For many years, I've noticed that about a half hour after finishing moderately intense activity lasting more than 5 hrs (e.g. long bike ride, back country skiing, etc), I go out like a light. Nothing keeps me awake -- stimulants, self induced pain, freezing, whatever -- the sleepiness hits me like a wall so I stop wherever I am. After just 10 minutes of being out cold, I wake up feeling great/energized, the risk of going back to sleep drops to zero, and I'm good for hours.

I'm not fishing for medical advice as nothing is wrong, but I'm wondering what causes this? It can't be fatigue because if I ride/ski literally all day, I never get sleepy until about 1/2 hr after I stop. On the other hand, it is related to the amount of time I'm out since I never see this effect if I'm only out a couple hours. What gives?

Maybe you should seek medical advice. I was under the impression that most people find it difficult to sleep immediately after vigorous exercise - I know I do.

Cover your eyes with a blank or towel blocking all light. That helps a lot. Drinking too much water before sleep keeps me awake. Try lowering the room temperature.

are you serious?

My reply would be age creeping up on you. Same type of thing happens to me after really intense exercise or efforts/hard work.

I don't have any answer, but it sounds awesome. That would be great for longer randonnees.

Immediately after, I also do. Wait 1/2 hr and I'm out. But only for a short time.

I actually did ask my doc some questions a few years ago. She literally laughed at me -- diagnosis was that I thought I was 25.

Come to think about it, having your bladder feel like it's about to explode is surprisingly effective and works better than other discomfort inducing methods.

I think it's just another manifestation of your Super Fredliness.

10 minutes of deep sleep and Wham! good for hours? Thank your lucky stars.

Tryptophan, among other things.

The same thing happens to me, but I can fight it. The problem is I put my kit in the wash and hop in the shower immediately after coming through the door. So I go from dirty and uncomfortable to clean and comfy rather quickly. I usually can't help but crawl into bed right after this process and the end result is that I can pass out pretty quickly. I usually only sleep for 10-15 minutes, just like you, before I snap out of it and go out for a nice dinner and beer.

I think that's just how it goes when you punish your body for 5 hours.

By definition, 5 hrs of exercise is generally not 'vigorous'.

What's your definition then? Most people I know are too lazy to get off their fat asses to do anything and 5 minutes of physical activity would be the end of them. If we're talking about intense efforts on a bicycle, 5 hours is more than enough to fully drain the body from head to toe. I consider that "vigorous."

Something with high intensity in it. Like playing an hour of ice hockey which is basically 20-30 45 Second sprints. Or doing a set of zone 5 intervals on the bike. A 5 hr ride is done at low to moderate intensity. Your HR doesn't generally get anywhere close to it's maximum. After an ice hockey game or a crit race I'm 'wired' and wouldn't be able to sleep. Perhaps it has something to do with adrenaline or some other hormone. I'm not wired up after a long zone 2 endurance ride, just pleasantly relaxed.

A lot of people plan their effort so they use up their stuff in the time available. There's no need to lollygag just because you're out for awhile, nor are you prohibited from sprinting -- even if I'm out all day, max HR will top 170. Besides, if you're spending the vast majority of the time climbing mountains on a bicycle or skis, it's not like you're going to be taking it that easy.

That happens to me once in a while. I don't fall asleep, but, it's easy if I try.
I once had a coffee in the morning and none in the afternoon. So I had a caffeen crash at that time of day. Which made it worse.
If you have one coffee in the morning you need to have another later in the day if you're doing a long ride.
Or stop drinking coffee totally. A friend of mine had the exact same problem when I was training her for a century ride. She had a huge cup of coffee,in the morning, then nothing. Fixed now.

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I actually did ask my doc some questions a few years ago. She literally laughed at me -- diagnosis was that I thought I was 25.

She nailed it.

I avoid caffeine like the plague. The lone exception is when I want help staying alert behind the wheel. But if I'm crashing, no dose can save me -- even a couple cans of Red Bull and chewing a serrano has surprisingly little effect.

For a little boost when I plan to be out for awhile, my go to for years has been to toss down a couple bottles of Ensure Plus. Easy on the stomach, it gives good energy, and there's no crash. It's also not bad for recovery.

You're not trying hard enough.

Fine, but if you use up all your 'stuff' in a 5 hr ride you'll be drained not wired. And if you use a power meter you can pick any metric (NP, IF) that measures intensity and it will be significantly lower for a 5 hr ride vs a shorter high intensity ride. I equate vigorous with high intensity and that's not possible for 5 hrs.

Correct. But that logic can be extended to just about any time period exceeding 30 seconds.

While you can certainly push yourself to the point that you can barely stand after a shorter ride or an interval set, you'll never feel sleepy. But this is a common situation for me after longer rides. That I wake up feeling great after just 10 minutes in most cases tells me that it has more to do with what's going on chemically in my body than fatigue and that whatever is going on is not just a function of effort since I push myself harder on shorter rides. Wrapping my mind around what is going on was the motivation for the original question.

The same thing happens to me, and I don't fight it at all. I tend to believe that if I exercise for hours and I'm tired afterwards... pretty natural. That little 10-15 minute nap does wonders. It's a good thing.

Try throwing yourself in a lake, that should do the trick.

I think you're making it more complex than it is. Long rides are fatiguing and it's perfectly normal to feel tired.