5 Insights from Training with a Continuous Glucose Monitor


Previous 12 months, though reporting this report on the rising pattern of endurance athletes working with constant glucose displays (CGMs), I tried it myself for two months. The preliminary article focused on the science (sparse although it is) driving statements that figuring out what your blood sugar is executing at any supplied instant can enable you gas extra efficiently and accomplish improved. But I figured it would be fun to share some of my real CGM data—so what follows are 5 agent samples that illustrate some of my ordeals.

To assist me interpret this details, I named Kevin Sprouse, a athletics drugs medical professional in Knoxville who also serves as head of medication for the EF Education-Nippo pro cycling group. Sprouse employs CGMs with his Tour de France cyclists (although not all through levels of competition), as properly as with leisure athletes in cycling and other sporting activities.

To start out, I emailed him some training data—which, it turns out, is completely the mistaken approach. “It’s seriously crucial to seem at the 24-hour period of time close to the training,” he defined when we talked. “Looking at just the exercise is a mistake. It is myopic.” Lower blood sugar for the duration of a exercise session may well be the end result of a lousy supper the night time just before. Large blood sugar may well just reveal that you didn’t get enough snooze. Without those people contextual clues, the training facts alone will not convey to you a lot.

With that caveat, here’s some info, with glucose measurements on the still left axis and running velocity (measured with a Wahoo GPS enjoy) on the right axis:

March 28: Quick 7.5-Mile Operate

This was an quick run with a friend at about 8:00/mile pace, and the information is fairly typical of what I noticed in the initially thirty day period or so of carrying a CGM. But there’s a difficulty with the facts. You can see the minute-by-minute updates when I’m feeding on my pre-operate banana. But the moment the run begins, I’m only obtaining readings each individual 15 minutes. That’s due to the fact I left my telephone behind, and the CGM alone only data readings just about every 15 minutes, which are then uploaded to your mobile phone following time you connect. So this pattern might be missing some crucial fluctuations through the operate.

Supersapiens has due to the fact introduced a dedicated wrist reader for people like me who dislike working with their phones. But as soon as I realized the challenge, I borrowed a pink narwhal fanny pack from my daughter and begun having my telephone together.

April 8: Interval Workout

With my telephone in my pocket, I now see a whole lot additional action in the data. This work out consisted of a 15-minute heat-up four sets of (roughly) 1:00 tough, 1:00 quick, 3:00 challenging, 1:30 uncomplicated 15-moment cool-down. For the duration of the challenging portion of the training, you can see my glucose concentrations climbing like a staircase.

This was appealing to me, due to the fact the simplistic way of thinking about a CGM is that it is a gasoline gauge, telling you how significantly juice you have obtained still left in the tank. That’s obviously not the case in this context: the more challenging I go, the increased my glucose climbs, making a good staircase pattern. As my muscle mass start burning via gasoline much more swiftly, excess power from reserve tanks like the carbohydrate saved in my liver is being launched into the bloodstream to maintain me sprinting.

Then, when I complete my intervals and start jogging slowly but surely residence, my blood sugar stays sky-higher (anything at all above 140 is regarded unusually superior) mainly because I have ramped up my fuel method but am no more time performing as difficult.

All those readings of 170 at the conclusion of my workout are unquestionably substantial, but probable practically nothing to be worried about, Sprouse suggests. A single excellent sign: as quickly as the exercise session ends, they drop really promptly into a far more typical assortment. That probable indicates that my overall body did not need to produce a spike of insulin to convey my blood sugar again down. If I’d taken a gel or other gasoline for the duration of that training (which I did not), Sprouse would have recommended me not to bother, as my glucose levels were being already high plenty of.

May possibly 18: Zoom Presentation

On this individual day, I gave an online presentation to a non-income group. It was just 15 minutes very long, for a compact and welcoming viewers. But hey, I even now get anxious. It was fascinating to see how life occasions, and psychological point out additional normally, affected my blood sugar ranges. In the context of workout, think about the variation concerning an straightforward run, a really hard workout, and an important race. Your rate is different, but so are your worry stages. In the interval exercise session over, how significantly of that staircase influence was feedback (my muscle groups need additional glucose) and how considerably was feedforward (my brain is on substantial alert, mobilizing bodily sources in anticipation of needs)?

It is also interesting to see the crash afterwards. I generally feel like a squeezed-out sponge just after providing a discuss here’s the physiological correlate. Ranges beneath 70 are viewed as unusually low. How did I react? Probably by eating some thing sweet, consequently the subsequent spike at about 3 P.M. (For the to start with thirty day period or so of donning a CGM, I dutifully entered every single food and snack into the Supersapiens application, but by this position the novelty had worn off and I was generally only recording pre-exercise foods.)

Could 20: 42-Mile Bicycle Trip

I’m not substantially of a bicycle owner, but just one of the conditions I wished to examination with the CGM was an extended exercise in which I might conceivably bonk. Would the feeling of hitting the wall basically correspond with an unusually reduced blood sugar reading? It does not constantly, Sprouse instructed me: “We’ve all considered we were being bonking and seriously we just weren’t really fit.”

