Quoted post said:Originally Posted by CycleFast [IMG]/img/forum/go_quote.gif[/IMG]
It might be, it depends on the exact definition of bonking.
I've experienced bonking several times before, but the symptomes has then been the classical symptoms; dizzy, hunger for food, loss of muscle control, sweating, etc. Noen of these symptomes occured on the ride in question. It was only my legs that lost power, all other bonking symptoms were not present.
I would think it's possible to have "muscle glycogen depletion" without having low bloodsugar (which is the cause of bonking)? [IMG]/img/vbsmilies/smilies/confused.gif[/IMG]
FWIW, in my wife's MS RD studies they introduced two concepts related to exercise and low glycogen/glucose conditions. In their terminology they discussed 'hitting the wall' and 'bonking' as two related but different concepts with the following definitions (my loose paraphrasing as I wasn't in those classes):
- Bonking: depletion of blood glucose and glycogen/glucose stores in the liver leading to problems feeding the brain as the brain requires sugars as it's fuel source and cannot directly use other macronutrients (though it can indirectly through ketoacidosis and catabolizing muscle protein to produce sugars but that is a relatively slow process). This is the classic tunnel vision, feelings of despair, mental bonking that many of us have experienced and it's mostly a brain related issue. You can turn this around fast by ingesting high GI carbs so eat immediately if you start to feel this coming on.
- Hitting the wall: depletion of muscle glycogen stores from your working muscles. When this happens we have no choice but to back down to lower intensity exercise that primarily burns proteins and fats. This can take a long time to bounce back from as glycogen synthesis rates are relatively slow and our muscles consume blood sugar very rapidly when working out so it's hard to ingest enough sugars to fuel both the muscles and brain. Still if this happens with or without the bonking you want to get sugars on board, just don't expect a fast recovery to full strength.
The two often happen together but not necessarily. If you've been working out a lot day to day or are on a low carb diet (not a good idea for endurance athletes) you can be partially or largely glycogen depleted before the ride even begins and run out of glycogen in the working muscles even though blood sugar levels are decent and the brain is fine. Of course continuing to workout in those conditions can rapidly lead to bonking as you burn through your blood and liver sugars an start to starve the brain. I suppose it's also possible to do the reverse during very high intensity workouts where you begin to starve the brain on acute blood glucose supplies even though the muscle glycogen is in good shape. That starts to look like diabetic issues of acute low blood sugar even if the root causes are different and your insulin levels are fine. But in either case ingesting simple sugars is a pretty good idea.
Chronic glycogen depletion is a real problem for folks working out hard, long and or frequently. Critical half hour refueling after workouts is a really good idea as your body syntesizes and stores glycogen at much faster rates immediately following exercise. In that first half hour to hour after a hard or long workout your body can convert carbs to glycogen up to twice as fast as it can after that useful refueling window closes. So get some high GI carbs along with some low fat protein on board immediately after long or hard workouts if you plan to workout again soon. You can do this with commercial recovery drinks, with something like a fruit smoothie with some added lowfat yogurt or protein powder (emphasis on the carbs but some protein has been shown to be useful as in 3:1 or 4:1 carbs to protein) or with a lot of folks favorite, low fat chocolate milk which has been shown in some studies to be as good as the commercial recovery drinks and is widely available in convenience stores and supermarkets.
If you do deeply deplete your muscle glycogen stores it can take several days to fully replenish those stores so it's best not to go there. Also muscle glycogen is not mobile between muscle groups. IOW, your arm muscles could be fine on stored glycogen even as you deplete the glycogen in your primary leg muscles while cycling, that glycogen in your arms does not help your legs as the glycogen in your arm muscles cannot move to your leg muscles where it's needed.
In terms of on the bike fueling, most folks can only ingest and process roughly 250 to 300 Calories per hour while working out. Attempts to force down more fuels usually leads to GI distress and cramping which can end your ride in a hurry. But riding hard can burn through sugars at a much faster rate. You burn roughly 360 Calories per hour at 100 watts average power, 720 at 200 watts AP and 1080 at 300 watts AP. The closer that average power is to your FTP the more those calories come from sugars and the less from fats and protein. So it's a deficit spending game, you cannot ingest enough to cover everything your burn unless you ride at a very low intensity.
You can steer things towards burning fats and preserve muscle glycogen stores by managing intensity relative to your FTP. For instance if you limit your riding to say 70% of FTP you'll burn a higher percentage of fats and preserve some glycogen and we have plenty of fats on board so that's a good thing but it means pacing back and going slower. So in addition to raising your FTP to deal with hard fast sections of riding or to TT faster or to climb a long hill faster a huge benefit of increasing FTP is the ability to ride relatively fast and hard but to do so at a reasonable fraction of your FTP so that you preserve muscle glycogen and avoid hitting the wall or bonking.
For instance if two riders of the same size and weight have FTPs of 250 and 300 watts respectively and the race pace in the group forces them to hold an AP of 200 watts then the rider with a 250 watt FTP is riding at 80% of their FTP and the 300 watt FTP rider is only riding at 67% of his FTP. The second rider is doing a much better job of preserving muscle glycogen and is much less likely to bonk or hit the wall at this pace. So in addition to freshness and recovery concerns or the ability to deal with the fast and hard sections of the race the rider with the higher FTP has extra endurance from a fueling standpoint as they can rely more on fats at the same pace. IOW, it pays to be fit in many ways.
-Dave
