Fat burning, carb burning, false hypo?

As usual, covering a wide spread of territory ;-)

My exercise of choice is bike riding.
I am trying to work up to a regular 50k route which takes me about 2.5 hours.
One day my average speed will start to rise and the overall time come down!

My take on fat burning is that when you are breathing deeply but not gasping, you are in the fat burning (aerobic) zone.
When you are gasping you are in the full on carb burning (anaerobic) zone.

My ride seems to fit interval training nicely - the terrain is mainly flat, but every few miles there is a little valley with steep sides due to erosion by streams.

So flat with minor gradients, then a steep downhill followed by a steep uphill.
On the flat I cycle at a sustainable rate where I am breathing deeply but not gasping (although I plan to start pushing myself on a shorter ride to maintain higher intensity in the hope of increasing fitness and not just stamina).
Now the hills are fairly short, but they are pretty steep.
I have managed to stay out of the 'granny' (i.e. lowest rear gear and lowest front gear) but I have come close on hills near the end of the ride.
You have to push to keep moving, so at the top I tend to be gasping and my breathing then moderates on the flat.
I stop occasionally to hydrate - haven't mastered drinking and riding at the same time :-(

So, as far as I can see, fat burning in the main but some serious carb burnings on the up hills.
A pretty good all round training regime.

However I had a bit of a wobble at the end of my last 50k ride.
Off the bike, still breathing deeply to clear the oxygen debt I had built up, but O.K.
Tested my BG as quickly as possible - 4.9 which is in the 'normal' range.
[My fasting BG at the moment is running around 6-6.5]
I then suddenly felt all light headed and wobbly and had to sit down suddenly.

Now I am wondering if this was a false hypo - although I often finish a cycle ride with my BG below 5 with no adverse reaction.
I have even done a 30k ride in the morning fasted and not had any hypo symptoms.

As far as I can tell I was hydrated, had adequate glucose in my blood stream, but had exercised to the limits of my stamina (a bit left in the tank but it would have been a real push to do another 5-10k).
So why the wobble?
I thought the wobbles (or the wall/bonking) were due to people who were reliant on carbs for most of their energy running out of carbs and not being able to utilise mainly fats.
I seemed to have a few carbs left and I think I am reasonably adjusted to fat burning as I eat low carb and mainly protein and fat.
Before the ride I had eggs scrambled in butter and coffee with a little skimmed milk.

So puzzled, and also wondering what I should do to counter this.

Does this mean I should plan in some carbs before and during the ride?
Plan in some protein/fats during the ride?

Or just http://www.velominati.com/the-rules/ #5?

Cheers

LGC

A bit of further testing but still puzzled.

I did the same ride five days later but had a fairly large protein breakfast and included malt loaf and butter as snacks during the ride.
Had a rest and walk about when eating my mid-ride snack.
I seemed a bit perkier in the mid part of the ride, but much the same energy levels by the end.
BG after ride 7.0.

Did the same ride again two days later but with no pre-ride feed or in-ride snacks.
No rest along the way apart from two brief stops to take on water.
Energy levels again about the same at the end of the ride (i.e. not a lot) and BG tested at 4.9 (same as the previous "wobble" ride).
No wobbles this time, though.

So the wobble seems to be an isolated incident not tied to eating carbs, BG levels, or hydration.

I still don't know if I am keto adapted, especially because "The Art and Science of Low Carbohydrate Performance" by Jeff Volek and Stephen Phinney suggests that any day when you take on more than minimum carbs reverses any keto adaptation.
So the malt loaf may well have scuppered any keto adaptation that I had.

Anyway I think I have found that eating carbs on a 2.5 hour 50k bike ride doesn't make much difference to my performance during the ride but does change my BG post ride (no sh*t Sherlock).

Now considering if I should carry a few glucose tabs just in case I fell 'wobbly' during a ride to see if they make any difference.
However if I can do the ride after not very much food during the day and still manage O.K. then there is probably no need.

Cheers

LGC

@phoenix (wonder if this works) - not sure why you are keeping clear.

In fact the last couple of k are flat so there is no sprinting involved; however I have reached the stage of dogged determination by then.

Further reading suggests that the "wall" is mainly caused by serotonin build up and not by complete lack of blood and tissue glucose so I may have just generated a bit too much serotonin on that particular ride.

Further testing scheduled for today.

Edit:
Phew, what a scorcher.
Should have been a two bottle ride, as I was a bit dehydrated by the end.
A slower ride, but I had to take a break for a while to cool down in the shade.
Interestingly my BG tested at 4.9 which means the three rides without carbs ALL ended at exactly the same BG.
Looks like this is my current floor for BG.

Just to be clear, I do cycle up hills in a low gear with my legs spinning - my aim is never to go into the very bottom gear - i.e smallest of the 3 front cogs and largest of the back 8 cogs.
I try and maintain a good cadence throughout the ride and only 'mash' on down slopes with a following wind to give my legs a change of pace - I find that 2.5 hours of spinning the same cadence can make the backs of my thighs hurt quite a lot but a change in cadence seems to help with this.

I tend to do steep hills in 1/4 and go down to 1/3 if I am feeling a bit weary.
I have once gone down to 1/2 but so far have never gone down to 1/1 which is the true 'granny'.
I am now looking to see if I can find out what gradient the slopes are - people are quoting 6% or whatever but there are no signs on the back roads.

I am a reasonably experienced cyclist - I cycled a lot as a kid and restarted around 1995 with a 9.6 mile each way commute to work.
I also did the London to Brighton.
I just haven't been cycling much in the last few years so the major task is to rebuild my cycling fitness.

Latest ride I cut back to 35k because it was very windy, and getting late.
I cycled at a slightly faster average speed.
Immediately post ride my BG was 6.0.
This suggests to me that it is the last 10k or so which are really pushing down my BG - when I am hitting the limits of my stamina.
So it could be a combination of false hypo and dehydration.
I don't believe it is anything to do with hyperventilation (of course I could be wrong) because I am breathing deeply and steadily when riding and immediately post ride, not very rapidly and shallowly.

Anyway, I have only had one 'wobble' so far so it could end up being just 'one of those things'.

Cheers

LGC