December 7, 2022

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5 Insights from Training with a Continuous Glucose Monitor


Last year, when reporting this report on the emerging craze of endurance athletes working with constant glucose screens (CGMs), I experimented with it myself for two months. The initial report centered on the science (sparse while it is) at the rear of claims that knowing what your blood sugar is executing at any offered instant can aid you gas much more efficiently and execute greater. But I figured it would be enjoyable to share some of my real CGM data—so what follows are 5 agent samples that illustrate some of my ordeals.

To aid me interpret this details, I called Kevin Sprouse, a athletics medicine medical doctor in Knoxville who also serves as head of medicine for the EF Instruction-Nippo pro cycling workforce. Sprouse employs CGMs with his Tour de France cyclists (while not during opposition), as perfectly as with recreational athletes in cycling and other athletics.

To begin, I emailed him some exercise data—which, it turns out, is fully the erroneous strategy. “It’s seriously essential to search at the 24-hour period of time all around the exercise,” he discussed when we talked. “Looking at just the exercise is a blunder. It is myopic.” Small blood sugar during a exercise might be the result of a bad evening meal the evening just before. Superior blood sugar might just reveal that you didn’t get enough rest. Without all those contextual clues, the exercise details on your own will not inform you a lot.

With that caveat, here’s some details, with glucose measurements on the remaining axis and operating pace (measured with a Wahoo GPS view) on the appropriate axis:

March 28: Simple seven.5-Mile Run

This was an easy operate with a pal at about eight:00/mile rate, and the details is pretty regular of what I saw in the initial month or so of donning a CGM. But there is a problem with the details. You can see the moment-by-moment updates when I’m consuming my pre-operate banana. But the moment the operate starts off, I’m only getting readings just about every 15 minutes. That is since I remaining my telephone at the rear of, and the CGM itself only documents readings just about every 15 minutes, which are then uploaded to your telephone following time you connect. So this sample may well be lacking some essential fluctuations during the operate.

Supersapiens has due to the fact introduced a devoted wrist reader for folks like me who loathe operating with their telephones. But the moment I understood the problem, I borrowed a pink narwhal fanny pack from my daughter and commenced taking my telephone together.

April eight: Interval Workout

With my telephone in my pocket, I now see a large amount much more action in the details. This exercise consisted of a 15-moment warm-up four sets of (approximately) one:00 tough, one:00 easy, three:00 tough, one:30 easy 15-moment great-down. Throughout the tough portion of the exercise, you can see my glucose stages climbing like a staircase.

This was exciting to me, since the simplistic way of wondering about a CGM is that it’s a gas gauge, telling you how a lot juice you’ve got remaining in the tank. That is obviously not the case in this context: the more challenging I go, the bigger my glucose climbs, generating a pleasant staircase sample. As my muscle tissue begin burning as a result of gas much more promptly, further strength from reserve tanks like the carbohydrate stored in my liver is being produced into the bloodstream to preserve me sprinting.

Then, when I finish my intervals and begin jogging little by little house, my blood sugar stays sky-higher (anything at all higher than 140 is regarded as unusually higher) since I’ve ramped up my gas system but am no more time performing as tough.

Those people readings of one hundred seventy at the conclusion of my exercise are undoubtedly higher, but possible very little to be worried about, Sprouse suggests. One particular superior sign: as quickly as the exercise ends, they drop incredibly promptly into a much more regular selection. That possible suggests that my overall body didn’t want to create a spike of insulin to provide my blood sugar again down. If I’d taken a gel or other gas during that exercise (which I didn’t), Sprouse would have endorsed me not to hassle, as my glucose stages had been previously higher enough.

Could 18: Zoom Presentation

On this particular day, I gave an on the web presentation to a non-gain group. It was just 15 minutes very long, for a little and pleasant viewers. But hey, I however get anxious. It was interesting to see how lifestyle gatherings, and mental condition much more normally, influenced my blood sugar stages. In the context of physical exercise, believe about the change in between an easy operate, a tough exercise, and an essential race. Your rate is various, but so are your strain stages. In the interval exercise higher than, how a lot of that staircase result was opinions (my muscle tissue want much more glucose) and how a lot was feedforward (my mind is on higher inform, mobilizing bodily assets in anticipation of requires)?

It is also exciting to see the crash afterwards. I frequently sense like a squeezed-out sponge immediately after supplying a converse here’s the physiological correlate. Levels beneath 70 are regarded as unusually low. How did I respond? Most likely by consuming anything sweet, hence the subsequent spike at all around three P.M. (For the initial month or so of donning a CGM, I dutifully entered just about every meal and snack into the Supersapiens app, but by this position the novelty experienced worn off and I was mainly only recording pre-exercise meals.)

Could 20: forty two-Mile Bicycle Trip

I’m not a lot of a bike owner, but one particular of the cases I needed to exam with the CGM was an prolonged exercise where by I might conceivably bonk. Would the feeling of hitting the wall in fact correspond with an unusually low blood sugar studying? It doesn’t generally, Sprouse informed me: “We’ve all believed we had been bonking and seriously we just weren’t incredibly match.”

