What is the best workout for when you train for ultras?

Practice eating lots of snacks, and praying for "trail magic"

Google David Roche's training videos, and whatever he does, don't do.

More serious note, as others have said, long slow runs, with elevation (especially if it's a mountain race) gain and loss. Also, practice walking at a 15 minute pace (yup, LRC track snobs, we actually practice walking), and don't forget to work on your nutrition plan. What works in a marathon may have you bonked at mile 80, since your stomach might be going "no more gels" by that point.

Ive found success with binge eating while walking, great race simulation.

And try to stay on your feet for the rest of the day (don't collapse onto the sofa afterwards).

Alternatively, my go to workout is 10 * marathon at 50 mile race pace (only joking 😃).

i discovered trail running in my early 40's after previously running xc in high school and college. i was slow though. ran road races and a couple marathons during that time. spent 8 years racing pro/expert mountain biking just before i started trail running. i continue to do it low key also. i ran 5 or 6 hundred milers, including western states a couple of times. never liked the distance though. so i never did back to backs. too sore and tired for the next day to double and didn't want to spend the second day slogging and walking. no interest. so i would do a single long run of about 30 miles, if doing a hundie. with about 6000 elevation gain. used a 50k -100k prior as prep. sometimes i would do a mid-week 20 miles also, but rare. never did tempo's or speedwork as i was just doing it, "for fun". so you should be fine doing s couple long runs if you're doing it just to finish. if you're doing it with marathon training and just increasing the long run, you will be fine as marathon training teaches your body good running economy.

Older ultra guy here

Assuming you’re doing a race with at least 15,000 feet of elevation so you can get the most bang for your buck

obviously lots of mileage like others said, but the biggest things that are going to make a difference are

1. practice eating real food during training runs

2. learn how to manage blisters

3. practice steep incline and decline on trails

I’ve seen these three account for most drops

Also, I know people generally bag on ULTRAS and chalk them up to an easy walk, but don’t underestimate the time or distance because depending on the race you may find yourself alone at 3 o’clock in the morning in the woods, hallucinating with diarrhea, a rolled ankle and some blisters wondering if that black bear is hungry

have fun

I don't know much about what the elites are doing, but from a scientific standpoint I would think most easy days should be run at race speed to build best possible running economy. One hour a day is sufficient to build running economy if you are already slow twitch. I would add an hour or two of cross country skiing/roller skiing to improve the body's ability to utilize fat as fuel.

Those "hard" easy days may also affect your workouts so those should maybe not be as challenging as for shorter distances. Hill runs at different intensities once a week and one lactate workout a week at the maximum. Some weeks should be back to back long runs, but I don't think you need as many of those as others may think

People only do ultras to impress non runners and because their half and full marathon times suck!!

I imagine Jim Walmsley, Matt Daniels, and Des Linden would agree.

I'm not talking about the 0.1% of ultra runners...

Have ultra-runners tried something along the lines of doing two long runs in the same day? For example, 20 miles in the morning and another 20 miles in the evening. I feel like this would be the logical extrapolation of a Canova special/specific blocks, especially if you implemented some kind of carbohydrate depletion for the PM session.

According to Chris McDougall in "Born To Run", Ann Trason would run double long runs as part of her normal running schedule

Ankle weights.

David or maybe Seth is that you?

if you are a 100 mpw guy, you can do ultra

cut back on the pace to very easy

take frequent breaks,

don't let yourself get tired at the beginning

absorb nutritional gels, and tweak in practice in the 5 min breaks or whatever.

get some anti blister patches.

you can go all day

for competitive, well, follow an ultra schedule

the idea that you run 200 mpw or some such, your endurance goes down with very long efforts too often.

^^^This (and the comments from "darkcloud" and "Blister boy").

I quit the 100s after three (Bear, HR, UTMB) largely because I'm not built for them, and it's hard to top the UTMB experience anyway. I went in with typical track and cc, then marathon and shorter trail-race experience, and basically followed the same training volume as I would have for a mountain marathon. Beyond that, and especially for your first outing, you're risking injury and/or excessive fatigue for very little incremental gain. Far better to focus on the other aspects everyone mentions such as fueling, hydration, and etc... as that's what gets you to the finish line when everything else goes to h***. And trust us, it will.

This!
People make the mistake and think if they can do 100 mile weeks they can do a longer ultra with no problems. That is not the case.
Ultrarunning is about crisis management. Weather, blisters, heat, getting lost, running in darkness, chafing, nutrition......
You need to learn to manage all of these things. So ideally you learn them by doing ultras. Start with shorter ones and work yourself up the distances. 3-5 years in, you can start planning a 100 miler.

You can have everything planned out on a spreadsheet but ultrarunning really starts when sh!t hits the fan, you have a bunch of problems in the middle of the night and you keep going. Others quit, you keep going.

That's the difference between a 100 mile finisher and David Roche who quit after 60 miles because he wasn't feeling it. Guess what, nobody is feeling it at mile 60 but the experienced runners just keep going anyway.

Test

"Crisis management" FTW!

Personally I skipped right over the shorter ultras and dove right into Bear, but with a major twist: I paced Hardrock for 40+ miles several years in a row beforehand. Those experiences - running overnight in the back half of a 100 with guys who were doing it, the whole IT, were invaluable. Living, breathing... suffering their journey up close and personal re-shaped my understanding of the true grit required to finish. Almost everything you think can go wrong very likely will, along with a whole lotta things you never even thought of. But if you truly want to get er done, that is the single most important factor in getting er done. Those who don't go home devastated.