WhyFi

That's why I said to research glycogen stores *and* reference your burn rate via power meter and feel it out for yourself. The likelihood that the average weekend warrior is putting down enough wattz to outstrip a full gas tank at these durations is pretty low, though. What kind of kj/hour are you seeing on your 2-3 hour rides?

...or what?

Of course it is, the question is to what kind of impact, if any. This study is chiefly concerned with pre- and post-exercise intake and to ensure adequate stores.

That's an article about someone that ate too much on the bike and how they saw improvements by drastically cutting back - kind of approaching from the opposite end of what you're arguing, no?

If you were looking to waste my time by having me read through irrelevant links - well played, but I won't be fooled again.

Erzulis Boat 

Pretty normal if exertion is very high.

In my late 20's I would get tunnel vision when my HRM would bang 240+ on climbs (normal "max" was around 210). Sometimes just a hint of shaded areas, but occasionally full blown.

If you really push it, sooner or later it will manifest itself with varying degrees.

Koyote

You seem to conflate your own experience with evidence. I just wouldn't want the OP, nor anyone else, to confuse an anecdote with actual science.

Iride01 

Do you know what your HR was at the time you were having this? I would talk to a medical professional about it. If it's more than a one time thing I'd go right now. Drops in HR while doing a fair amount of exertion can be several signs of cardiac issues and along with Hypoglycemia, Hypotension then there are plenty of possible things you ought to make certain about.

genejockey 

As we say, "The plural of 'anecdote' is not 'data'."

DangerousDanR

There are several causes of transient visual disturbances. Low blood sugar, optical migraine, brain injury or swelling,.. and probably a whole lot more.

You need someone with a team capable of determining which one of the list is the actual cause.

In the past I was a Firefighter / Medic, with a whole pile of certifications that said I knew that air goes in and out, blood goes round and round, and oxygen is good. I had a sarcastic speech prepared for people who asked me is this X; "I don't have x-ray or an MRI or a lab in my fingers, so the best I can do is take you to a place where they have all that stuff..."

Koyote

I would've written that, but we don't even have multiple anecdotes in this case.

Carbonfiberboy 

i wasn't going to comment except to say see a doctor, but that's been done plenty. I could add that I have been in severe stress situations on the bike: riding another 40 miles of hills after a complete bonk, hard 400k rides in the mountains, serious dehydration with HR 40 beats above normal, going cross-eyed from the exhaustion of the eye control muscles, going so hard the whole world went black and as they say, I saw Moses. Never tunnel vision. Never heard of that happening, either. Not good. See a doctor.

Except for no migraine, this is one of the usual symptoms of one coming on, though hallucinatory patterns are more common.

big john

I never had tunnel vision, per se, but if I spend a long time in the drops while pushing hard my vision gets a little wonky. If I sit up it clears. I've heard other cyclists mention this.
I'm 66 and I can do 3000 feet of climbing in 30 miles without needing any snacks but it's nice to have something anyway. 50-60 hilly miles and I want to eat along the way. I always have breakfast.