I’m not sure I’d say they’re out of sync necessarily. However, a lag is only one part of the problem. My Dexcom, which was also true for the Libre, often overshoots on a climb. I know that’s not what you’re describing at all, but I’m just trying to demonstrate another pattern. The lag, obviously, results in a less extreme sensor value than my actual BG, but the overshooting does the opposite and appears to be a more extreme value than my BG.
I just can’t much rely on a CGM during exercise. That’s the conclusion I’ve come to. I understand it is really meant for trend, and that’s fine during other times of the day, but because I can get a little BG bounce going on during exercise, those numbers just can be too deceiving. I become afraid I’m still crashing when, in fact, I’ve already turned. Or I think I’m good when I’m headed down fast. For all of these reasons, and thanks to Eric’s encouragement (and gadgets!), I’m testing all throughout the run. I’ve stopped looking at my Dexcom or responding to any alerts at all because I’m always a few steps ahead of it. If it’s letting me know I’m headed down, I’ve already spotted it and taken action. I, personally, just can’t stay on top of it with the CGM because I’m basing my decisions on flawed numbers.
This isn’t a pitch for going CGMless during your run. I was just trying to confirm that there’s lots my CGM is showing during my runs that just isn’t reliable. Which, I guess, might make this a pitch for doing a Fingerstick or two while you’re out.
Today my dexcom took note of my climbing BG as I got on the treadmill. I was starting at a BG of 134, Dex 123 (or so). My Dexcom over the next 10-15 minutes showed a steady climb up to a 179 with arrow up. My actual BG at that time was a 124. Next value was a 179 while my actual BG had dropped already to an 89. I’m not mad at my Dexcom, but I’m learning that I stand a better chance when using meter readings.
I had one other thought…
Oh! About not feeling your lows. This also might not pertain, but today I dropped to a 50 during my run, and I was wobbly as all get out. I was spacewalking, uncoordinated, and just feeling like I needed to be done. I felt that 50 way more than the 40-something I had in the middle of my run last week. Even as I got back to ~60, I was just wrecked. Last week I think I ran 6 or 7 miles in the 55-65 range. I’m not sure, but I think when I drop fast at all during the run, I feel the low more than when I coast low. Today was a low 50. The other day was a fine 50. Today I had insulin on board, and the other day I didn’t.
And it could all not apply to you in the least. These are just the things on my mind these days.