5 Insights from Training with a Continuous Glucose Monitor

Robert S. Hays


Final 12 months, though reporting this posting on the rising development of stamina athletes applying steady glucose displays (CGMs), I tried using it myself for two months. The initial post concentrated on the science (sparse though it is) at the rear of promises that knowing what your blood sugar is accomplishing at any given moment can assistance you gas a lot more effectively and complete far better. But I figured it would be exciting to share some of my genuine CGM data—so what follows are 5 agent samples that illustrate some of my encounters.

To assistance me interpret this knowledge, I called Kevin Sprouse, a sports drugs health care provider in Knoxville who also serves as head of medication for the EF Schooling-Nippo pro biking crew. Sprouse employs CGMs with his Tour de France cyclists (while not for the duration of competition), as properly as with recreational athletes in cycling and other athletics.

To commence, I emailed him some training data—which, it turns out, is absolutely the improper approach. “It’s definitely vital to appear at the 24-hour period all around the exercise routine,” he spelled out when we talked. “Looking at just the workout is a blunder. It is myopic.” Reduced blood sugar all through a exercise session might be the consequence of a terrible supper the night prior to. Superior blood sugar could just reveal that you didn’t get sufficient sleep. Without having individuals contextual clues, the work out facts on your own will not explain to you much.

With that caveat, here’s some info, with glucose measurements on the still left axis and jogging pace (calculated with a Wahoo GPS enjoy) on the correct axis:

March 28: Simple 7.5-Mile Run

This was an effortless operate with a friend at about 8:00/mile rate, and the data is quite regular of what I observed in the to start with month or so of donning a CGM. But there’s a problem with the details. You can see the moment-by-moment updates when I’m feeding on my pre-operate banana. But after the run commences, I’m only acquiring readings every 15 minutes. That is for the reason that I remaining my cellular phone behind, and the CGM by itself only records readings each and every 15 minutes, which are then uploaded to your cellphone up coming time you join. So this sample may be lacking some vital fluctuations through the run.

Supersapiens has since launched a dedicated wrist reader for people today like me who dislike running with their phones. But once I recognized the dilemma, I borrowed a pink narwhal fanny pack from my daughter and commenced using my cellphone along.

April 8: Interval Work out

With my cellular phone in my pocket, I now see a good deal far more action in the knowledge. This work out consisted of a 15-minute heat-up 4 sets of (roughly) 1:00 challenging, 1:00 straightforward, 3:00 challenging, 1:30 straightforward 15-minute cool-down. Through the tricky part of the exercise, you can see my glucose stages 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 substantially juice you have received remaining in the tank. That is plainly not the scenario in this context: the tougher I go, the bigger my glucose climbs, creating a great staircase pattern. As my muscle tissues start burning through gasoline a lot more fast, more vitality from reserve tanks like the carbohydrate stored in my liver is remaining produced into the bloodstream to preserve me sprinting.

Then, when I end my intervals and start jogging slowly house, my blood sugar continues to be sky-substantial (everything above 140 is considered unusually significant) since I have ramped up my gas program but am no more time functioning as really hard.

Individuals readings of 170 at the conclusion of my exercise session are absolutely large, but likely practically nothing to be nervous about, Sprouse claims. Just one excellent indicator: as shortly as the workout ends, they fall pretty rapidly into a more regular array. That very likely indicates that my overall body didn’t require to make a spike of insulin to convey my blood sugar again down. If I’d taken a gel or other fuel for the duration of that exercise routine (which I didn’t), Sprouse would have recommended me not to trouble, as my glucose ranges had been presently large enough.

May possibly 18: Zoom Presentation

On this distinct working day, I gave an on the web presentation to a non-gain group. It was just 15 minutes extended, for a little and helpful viewers. But hey, I nevertheless get nervous. It was intriguing to see how daily life gatherings, and psychological condition more usually, afflicted my blood sugar stages. In the context of workout, consider about the change involving an effortless operate, a really hard work out, and an vital race. Your pace is various, but so are your strain concentrations. In the interval work out over, how considerably of that staircase outcome was suggestions (my muscle groups have to have far more glucose) and how a lot was feedforward (my mind is on substantial warn, mobilizing bodily sources in anticipation of requires)?

It’s also intriguing to see the crash later on. I frequently come to feel like a squeezed-out sponge right after giving a communicate here’s the physiological correlate. Concentrations below 70 are viewed as unusually lower. How did I respond? Almost certainly by consuming one thing sweet, that’s why the subsequent spike at all over 3 P.M. (For the initially thirty day period or so of donning a CGM, I dutifully entered each individual meal and snack into the Supersapiens application, but by this point the novelty experienced worn off and I was largely only recording pre-exercise routine meals.)

