Discussion: intervals cause blackouts?

So, yesterday I went interval training with the Warwick Uni O-club (I'm visiting for a week). First time doing intervals for a month. Training has been sub-optimal (to say the least) for the last few months, but I'm still reasonably fit...

Warm-up was maybe ten-fifteen minutes of jogging with a few strides thrown in.

1km intervals... first one I went out pretty fast but it didn't seem excessive - turned out to be 3mins - had no trouble running it.
2nd I ran with gg, maybe 2 seconds faster than before, had a little trouble!
3rd I had to slow down, maybe 25 seconds slower.
4th was similar
after the fourth i started getting slight pins and needles sensation in lower arm, head etc. decided not to run the fifth and final...
so some very slow jogging followed.

then started gentle jogging back to accommodation, felt pretty awful. dropped to a walk. was a bit cold, started having trouble breathing. then had trouble thinking and seeing... things were getting blurry
made it to a bus shelter and sat down... more of the same (not much vision left). got on a (warm) bus, put my head between my knees and waited for my system to start functioning "properly" again... by which time i realised the bus wasn't going the way i wanted and had left campus in the wrong direction. had a nice long walk home in tshirt and shorts.

so... anybody out there with a physiological explanation? is this a "normal" occurence? should i be going to the doctor?

should i be going to the doctor?

Maybe. None of us can diagnose based on a brief text description. If it doesn't happen again, then you may not need to worry about it. If it does, then it could be any of a number of things, so...

I will offer an anecdote about a friend (Nancy's nephew), who is a very good high school runner (and occasional ski-orienteer). He started having problems this fall where he would have problems similar to yours when he finished races. Sounded good to me, he was winning races by giving it his all. They were worried and took him to the doctor, who put him on a treadmill and gave him a stress test. Doc was very impressed by how fast and hard the kid could run, and when he finally couldn't take it and had to stop, sure enough, here come the symptoms. Blood pressure dropped through the floor (well, almost, I think they said it was 35/0 or something preposterous like that), and the diagnosis was dehydration, so now the whole family keeps pestering him to drink a lot of Gatorade all the time. Which is fine... although apparently he also had the symptoms once while in church. Stay tuned for more info when the spring track season starts.

Dehydration during a stress test??? Seems pretty unlikely. There's a pretty common condition that people get at end of races which causes loss of blood pressure and faintness/collapse called postural hypotension..(and is often confused with dehydration). Doesn't explain why your mate gets it in Church though.

Here's a couple of links

http://www.time-to-run.com/theabc/collapse.htm

http://www.rice.edu/~jenky/sports/collapse.html

should i be going to the doctor?

Definatelly.

I'd be concerned about pins and needles sensation described. Guy from my son's speed skating club had similar symptoms during speed skating practice couple years ago, was able to go to hospital on his own however he was hospitalized right after. I believe he had TIA but I am not an expert. What I do remember from his recount of events that it started out with strange sensation in his arm. Some of other symptoms described match symptoms of TIA if you check the link below.

http://www.nlm.nih.gov/medlineplus/ency/article/00...

I'm wondering, did you do 1 Km in 3 minutes? That is under 5 minutes per mile pace; and this was easy? The pins and needles sensation comes from lack of oxygen, usally in a periphery like the hands. Blood is pumping to the legs and internal organs. You overdid it. Next time run the first one easy(?) and increase speed in later intervals if you have not been doing them regularly. Maybe 1/4 mile intervals would be better.

I'd probably see a doctor. I'd rather waste his/her time and find out I was fine than drop dead during intervals - although that is a good way to get out of doing them.

I might also approach running a sub 3 minute kilometer the same way I plan to approach a hole in one in golf. Just drop the clubs and walk back to the clubhouse for a beer and never, ever play again.

As J-J said, there are multiple possible causes for these symptoms. It reminds me of my collapse at the Big Muddy Rogaine 8-hour last spring, when I ran or (fast hiked uphill) pretty hard for 6 hours, then had moderate nausea along with cramping in multiple leg muscle groups, followed an hour later (after only slow walking with frequent rests) by my heart rate suddenly dropping to 36 bpm for 1 minute, during which I almost blacked out while sitting with my head down between my knees. The cause of this episode was almost certainly hyponatremia/hypokalemia ("water intoxication") from drinking too dilute an electrolyte solution while exercising in hot weather (the first I'd encountered that year, so my body wasn't acclimatized). I also may have been dehydrated (and simply low on electrolytes, too). I felt progressively better after taking several electrolyte capsules with water.

I'd see a doctor if I were you. A doctor can perform or order a few simple, standard tests to rule out (or indicate) a lot of possible problems.

How much sleep have you been getting? I sometimes get dizzy spells when I train on too little sleep. It can also happen in the latter stages of long (over 18 hour) races.

some people run 4min miles, 20% faster... well, I'm not sure they are people.

So, thanks for your comments and possible explanations (more are welcome). I don't think TIA is the cause, might get my cholesterol etc. checked out though anyway. I'd bet on the postural hypotension hypothesis. It seems consistent with feeling better after lowering the head for a while.
No links said anything about having a bit of trouble breathing, however.
I'll probably go to the doctor when I get back to France, but only if I get to waste their time more than they waste mine :)
Went running yesterday and today (not intervals!) without any noticeable after effects. Indeed, even on Tuesday evening, once I had warmed up and got food into me I felt way better than I expected, much better than say after an all out sprint race...

Nobody mentioned food... the whole week before doing intervals or a race is very important in terms of fuel. You might have just ran out of gas. Look back at what you ate that week and make sure you weren`t undernourished. IF you burned all the reserves you had in your muscles, then you had to go get is somewhere else. That`s the easiest explanation in my opinion... and easiest training mistake to make ;-)

Not to be alarmist, but difficulty breathing and thinking following exercise could also be related to your heart. Probably not, but why take a chance? Glad you're going to see a doctor, just to rule things out.

While we're throwing out hypotheses, I'll offer that it could have been a panic attack, although I don't know if these happen following exercise.

In that case, maybe it was just very bad wind.

I'm sure it's a different problem, but I have blacked out or come close after intense exercise a few times with a condition known as exercise induced anaphylaxis.

Basically I have a (not yet pinpointed) food allergy that only causes trouble in conjunction with exercise. The symptoms usually start with itching (really bad) of the hands and head, sometimes I get welts, when its bad, swelling of the face, lips and tongue, some difficulty breathing, and particularly after I stop, I have problems with blood pressure dropping (and hence passing out).

Probably something different, but if you feel like passing out, lie down and stick your feet in the air :) It helps a lot.

Forgot to add - in my case a 4 hour fast before exercise has fixed the problem. This is not ideal for an athlete and makes PE teaching problematic, so I am hoping to isolate the allergy soon. Sports drinks and carboshotz during exercise have been fine.