Still not sure about the muscles and energy thing. After I came home on Saturday, my pulse remained 10-15 beats above normal for at least a couple hours. I was also warmer than normal. According to the “muscles store energy” theory, this probably came from my leg muscles recharging, drawing energy from elsewhere in the body. But as I said, Wikipedia and a couple more pages of highly respected websites don’t believe that muscles can store energy like a battery, just a substance known as glycogen, basically very densely packed glucose (the simplest form of sugar).

If that is the case, then presumably my leg muscles were storing up glycogen by drawing glucose from the blood (where there seems to be no shortage of it, based on recent blood tests – I am not diabetic, but the blood sugar is at or just over the upper boundary of normal). There must have been rather a shortage of glycogen if the mucles had to increase the flow of blood to get enough sugar. You’d think since the heart is beating anyway, the muscles could just pick up sugar as it passed.

Yesterday it rained like a bathroom shower, and my jogging shoes soon became soaked all the way through. They are not going to last long if I use them for wading, so I returned home after only about half an hour. That put an end to my plan to check whether the energy reserves had regenerated fully.

Today I took a 1.25 hour walk. I carried my umbrella, even though I only needed it for a short while. I am not sure if carrying something had an effect, but my heart rate was somewhat higher and I burned more calories than on the first trip Saturday, although less than the second. I guess it may count that I also jogged down the other side of the hill and a few other places where my pulse started getting too low to count as training. Burned about 800 calories (kcal), which is pretty decent for that length.

However, I did not trigger a forced recharge this time. There must have been some reserves left, because my pulse almost immediately fell back to normal range. So evidently if I don’t discharge past a certain point, recharge will happen entirely in the background. That is what I thought, since I normally don’t experience any disruption of heart rate or breathing after I took up the habit of walking briskly for an hour.

Then again, according to what I learned before, the body should be burning mostly fat during so moderate exercise. OK, I guess climbing those hills might need some faster energy, but still. In theory the body should use mostly fat, and I have enough of that to walk for weeks.

I wish I had meters in my body so I can see what it is doing. It would be cool to be able to monitor my blood sugar, blood fat, remaining sugar storage and fat storage. Clearly the body does know these things, because it adjusts to them on the fly. But unless I take things to extremes, I cannot actually feel the variations. Then again, thanks to the glucose syrup tests, I seem to have achieved the ability to feel my blood sugar being higher than necessary. It is a kind of acute “fed” feeling, if that makes sense. It is different from the long-term “fed” feeling that comes from having my fat stores reasonably filled. (I am still not fat, thanks for asking, but I have more than I realistically need in peacetime.) So perhaps with the right experience, I may become able to feel other statuses in my body too. If I live that long… Just to be safe, I don’t think I will be running any marathons anytime soon!

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Edit to add: Found it! The answer from nycgirl here is loaded with useful facts about glycogen.  Evidently even a walker like me has several hundred grams of the stuff, and it is always used in the beginning of any exercise (thus the low pulse during the first quarter, I guess). With slow and steady exercise, fat is burned but together with glycogen. This is probably which happens after I am fully warmed up.  I still don’t know what the trigger threshold is that causes my pulse to rise to the next level (after an hour or so, in my case). I also don’t know where the trigger is for the forced “recharge” after exercise.  Saturday I spent 1300 calories, and did get the recharge effect. Today 800 and nothing.  So more studies are in order.