Hypocacculus wrote:I suspect the two may not really have been closely related.
Until you stopped, your muscles were working and warm and you were in full energy output mode. Your blood vessels would have been dilated, supplying lots of oxygen and energy, your heart working hard to keep the turnover going.
Then you stopped dead and stood still for 20 minutes. Your muscles would have cooled down and started going into recovery mode, starting to deal with rebuilding damaged fibres, getting rid of accumulations of metabolites and so on. Your heart rate would have dropped, your blood vessels contracted, the oxygen supply reduced and possibly fluids would have built up in your muscles. Add to it the fact that you were probably still low on carbs at the point you moved off again (until your snack kicked in), it's not entirely surprising that your system complained - I think 20 minutes to get back up to speed is amazing really, given the physiological complexity of the situation. Many sports physiologists recommend a cool down to try and avoid some of the after effects of exercise, so perhaps if you came to a halt by gradually slowing your pace for 5 minutes or so, it might help, or try eating on the move.
Your blood sugar levels are much more stable than you might think (as long as you are healthy) and the rise and dip after eating a sugary snack is pretty transitory and your response has a psychological component, unless you are actually on the way to diabetes. At other times when people like to think they have low blood sugar, what they are really experiencing is a stress signal generated by the body telling them to eat because the total carb reserve (glycogen) is running low, not the blood sugar level per se. This prompting will become more insistent the worse the situation becomes.
Blood glucose level however, will be maintained at optimum to the bitter end because your brain can't function without it. You can tell (or more likely someone else can) if you actually have low blood sugar because you will probably behave as if you are drunk, then keel over. Having worked for some years with a diabetic and having to spoon feet him honey now and then when he went 'low', I learnt the difference between the notion and the actuality quite quickly. If he was a typical example, a spoon of glucose will start to revive a flagging diabetic within a couple of minutes, with a full recovery in about 15 (and will do the same up to a point for a flagging cyclist). This is a world away from a tedious afternoon at your desk fighting off the urge to eat the second half of that Twix and blaming a dip in your blood sugar when you do. It takes about 2 hours hard exercise to deplete a full glycogen store, but longer if you are working less hard because you will be burning fat to some extent instead.
So, if you are healthy and undertaking a 50 mile, hilly cycle ride, glucose is the thing to pick you up quickly, assuming you've been drinking enough and replacing lost salt. Other sugars are less quick. Fructose is not efficient for muscles as very little escapes the liver and it has to go through metabolic gymnastics to be converted to glucose before it can be released. Sucrose is 50% fructose and glucose. A sugary snack bar or a banana or a glucose tablet or some dates (my favourite) etc will do the job quite nicely. We all develop personal preferences.
Complex carbs take much longer to digest and kick in later so will keep you going without further eating being required. They work by breaking down, releasing, either directly or indirectly .... glucose. Eating a mixed meal will also help to slow down digestion to drip feed into your system; alternatively, you could just eat a few grams of glucose every 15 minutes. For normal cycling, it doesn't really matter too much what you eat, as long as there is some glucose involved somewhere, either in the form of neat glucose, or a glucose containing disaccharide (eg sucrose), or starch which is just a string of glucose molecules. Your body isn't actually that fussy unless you are at the extreme end of sporting endeavor where different eating regimes may make a difference. Anything else you eat is just tweaking the rate at which glucose hits your system, the desired rate being rather dependent on the rate the glucose is leaving your system - only you will know when you've got it right. Of course the sponsors will be encouraging their victims to down some weird gel or potion so they can flog it to the masses. Wannabe sporting heros seem to career from one nutrient fad to the next. But ultimately, the energy for those few hours during a ride comes down to glucose. So find it in a form you personally like, preferably with a smattering of salt, and a glug of water because we all know electrolyte balance matters too.
Sorry if I've gone on too much. In case you wonder where I'm coming from, I have a biology degree, specialising in physiology and have maintained an active interest in such things since doing a triathlon a couple of years ago.
Just found this via a link from another thread.
Many thanks.