I organized to go for a 4-hour ride with a pal, mainly at a peaceful speed. The exception was the 1st 20 minutes or so, when I rode really hard mainly because I was late for our meeting, and the past fifty percent hour, when I rode tricky just for the heck of it. In this graph, the suitable-hand axis is my heart fee instead of speed.

The over-all photograph is around what you’d anticipate, Sprouse states. Glucose stages are somewhat secure throughout the primary element of the trip, but slowly start off to edge downwards after about 1.5 to 2 several hours. I intentionally didn’t gasoline at all for the duration of this component of the journey, to see how low I’d go. When we eventually stopped for a shorter crack just after all-around 3 hrs of riding, my glucose ranges dipped all the way down below 70. Then I strike them with a gel and a Larabar, totaling 50 grams of carbs, and you can see my blood sugar instantaneously reply with a big spike.

About 50 percent an hour immediately after the fuel surge, I break up off from my friend and started out hammering house. Just one unanswered dilemma is no matter if my blood sugar was heading to plunge adhering to the spike no subject what, or no matter if the plunge was precipitated in component by the truth that my muscles suddenly begun burning gasoline extra rapidly. My suspicion is that the most important reduce is a response to the sugar-fueled spike—but then, with about 10 minutes left in the journey, I began heading uphill for the closing stretch. At that stage, you can see my heart charge spike, and the blood sugar stages briefly boost again, just as they did all through the toughest parts of my interval exercise.

Sprouse’s choose, phrased a lot more politely, was that I’d fueled like an fool for this experience: practically nothing at all for three several hours, and then mainlining a large bolus of sugar. (He comprehended, when I defined, that I was attempting to create severe values with the CGM.) If I in fact wished to improve effectiveness, he explained, the graph proposed that I would not have required any gasoline for a trip like this lasting up to most likely two hrs. For the more time ride, I would reward from smaller, more recurrent doses of fuel—perhaps half a banana listed here, a few sips of sports consume there, and so on.

May perhaps 23: 7-Mile Uncomplicated Run

CGM data May 23

This was yet another Sunday early morning effortless operate, really very similar to the one from March 28 besides that I brought my cell phone with me to get proper info. But this time, my blood sugar concentrations are swinging all-around wildly. As with the bike journey, this was partly by layout. Commonly I consume very little or almost nothing just before heading out for a early morning run. This time, I experienced a peanut-butter-and-honey sandwich—because I understood it would mess with my blood sugar.

For as very long as I can remember, I have knowledgeable a thing called rebound hypoglycemia. If I try to eat a little something, significantly if it’s carb-weighty, 30 to 60 minutes prior to a early morning operate, then 15 minutes into the run I’ll begin experience mild-headed. It’ll previous 5 to ten minutes, then vanish. What’s taking place, I’ve collected, is that my breakfast or snack triggers a delayed insulin reaction that kicks in approximately when I’m starting off my run. Each insulin and exercise are then attempting to decreased my blood sugar, and it overshoots before having well balanced out.

I wished to see this in motion, that’s why the sandwich. You can see that my concentrations are mounting sharply right before I even start off jogging. Then immediately after about ten minutes of functioning, they commence dropping. On this individual run, I didn’t get the complete light-headedness, but did truly feel really sluggish for a whilst. Then the degrees finally stabilize at a suitably elevated stage for the rest of the run.

Sprouse’s information for this predicament caught me off-guard: he instructed throwing in a transient dash. Just as for the duration of my interval exercise session (or even my on-line speak), ramping up the work and adrenaline will jolt your blood sugar upward. Interestingly, he reported that for the duration of the Tour de France, he tells riders not to have a remaining pre-race meal in the pair of several hours in advance of stages that commence with an uphill, considering that they may require to be all set to go hard correct from the gun. For originally flat levels, which generally start off by noodling all over carefully, they can go ahead with the excess food two to three hrs before—but then continue to keep gels completely ready in circumstance they have to have a raise early in the phase.

So what is the total takeaway from all this? To be truthful, I did not get a opportunity to set the unit via its proper paces. This was mid-pandemic, when races had been canceled and my four- and six-year-olds ended up each understanding from house. I experienced issues slipping absent to coach for a lot more than 50 % an hour at a time, and when I did I was not setting the world on fire. You can see the blood sugar spikes from when I was waking up in the middle of the night time and worrying about the condition of the globe.

Even now, there are some glimmers of the CGM’s potential: for dialing in the fueling on lengthy rides, for figuring out how to prevent rebound hypoglycemia, and for observing the way my human body reacts to pressure. That claimed, as Sprouse pointed out, you genuinely want to zoom out from particular person exercise sessions to see the 24-hour context, and the everyday or weekly styles. That’s a lot of knowledge to sift through, and Supersapiens’ huge obstacle (which they’ve been chipping away at considering that my trial run ended in June) is to translate it into digestible and actionable advice—even for individuals of us who do not have anyone like Sprouse on pace dial.

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