Today for the first time my afternoon walk took me over the same hill that I had crossed when I got the racing heart episode ten days ago. I was slightly nervous, or at least cautious, checking my pulse rather often, but nothing like that happened this time. I completed the whole circuit.

However, there is another phenomenon now. I have noticed it the last two days in particular: After about one hour’s brisk walking, my legs start to feel heavy. This is shorter than I habitually walk (around 20 minutes shorter) so the last leg of the trip, as it were, is somewhat unpleasant. But I don’t write this to whine. Rather, it kindled my scientific curiosity. Again.

More exactly, each trip has three phases now. For the first 35 minutes, the pulse is ridiculously low.  We’re talking from 110 down to less than 100 with brisk walking. Then for the next 25 minutes the pulse is typically around 120 with the same workload. And then after one hour, the legs start to feel heavy. (They always felt a bit stiff toward the end of a long walk, but not heavy, as far as I can remember.) Because I automatically slow down, the pulse also goes down a little. If I force myself to keep up the speed, it goes up slightly, but not much. So it seems to be something local to the muscles.

Why now? I don’t think the heart, even at 190 beats per minute, has the power to cause lasting changes in other parts of the body. Rather, I suspect it has to do with something else that was measured that day: My blood sugar was down to a perfectly normal 5.2 mmol, instead of my usual 6.1. As I’ve mentioned a couple times, it stayed on 6.1 even after fasting for 12 hours, and taking a 90 minute fast walk during those hours. So it moving is a bit of a big deal.

I thought at the time that either the heart had soaked up that much blood sugar, or the lower blood sugar had triggered the change in my heart rate. By now I am pretty sure that the heart – which runs fine on both fat and sugar – could not possibly be the cause. The measurement was made later when my pulse was down to around 100, the same as when walking slowly.

I won’t know until December, but I suspect that my slightly high blood sugar has disappeared. I have lost a few pounds, although I don’t seem to be losing more now, but so far they stay off.  As you may know, the fat cells (“adipose tissue”) send out a hormone called leptin. The fuller they are, the more leptin in the blood. This is a hormone that has a number of effects around the body. It lowers your brain’s appetite (although your actual stomach muscles will continue to churn when they have nothing to do). Mice who are immune to leptin have a voracious appetite and, given free food, end up double sized. But the hormone also regulates other aspects of metabolism, and is one of several factors that influence blood sugar level. Leptin is a long-term hormone, unlike insulin and the anti-insulin glucagon, which act in a matter of seconds or minutes.

So yeah, I suspect my blood sugar levels have fallen to normal human levels. Well, when I am not eating, which these days I do constantly.  Except when walking.  Perhaps I should bring along some sugar on the next trip and see what happens?