I arranged to go for a four-hour trip with a pal, mainly at a calm rate. The exception was the initial 20 minutes or so, when I rode tough since I was late for our meeting, and the last fifty percent hour, when I rode tough just for the heck of it. In this graph, the appropriate-hand axis is my heart fee rather of pace.

The in general picture is approximately what you’d be expecting, Sprouse suggests. Glucose stages are reasonably steady during the most important portion of the trip, but steadily begin to edge downwards immediately after about one.5 to 2 hrs. I deliberately didn’t gas at all during this portion of the trip, to see how low I’d go. When we eventually stopped for a small break immediately after all around a few hrs of driving, my glucose stages dipped all the way down beneath 70. Then I strike them with a gel and a Larabar, totaling fifty grams of carbs, and you can see my blood sugar immediately respond with a large spike.

About fifty percent an hour immediately after the gas surge, I break up off from my pal and commenced hammering house. One particular unanswered question is no matter if my blood sugar was heading to plunge pursuing the spike no issue what, or no matter if the plunge was precipitated in portion by the reality that my muscle tissue suddenly commenced burning gas much more promptly. My suspicion is that the most important minimize is a reaction to the sugar-fueled spike—but then, with about 10 minutes remaining in the trip, I commenced heading uphill for the last stretch. At that position, you can see my heart fee spike, and the blood sugar stages briefly improve yet again, just as they did during the most difficult areas of my interval exercise.

Sprouse’s get, phrased much more politely, was that I’d fueled like an idiot for this trip: very little at all for a few hrs, and then mainlining a big bolus of sugar. (He comprehended, when I discussed, that I was striving to create serious values with the CGM.) If I in fact needed to improve efficiency, he reported, the graph prompt that I wouldn’t have wanted any gas for a trip like this long lasting up to maybe two hrs. For the more time trip, I would profit from scaled-down, much more repeated doses of fuel—perhaps fifty percent a banana in this article, a couple sips of athletics consume there, and so on.

Could 23: seven-Mile Simple Run

CGM data May 23

This was yet another Sunday early morning easy operate, incredibly similar to the one particular from March 28 except that I introduced my telephone with me to get good details. But this time, my blood sugar stages are swinging all around wildly. As with the bicycle trip, this was partly by style. Ordinarily I eat small or very little just before heading out for a early morning operate. This time, I experienced a peanut-butter-and-honey sandwich—because I realized it would mess with my blood sugar.

For as very long as I can recall, I’ve experienced anything called rebound hypoglycemia. If I eat anything, specifically if it’s carb-large, 30 to sixty minutes just before a early morning operate, then 15 minutes into the operate I’ll begin feeling gentle-headed. It’ll last 5 to 10 minutes, then vanish. What’s occurring, I’ve collected, is that my breakfast or snack triggers a delayed insulin reaction that kicks in approximately when I’m starting my operate. Both insulin and physical exercise are then striving to reduce my blood sugar, and it overshoots just before getting balanced out.

I needed to see this in action, hence the sandwich. You can see that my stages are soaring sharply just before I even begin operating. Then immediately after about 10 minutes of operating, they begin dropping. On this particular operate, I didn’t get the comprehensive gentle-headedness, but did sense pretty sluggish for a when. Then the stages inevitably stabilize at a suitably elevated degree for the rest of the operate.

Sprouse’s advice for this condition caught me off-guard: he prompt throwing in a quick sprint. Just as during my interval exercise (or even my on the web converse), ramping up the effort and adrenaline will jolt your blood sugar upward. Curiously, he reported that during the Tour de France, he tells riders not to have a last pre-race meal in the few of hrs just before stages that begin with an uphill, due to the fact they may well want to be prepared to go tough appropriate from the gun. For in the beginning flat stages, which generally begin by noodling all around carefully, they can go forward with the further meal two to a few hrs before—but then preserve gels prepared in case they want a improve early in the stage.

So what’s the in general takeaway from all this? To be genuine, I didn’t get a opportunity to put the system as a result of its good paces. This was mid-pandemic, when races had been canceled and my four- and 6-year-olds had been both discovering from house. I experienced difficulties slipping away to prepare for much more than fifty percent an hour at a time, and when I did I wasn’t placing the globe on fireplace. You can see the blood sugar spikes from when I was waking up in the center of the evening and stressing about the condition of the globe.

Still, there are some glimmers of the CGM’s possible: for dialing in the fueling on very long rides, for figuring out how to avoid rebound hypoglycemia, and for observing the way my overall body reacts to strain. That reported, as Sprouse pointed out, you seriously want to zoom out from person exercise sessions to see the 24-hour context, and the each day or weekly styles. That is a large amount of details to sift as a result of, and Supersapiens’ big challenge (which they’ve been chipping away at due to the fact my trial operate finished in June) is to translate it into digestible and actionable advice—even for all those of us who do not have anyone like Sprouse on pace dial.

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