5 Insights from Training with a Continuous Glucose Monitor
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Final yr, when reporting this post on the rising pattern of stamina athletes making use of constant glucose screens (CGMs), I tried out it myself for two months. The initial post concentrated on the science (sparse even though it is) at the rear of statements that recognizing what your blood sugar is carrying out at any presented minute can enable you fuel much more properly and accomplish improved. But I figured it would be exciting to share some of my actual CGM data—so what follows are five consultant samples that illustrate some of my experiences.
To enable me interpret this knowledge, I named Kevin Sprouse, a sports medicine medical doctor in Knoxville who also serves as head of medicine for the EF Instruction-Nippo pro biking workforce. Sprouse makes use of CGMs with his Tour de France cyclists (even though not through competitors), as properly as with recreational athletes in biking and other sports.
To start, I emailed him some exercise data—which, it turns out, is completely the completely wrong technique. “It’s definitely significant to glimpse at the 24-hour period of time close to the exercise,” he discussed when we talked. “Looking at just the exercise is a miscalculation. It is myopic.” Small blood sugar through a exercise may possibly be the result of a undesirable meal the night in advance of. Higher blood sugar may possibly merely point out that you didn’t get enough rest. Devoid of individuals contextual clues, the exercise knowledge alone won’t tell you substantially.
With that caveat, here’s some knowledge, with glucose measurements on the left axis and managing speed (measured with a Wahoo GPS watch) on the correct axis:
March 28: Simple 7.5-Mile Run
This was an quick operate with a pal at about 8:00/mile speed, and the knowledge is pretty normal of what I observed in the initial month or so of donning a CGM. But there is a dilemma with the knowledge. You can see the minute-by-minute updates when I’m taking in my pre-operate banana. But when the operate starts, I’m only obtaining readings every single fifteen minutes. That’s simply because I left my cellular phone at the rear of, and the CGM by itself only data readings every single fifteen minutes, which are then uploaded to your cellular phone next time you hook up. So this sample may possibly be missing some significant fluctuations through the operate.
Supersapiens has since introduced a focused wrist reader for men and women like me who hate managing with their telephones. But when I realized the dilemma, I borrowed a pink narwhal fanny pack from my daughter and started off having my cellular phone alongside.
April 8: Interval Work out
With my cellular phone in my pocket, I now see a great deal much more motion in the knowledge. This exercise consisted of a fifteen-minute warm-up 4 sets of (approximately) 1:00 hard, 1:00 quick, three:00 hard, 1:30 quick fifteen-minute amazing-down. During the hard portion of the exercise, you can see my glucose concentrations climbing like a staircase.
This was attention-grabbing to me, simply because the simplistic way of pondering about a CGM is that it’s a fuel gauge, telling you how substantially juice you’ve got left in the tank. That’s clearly not the situation in this context: the more challenging I go, the higher my glucose climbs, creating a pleasant staircase sample. As my muscle groups start burning by means of fuel much more quickly, more power from reserve tanks like the carbohydrate stored in my liver is getting introduced into the bloodstream to continue to keep me sprinting.
Then, when I finish my intervals and start jogging gradually property, my blood sugar remains sky-substantial (anything at all previously mentioned a hundred and forty is regarded unusually substantial) simply because I’ve ramped up my fuel procedure but am no extended functioning as hard.
Those people readings of one hundred seventy at the finish of my exercise are surely substantial, but possible nothing to be nervous about, Sprouse says. One particular superior sign: as quickly as the exercise finishes, they fall extremely quickly into a much more ordinary range. That possible suggests that my physique didn’t need to produce a spike of insulin to convey my blood sugar back down. If I’d taken a gel or other fuel through that exercise (which I didn’t), Sprouse would have endorsed me not to bother, as my glucose concentrations were already substantial enough.
Might eighteen: Zoom Presentation
On this specific working day, I gave an online presentation to a non-earnings team. It was just fifteen minutes long, for a little and friendly viewers. But hey, I even now get nervous. It was intriguing to see how everyday living occasions, and psychological condition much more frequently, afflicted my blood sugar concentrations. In the context of physical exercise, assume about the difference involving an quick operate, a hard exercise, and an significant race. Your speed is different, but so are your worry concentrations. In the interval exercise previously mentioned, how substantially of that staircase influence was feedback (my muscle groups need much more glucose) and how substantially was feedforward (my brain is on substantial notify, mobilizing bodily assets in anticipation of requires)?
It is also attention-grabbing to see the crash later on. I normally sense like a squeezed-out sponge following offering a communicate here’s the physiological correlate. Levels below 70 are regarded unusually very low. How did I reply? Likely by taking in anything sweet, for this reason the subsequent spike at close to three P.M. (For the initial month or so of donning a CGM, I dutifully entered every single food and snack into the Supersapiens application, but by this point the novelty had worn off and I was largely only recording pre-exercise foods.)
Might 20: forty two-Mile Bicycle Trip
I’m not substantially of a bike owner, but one of the situations I wanted to check with the CGM was an extended exercise exactly where I may possibly conceivably bonk. Would the sensation of hitting the wall in fact correspond with an unusually very low blood sugar examining? It doesn’t usually, Sprouse instructed me: “We’ve all imagined we were bonking and definitely we just weren’t extremely in shape.”
