coffeecherrypie

So if I forget to bring an energy bar or whatever, somewhere between 2 and 3 hours into a ride with a lot of climbing I start to get tunnel vision. Like, I literally start to lose my peripheral vision and I have to really concentrate in order to make sure that I'm processing what I can see correctly. My legs feel fine, my energy feels fine, I'm not out of breath, I don't feel exhausted, I feel like I could keep going for a while--except I almost can't see. I assume this is like a blood sugar issue? Or liver bad at releasing glycogen? Is this common? I got into cycling late but I would guess that this wouldn't have happened when I was younger (I'm 37).

Edit: and then after the ride, when this happens, I feel like I need to go to sleep--but for "head" reasons not for "body" reasons, if that makes sense.

Bassmanbob

It sounds like you were hypoglycemic (low blood sugar) and you were about to pass out. I almost passed out (not cycling) but that’s how it felt. It was as if a black curtain was closing from both sides.

If you sometimes forget to take an energy bar, I would consider always having some kind of electrolyte powder in at least one of your water bottles. Also, go get a physical with your doctor if you’ve not had one recently. Make sure your heart is ok and no diabetes is developing.

nomadmax 

Given your lack of perceived exertion during the hypoxic vision change (due to the brain not getting enough oxygenated blood); I'd go get a full physical and tell the doctor. Tunnel vision during massive efforts should be accompanied with a great deal of perceived exertion. I'm not a doctor but there are serious vascular conditions (in the neck) than can starve the brain for oxygen when the rest of the body is in an aerobic state (operating with enough oxygen for the task).

Seriously, get that checked asap.

WhyFi

No, and it's not condition where you look to random internets people for consultation - go see a doctor.

eduskator

Frankly, I will go see my MD if this ever happens to me. This seems serious enough to seek professional advice. Unless there is a physician on this forum, you'll get tons of non-relevant answers.

I ride fasted almost all the time, but my usual rides are 2h max. Anything longer than that, I take a dried fruit bar and I carry a protein bar in case.

10 Wheels

Have You had a Brain Injury?

I had a Mini Blood Clot caused from medication.
It only showed up on an MRI

WhyFi

There are a handful and I would expect that all would advise to him to see a doctor.

Steamer

Not normal. See a doctor.

coffeecherrypie

Sorry, I don't think I was clear. There's plenty of exertion happening, I was just trying to get across that other than the vision issue it doesn't feel like my body has totally run out of energy.

Today I did a harder ride than yesterday, brought an energy bar, and was fine -- compared to yesterday when I didn't bring an energy bar and it happened.

I suppose I will heed everyone's advice and see a doc sometime reasonably soon. I'm not *super* concerned since an energy bar seems to avert this from happening, but may as well cover all bases. Thx all.

coffeecherrypie

Yeah thanks. I usually stick a Nuun in for the caffeine but that has no calories. I will probably just make sure I never ride w/o some form of extra calories in the future.

Sy Reene

Also maybe not a bad idea to make 1 of your 2 bottles with an energy drink.. my recipe:
1/2 tab Nuun
1/2 strength gatorade powder (about 1/4 scoop per bottle)
1.5 scoops maltodextrin powder

Koyote

OP: Are you stating that, on a 2-3 hour ride with lots of climbing, you just eat a single energy bar? I wouldn't think that is enough. And if you forget the energy bar, yeah, you're gonna suffer.

WhyFi

Hard 2-3 hour rides, without additional calories, aren't an issue if you're conditioned for it. More to the point, if a mid-ride snack prevents tunnel vision, I have a hard time believing that there isn't some other underlying condition.

WhyFi

I'm sure that datlas and MoAlpha will appreciate being tagged in this thread.

Koyote

I don't know whether the OP has a medical condition, so we agree on that. At 37, he should have an annual physical with a doctor.

I agree that a fit rider can indeed do a hard 2-3 hour ride without additional calories...But some additional carbs will enhance performance. (If I'm wrong, I sure would like to see the sources.)

