Is a double on a 14 mile long run day a stupid idea

"If you're running twice a day, you're wasting at least one run." Not sure who said it originally, some famous runner from a bygone era.

Right & that's kind of the point -- OP isn't there yet. One week missing an easy 4-5 miles isn't going to break them versus jumping up to a double on their current long run/fitness. I would try to double on an easy day or skip it.

Whether this makes sense or not depends on what you're trying to accomplish by doing the double workout. It also depends on what regular mileage your body can tolerate.

High mileage runners do doubles often. Lower mileage runners generally don't. But you haven't given us much information about your training history.

Based on the sparse info you've given us, my answer is, if you can do it without getting injured, then it's fine. But if you're a low mileage runner, it's probably better to spread it out for recovery and injury prevention.

I've been running for 22 years, but sure, I'm a novice. I only said "dumb idea" because that's what the OP asked, if it was a "stupid idea." Any answer will be an opinion and this is mine.

I usually like your posts but this one is dumb as hell.

I had my best season running super high mileage doing 13-15 in the AM and 5-6 in the PM most days.

Not saying it's dumb for *you* because it sounds like you did this on a regular basis, "most days." The OP doesn't provide much info on his/her training other than specifying that this is his/her long run, which to me indicates they do not run ~100+ mpw.

Lydiard once said everyone is a novice until they've run under 2:45 for the marathon.

Emphasis on the "bygone". Now that we have nearly unlimited access to better recovery activities, foods, information, shoes, etc. running twice a day is common and even leeching into the high school training philosophy depending on the athlete and program (unsure how I feel about this)

DUMB

I know Schwartz recommends doing a double after LR's. It's because it flushes your legs and removes soreness/fatigue. However, considering your running 14mi's, 6 seems a bit too much for a double. I'd recommend a 16mi LR and 4 mi double shakeout instead or even 17 -> 3

When I was training for marathons and running between 110-130 miles a week, a 14/5 day was normal, even on days where I was working out. If you feel fine, just take it easy and treat it as a shake out. You'll be surprised how good you feel after you warm up.

I'd say go for it. I run 110-120 miles a week and every now and again I'll throw in a 4-6 miles easy shakeout double on long run day. As long as I keep it extra easy I always feel fantastic afterward and it has no impact on the rest of my training

It's one run you're missing; the risk isn't worth the reward.

As others have said, running a double on a long run day isn't necessarily a bad thing.

However, when you're not running a lot of mileage (I'm assuming), adding an additional 8kms in the afternoon - after what is quite possibly your most physiologically taxing run of the week - is a little bit silly.

The old adage "don't try to make up for lost training" applies here. Your week is scheduled the way it is, so that it allows intermittent recovery. Clustering lots of runs together without gradually building that into your training can easily put you over the edge.

If your regular long run is 14 miles, maybe just do 15 miles this week instead, and leave it at that.

Your goal is <3:50, no offense but "doubles" shouldn't even be in your vocabulary at this point.

Just skip the 5-mile run. Skipping one 5-mile run is for all intents and purposes going to have zero effect on your June marathon time. The injury risk will not be zero, however.

"I run twice a day, every day, except on Christmas."
- Haile Gebrselassie