It’s been my experience that advocates of CKD’s recommend taking in some carbs before wokring out … sometimes in the form of glucose polymers (i.e., smarties). The carbs taken in is intended only to fuel the workout. Granted these are strength-training athletes. I fail to see how a no-carb or even low-carb diet would be anywhere near optimal for an endurance athlete.
I have rarely, if ever seen a trainer advise folks to do exercise with great intensity or duration without carbs.
Supposedly, Danny Chew (of RAAM “fame”) once did a century ride without any food or drink (“nothing passed my lips”). Sick puppy.
I’m certainly not disagreeing that lack of glycogen cuts ones performance. As posted in another reply some studies suggest that fat oxidation alone can only support exercise up to 50%VO2 max, which is very low intensity.
Also without doubt continued higher intensity activity after glycogen depletion will lead to the nasty symptoms you mention below. However aren’t those symptoms due to the fact that continued “higher” intensity activity is taking place, activity that demands glycogen and is taking it away from organs that can only use glycogen, namely the brain?
My question doesn’t lie with the idea that glycogen is necessary for certain level of activity, as undoubtedly it is, however is it necessary for lower level activity and or for the oxidation of fat at all?
For instance someone exercising at low level of VO2max after your series of exercises below. Would they suffer any ill effect? I.E. Excercise for 3 hours do 1 min repeats, no carbs then just walking for 4 hours. Would they still suffer the dizziness etc?
Again I really don’t know and would like to look into it further. Any links, books, articles, studies etc would be appreciated.
~Matt
BTW I did do some searching on anaplerosis and didn’t really find anything I could wrap my feeble mind around to answer the question of whether or not glucose was necessary for fat oxidation.
Here is a link to the article on Bonk training that was posted Bicycling Magazine in September, 2002: http://www.wtcycling.com/BonkTraining.html
HOW TO BONK TRAIN
The key feature of the technique was to limit workout/training duration time to 60-90 minutes maximum and the article even has a disclaimor from Liz Applegate, sports nutritionist at the University of California-Davis, cyclist and author of Eat Smart, Play Hard.:
*“If you ride like this longer than 90 minutes, your body starts breaking down muscle and protein in organs, then you’re not just losing fat, you’re weakening your body.” *
Seems to me that most of us who do things like a spinning class, short run, weight training, swim workout or combination before work in the morning are using bonk training to some extent. Afterall, I am sure I am not alone when I say I am not going to get up an hour earlier on Monday morning just so I can eat breakfast before before heading out the door for a high intensity spin class!
Michael
Another urban legend… That energy sources drawn upon by working muscles are somehow based on the availability of that particular fuel or energy source, not on relative intensity.
Lesson: If you want to improve your ‘fat burning’, strive to raise VO2max and riding/running economy so your relative intensity at any given sub max workload is less. The lower your intensity level as a percentage of your maximum capabilities, the more glycogen you’ll save.
“As for the ability to sustain low intensity exercise despite severe carbohydrate restriction/depletion, I can tell you from first-hand experience that it is quite possible to become markedly hypoglycemic at just 40% of VO2max when following a protocol such as I described.”
My only “bonking” experience was a bit different. I found that I simply couldn’t go fast. It was during a long ride that ended up being longer and a bit more intense than expected and I simply didn’t bring enough “goodies”. Seemed no matter how hard I pushed I simply wouldn’t go anywhere. The mind was willing the body would have no part in it. I do remember being quite lightheaded though not any real headaches or “hallucinations”
Once I accepted the idea that I was shot and went at a really slow pace I could keep going. Average speed went from a comfortable 17-18 mph to fairly painful 9-11 mph.
Could very well be that I hadn’t truly “bonked” either and was simply suffering from some other level of fatigue/dehydration. It was a rather hilly, for me, 65 mile ride. I only went out with two bottles of gatorade roughly 250 cal total and a bottle of water. I had also not eaten breakfast nor anything since about 7 or so the night before. Total ride time was over 4 hours. A good portion taken up by the hellish last 10-15 miles.
“Practically any biochemistry textbook will cover the metabolic pathways of relevance here, whereas any decent undergraduate physiology textbook should discuss these in the context of exercise.”
I’ll see what I can find, thanks for the info.
~Matt