I organized to go for a 4-hour trip with a pal, largely at a peaceful speed. The exception was the initial 20 minutes or so, when I rode hard simply because I was late for our conference, and the last 50 % hour, when I rode hard just for the heck of it. In this graph, the correct-hand axis is my coronary heart amount alternatively of speed.
The in general picture is approximately what you’d be expecting, Sprouse says. Glucose concentrations are fairly steady through the principal aspect of the trip, but step by step start to edge downwards following about 1.5 to 2 several hours. I intentionally didn’t fuel at all through this aspect of the trip, to see how very low I’d go. When we eventually stopped for a small crack following close to 3 several hours of using, my glucose concentrations dipped all the way down below 70. Then I hit them with a gel and a Larabar, totaling 50 grams of carbs, and you can see my blood sugar immediately reply with a big spike.
About 50 % an hour following the fuel surge, I break up off from my pal and started off hammering property. One particular unanswered problem is irrespective of whether my blood sugar was heading to plunge adhering to the spike no issue what, or irrespective of whether the plunge was precipitated in aspect by the simple fact that my muscle groups all of a sudden started off burning fuel much more promptly. My suspicion is that the principal minimize is a response to the sugar-fueled spike—but then, with about ten minutes left in the trip, I started off heading uphill for the final extend. At that point, you can see my coronary heart amount spike, and the blood sugar concentrations briefly boost once again, just as they did through the toughest pieces of my interval exercise.
Sprouse’s just take, phrased much more politely, was that I’d fueled like an fool for this trip: nothing at all for 3 several hours, and then mainlining a major bolus of sugar. (He recognized, when I discussed, that I was striving to produce excessive values with the CGM.) If I in fact wanted to optimize performance, he reported, the graph prompt that I would not have necessary any fuel for a trip like this lasting up to probably two several hours. For the extended trip, I would benefit from scaled-down, much more frequent doses of fuel—perhaps 50 % a banana in this article, a several sips of sports drink there, and so on.
Might 23: 7-Mile Simple Run
This was one more Sunday morning quick operate, extremely equivalent to the one from March 28 except that I brought my cellular phone with me to get appropriate knowledge. But this time, my blood sugar concentrations are swinging close to wildly. As with the bike trip, this was partly by layout. Normally I consume little or nothing in advance of heading out for a morning operate. This time, I had a peanut-butter-and-honey sandwich—because I realized it would mess with my blood sugar.
For as long as I can recall, I’ve seasoned anything named rebound hypoglycemia. If I consume anything, specially if it’s carb-large, 30 to 60 minutes in advance of a morning operate, then fifteen minutes into the operate I’ll start sensation light-weight-headed. It’ll last five to ten minutes, then disappear. What is taking place, I’ve gathered, is that my breakfast or snack triggers a delayed insulin response that kicks in approximately when I’m commencing my operate. Both of those insulin and physical exercise are then striving to lessen my blood sugar, and it overshoots in advance of obtaining well balanced out.
I wanted to see this in motion, for this reason the sandwich. You can see that my concentrations are mounting sharply in advance of I even start managing. Then following about ten minutes of managing, they start dropping. On this specific operate, I didn’t get the entire light-weight-headedness, but did sense pretty sluggish for a when. Then the concentrations finally stabilize at a suitably elevated amount for the relaxation of the operate.
Sprouse’s information for this scenario caught me off-guard: he prompt throwing in a temporary dash. Just as through my interval exercise (or even my online communicate), ramping up the exertion and adrenaline will jolt your blood sugar upward. Apparently, he reported that through the Tour de France, he tells riders not to have a final pre-race food in the pair of several hours in advance of levels that start with an uphill, since they may possibly need to be ready to go hard correct from the gun. For in the beginning flat levels, which typically start by noodling close to carefully, they can go in advance with the more food two to 3 several hours before—but then continue to keep gels ready in situation they need a increase early in the stage.
So what’s the in general takeaway from all this? To be truthful, I didn’t get a probability to set the gadget by means of its appropriate paces. This was mid-pandemic, when races were canceled and my 4- and six-yr-olds were the two understanding from property. I had issues slipping away to educate for much more than 50 % an hour at a time, and when I did I was not placing the entire world on fire. You can see the blood sugar spikes from when I was waking up in the middle of the night and stressing about the condition of the entire world.
Continue to, there are some glimmers of the CGM’s probable: for dialing in the fueling on long rides, for figuring out how to stay clear of rebound hypoglycemia, and for looking at the way my physique reacts to worry. That reported, as Sprouse pointed out, you definitely need to zoom out from particular person routines to see the 24-hour context, and the everyday or weekly patterns. That’s a great deal of knowledge to sift by means of, and Supersapiens’ major challenge (which they’ve been chipping away at since my trial operate finished in June) is to translate it into digestible and actionable advice—even for individuals of us who really don’t have an individual like Sprouse on speed dial.
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