WhyFi

What are your sources?

You should have 2000+ calories in glycogen reserve.

Koyote

My sources are pretty much every training book and site I've ever read. A few (from a quick google search) are listed below - I haven't read them carefully, just scanned them, and they all seem to confirm the advice of around 60 calories per hour (with caveats) beginning 60-90 mins into a ride. But: I do wonder just how much of the "conventional wisdom" is driven by companies that make energy bars and drinks, so am interested in reading your source(s). I don't know enough about on-bike nutrition, so am sincerely interested.

https://trainright.com/what-to-eat-a...e%20necessary.

Coach Hughes: Nutrition for Cycling Endurance

https://www.theglobeandmail.com/life...030%20minutes.

oleg232000

I personally do 3 hour rides multiple times a week with a good amount of climbing and exertion and I never take extra fuel, besides a water bottle, and even then sometimes I go the whole ride without taking a sip. I do fuel up before the ride though, but never during. I've went 5 hours without a single calorie and felt fine and could keep going. But to the OP, were you at any high elevation by any chance? And did you consume caffeine or an abnormally large amount of caffeine prior to the ride?

WhyFi

So look up information on glycogen stores and take a look at your burn rate (if you have a power meter) and get a feel for it on your own rides. Eating on a two hour ride is undoubtedly no benefit for me, given adequate stores at the outset, and at three hours I'm still very much in the "is it more trouble than it's worth?" tipping point.

datlas 

No thanks. The tunnel vision symptom suggests possibly hypotension (drop in BP to the brain) but the history is more consistent with hypoglycemia.

The OP should see a doctor in person just to be safe.

coffeecherrypie

Negative to high elevation. I have one espresso in the morning and head out on the ride. During the ride I have a Nuun in the water bottle which I guess would be the equivalent of another coffee.

coffeecherrypie

Just reading about glycogen. Seems like one should be able to store roughly 2000 calories worth. I guess *if* I'm on the low end of that and *if* I'm burning ~750 calories per hour (tho that seems high?) then I could just be running out at say 2.5 hours in. So maybe I'm just "bonking" after all and it's manifesting as tunnel vision. I definitely don't do a good job eating carbs before a ride, I usually eat yogurt in the morning before heading out. Nonetheless, I will talk to a doctor about it at some point this winter.

With respect to hypotension, I don't have any other symptoms like problems when standing up quickly .

genejockey 

Define "lots of climbing"

Up until last month, my Sunday rides were routinely 2 1/2- 3 1/2 hours with 2-3000 feet of climbing (per Strava), and it wasn't till I started stretching them to 4+ hours that I felt any need for food on the ride. In fact, I had the same Clif Bar in my jersey pocket for a couple months.

Koyote

I'm glad you know what works for you, but don't confuse your personal impressions with evidence.

Here is an article from the Cleveland Clinic which references the American College of Sports Medicine. The takeaway line is "Cyclists riding for longer than 60 minutes need to start to fuel after one hour."

Here is a peer-reviewed journal article on the subject, which includes the observation that "In practical terms, 2 hours or more of even moderate physical activity (eg, 65% VO2max) is sufficient to markedly lower muscle glycogen stores."

Here is an article by Selene Yeager which seems well-researched. Again, the recommendation is to start eating carbs even on moderate-length rides.

etc.

Bear in mind that your body needs glycogen for more than just working your legs while riding. So, even though your body can store a bunch, that doesn't make it all available for exercise.

When I was starting out, and knew very little, I would routinely go on 50-60 mile rides, and longer, with just a couple water bottles and a Powerbar in my pocket. I could do it. But that didn't mean it was optimal.

Gary in NJ

Not normal. The only time I've ever experienced true tunnel vision was while under a 6+g load for 10-15 seconds. As soon as the g's dropped my vision returned to normal. This happened over 30 years ago and it was rather disturbing to me.

Go see a doctor before you pass out on the road and get injured or killed.