team for next year's relay (I was the oldest on the team by 25 years and given my age and relative speed I suspect they'll be looking for someone younger/faster so I probably won't have a spot on this year's team).

You may well be right, that said, I run on trails and now that Daylight Savings time is gone, I'm running after dark with a headlight which in turn means I am running at a pretty slow pace.  At this point I'm planning on adding to the pretty good base I've built this year, getting another 20 or so pounds off my body, and then will worry about speed next spring.

  spaniel is wicked faast - for him a 90 minutes run is a pretty damn long run.   x 10 mile midweek runs  was a pretty comfortable lead into my long run and was solidly in the 90+ range.

90 minute run equals 13-14 miles for me.

 

90 minute run equals 13-14 miles for me.

Wicked fast!

90 minutes for me is 7.5 - 8 miles.

 

90 min training run for me is 6-7mi. Took 4hrs to finish 16 this past Sat long run

This is an example of where one can get in trouble just looking at miles, and ignoring pace/time differences, when looking at training plans.

From a calorie burn perspective, distance is more important than time.  So from a fueling perspective, it's harder for the slower runner to glycogen deplete in training and train that as they have to be out there a perhaps unreasonable amount of time.

However, most of the time we are concerned about the aerobic development benefits.  Those are TIME dependent.  So even if you only cover 6-7 miles in 90 minutes, if the effort is equivalent you are getting similar benefits.

That is something to keep in mind shipo,   spaniel is wicked faast - for him a 90 minutes run is a pretty damn long run.  When I was marathon training it wasn't unusual for me to have 3 x 90+ minute runs a week near the peak and that was only on 50-60 miles/week.

 

Not going to enter the running by time vs. distance debate , but at my best pace, 2 x 10 mile midweek runs  was a pretty comfortable lead into my long run and was solidly in the 90+ range.

My wife is a morning runner who goes out for so many minutes, and then turns around, I am an evening runner who goes out so many miles and then turns around.  As a general rule, she has no idea how many miles she ran for a given run or in a given week, and I'm the reverse, I typically have no idea how many minutes it took me to complete any given run or how many minutes I ran in any given week.

The only reason why I currently know how long it takes me to run my typical 10-mile evening run is that our company is having what they call a "Fitness Challenge" and they've issues us pedometers which track (among other metrics) steps and elapse time.  My night time trail run last Tuesday (the day before I gave blood) took me 1:45 to do my normal 10-miles, bio-breaks included.  Yesterday (when the sun was up and I could see the trail) I was able to finish a 12.5 mile run in 1:50.

From my perspective, I'm not at all worried about running so many 90+ minute runs in any given week simply because my night-time runs are done at such a slow pace they require virtually no recovery.

So answer me this: do you need to practice glycogen-depleted running if your goal race itself is shorter than 90 minutes? Is the point just glycogen-depleting? I was under the impression that you ALSO began using fast-twitch muscles after that time that 'took over' from the slow twitch, and thus, those 90-minute runs were sort of speed training in disguise. I never intuitively understood this principle myself, so explanation would be much appreciated.

I ran my best times in college with only one 90 minute run a week (and about 10 other runs of 40-60 minutes.)

So, I would answer this, for myself, as NO, I do not need many 90+ minute runs to run well at distances up to 10k (and actually too many would be counter-productive).

I think other types of runners with different strengths, i.e. runners with relatively strong aerobic profiles and relatively large training response and good recovery capacity, would need or benefit from more 90+ minute runs.

From the "perhaps rats and people are more alike than we think" category….

From here:

"It was the work of physiologist John Holloszy of the Washington University School of Medicine in St Louis, that showed that continual exercise could put mitochondrial numbers on the increase. He induced one group of lab rats to run on a treadmill for up to 2 hours per day at intensities of about 50 to 75 per cent of V02 max or 12 weeks, while a second group rested in their cages. At the end of this exercise, Holloszy found that the running rats had increased their mitocondrial densities by about 50 to 60 per cent and had also doubled their concentrations of ‘cytochrome c’, a key compound found inside mitochondria which is vitally important in aerobic energy production. Cytochorme c contains one atom of iron per mol and is a power-house of amino acids. Holloszy’s work, at first suggested that Van Aaken’s postulations that the best way to gain endurance was by LSD (Long, Slow Distance) were on the right track. Holloszy pressed on with further research. He had one group of rats running 10 minutes per day, another running for 30 minutes, a third group exercising for 60 minutes and a fourth working for 2 hours a day. Training took place five days a week for 13 weeks at an intensity of 1.2 mph, about 32 metres per minute and 313 minutes for the 10K, which is about 50-60 per cent VO2 max for a fit lab rat. As expected, the 2 hours per day runners had the best mitochondrial development. The 10 minute per day exercisers had about 16 per cent more cytochrome c than the resting group of rats, while the 30 minute ones boosted it by 31 per cent, the one hour runners by 38 per cent and the 2 hour runners increased it by 92 per cent. These findings in 1967 were a potent argument for "Run long, run slow, run gently". Holloszy’s work was given more credence when in a run to exhaustion test, the 2 hour trainers kept going at a good pace for 111 minutes, while the 10 minute trainers lasted 22 minutes, the 30 minute ones for 41 minutes, the one hour rats ran strenuously for 50 minutes. The relationship of a high cytochrome c level to better performance had been firmly established."

Look into it further and make of it what you will.