Intense cardio = sleepy?

[Cassiel]

I've been doing some pretty intense cardio on the eliptical lately just because I can - I'm impressed by how high I can get my heart rate without feeling like I'm doing much. In fact, according to two different heart rate monitors (I was suspicious so I tested this - it seemed a little extreme) I can easily get my HR up to 180. I'm 28, so that's a pretty high percentage of maximum. Not that I would mind pushing up my VO2max. It just amazes me how long I can stay in the high 160's to 180 without wearing out. I did 7.25 miles today with an average HR of 172.

What this results in, however, that I have never experienced post-workout before is a high level of sleepiness. I don't mean fatigue - I always get a pleasant weariness whether I've run, swum or cycled. I mean actual sleepiness. I was sitting in my car because I was early to an engagement this afternoon and I fell asleep (thankfully I woke up in time).

Any ideas what this is about? Am I suffering hypoxia or something? Is the high cardio intensity drawing blood away from my brain and killing brain cells? I don't feel any dumber...not yet anyway... :dunce:

[beepbeeplove]

I used to always feel sleepy after intense cardio :) I don't think it would be killing brain cells, high intensity cardio improves neuron function/lifespan.
I think with heart rates it varies from person to person what is intense. What I would call moderate effort gets my heart rate up to about 185, but it doesn't feel difficult. You must have a heart that is strong enough to beat quickly, that sounds like a good thing :)

[elektra513]

IMO you're not getting enough calories to support your exercise immediately after. Maybe you should eat something substantial afterwards?

[desertowl]

I always get an immediate boost of energy after cardio.

[lobsteriffic]

Immediately after intense cardio I get that exercise boost. But a few hours later I get sleepy too. I just chalk it up to being exhausted from a really good workout. :)

That being said, make sure you are getting plenty of sleep at night and eating properly to support that level of activity.

[Jalden]

If it's not that your just plain wore out it could be low blood sugar. You burned it all up :).

[Cassiel]

See, the funny thing is that all those things - blood sugar, caloric intake, etc - I shoudl have a handle on by now. I'm an endurance runner who has done a number of marathons and a lot of smaller races. I just don't remembering being so sleepy after doing an intense workout before. I like doing endurance sports because I'm better at endurance than speed, so I tend not to go for high intensity, but rather long duration. This high intensity business is relatively new.

[Aynsl156]

I always chalk it up to electrolyte depletion, and make sure to eat something high in magnesium and potassium after a long run.

[Masja]

I get this way too...then again I don't work out intensely, but at home when I'm working out on my stationary bike you will find me yawning throughout, even though I keep a pretty good pace. Also afterwards, I'm exhausted and soooo sleepy. The only thing I found helps is to drink a ton of water and try to go a little longer, as I find I'm most tired if I do less than 20 minutes or so.