Could 20: 42-Mile Bike Journey

I’m not considerably of a bicycle owner, but a single of the cases I needed to take a look at with the CGM was an prolonged workout where by I might conceivably bonk. Would the emotion of hitting the wall really correspond with an unusually small blood sugar examining? It does not always, Sprouse explained to me: “We’ve all thought we had been bonking and actually we just weren’t really suit.”

I organized to go for a four-hour experience with a mate, typically at a relaxed pace. The exception was the very first 20 minutes or so, when I rode hard since I was late for our conference, and the previous 50 percent hour, when I rode challenging just for the heck of it. In this graph, the proper-hand axis is my coronary heart level instead of speed.

The over-all picture is roughly what you’d assume, Sprouse claims. Glucose amounts are fairly secure in the course of the principal part of the experience, but gradually start out to edge downwards immediately after about 1.5 to 2 hours. I intentionally did not fuel at all through this portion of the ride, to see how reduced I’d go. When we eventually stopped for a quick break soon after all around a few several hours of riding, my glucose amounts dipped all the way down under 70. Then I hit them with a gel and a Larabar, totaling 50 grams of carbs, and you can see my blood sugar instantly answer with a huge spike.

About 50 percent an hour right after the gas surge, I split off from my buddy and started off hammering dwelling. 1 unanswered problem is regardless of whether my blood sugar was going to plunge adhering to the spike no matter what, or whether or not the plunge was precipitated in section by the fact that my muscles suddenly began burning gas more rapidly. My suspicion is that the primary lower is a response to the sugar-fueled spike—but then, with about 10 minutes left in the experience, I started heading uphill for the closing extend. At that stage, you can see my coronary heart rate spike, and the blood sugar stages briefly increase yet again, just as they did through the toughest sections of my interval training.

Sprouse’s acquire, phrased more politely, was that I’d fueled like an fool for this journey: absolutely nothing at all for 3 hrs, and then mainlining a major bolus of sugar. (He recognized, when I stated, that I was seeking to develop extraordinary values with the CGM.) If I truly wanted to enhance performance, he explained, the graph advised that I would not have desired any gasoline for a ride like this long lasting up to perhaps two hrs. For the more time experience, I would advantage from lesser, additional recurrent doses of fuel—perhaps 50 percent a banana listed here, a number of sips of sports activities drink there, and so on.

Might 23: 7-Mile Effortless Operate

CGM data May 23

This was an additional Sunday morning effortless operate, quite equivalent to the a single from March 28 other than that I brought my phone with me to get proper knowledge. But this time, my blood sugar ranges are swinging all over wildly. As with the bicycle journey, this was partly by style and design. Usually I eat minor or practically nothing just before heading out for a early morning run. This time, I experienced a peanut-butter-and-honey sandwich—because I knew it would mess with my blood sugar.

For as prolonged as I can keep in mind, I have experienced a little something called rebound hypoglycemia. If I take in some thing, particularly if it is carb-large, 30 to 60 minutes ahead of a morning operate, then 15 minutes into the operate I’ll get started experience light-weight-headed. It’ll final five to ten minutes, then disappear. What is occurring, I have collected, is that my breakfast or snack triggers a delayed insulin reaction that kicks in about when I’m starting my run. The two insulin and exercising are then trying to reduced my blood sugar, and it overshoots prior to receiving balanced out.

I desired to see this in action, consequently the sandwich. You can see that my concentrations are soaring sharply prior to I even start off managing. Then immediately after about 10 minutes of operating, they start dropping. On this particular run, I did not get the whole mild-headedness, but did sense pretty sluggish for a although. Then the degrees inevitably stabilize at a suitably elevated degree for the rest of the operate.

Sprouse’s advice for this predicament caught me off-guard: he advised throwing in a quick dash. Just as throughout my interval training (or even my on the net converse), ramping up the work and adrenaline will jolt your blood sugar upward. Apparently, he explained that in the course of the Tour de France, he tells riders not to have a last pre-race food in the few of hrs right before phases that start with an uphill, because they may will need to be completely ready to go challenging ideal from the gun. For to begin with flat stages, which commonly get started by noodling all around carefully, they can go in advance with the more meal two to 3 hrs before—but then preserve gels all set in scenario they need to have a enhance early in the phase.

So what’s the all round takeaway from all this? To be sincere, I didn’t get a likelihood to place the system by way of its right paces. This was mid-pandemic, when races have been canceled and my 4- and six-yr-olds were being each discovering from house. I had difficulty slipping away to educate for extra than fifty percent an hour at a time, and when I did I was not setting the entire world on fireplace. You can see the blood sugar spikes from when I was waking up in the center of the night and worrying about the point out of the planet.

Even now, there are some glimmers of the CGM’s probable: for dialing in the fueling on extended rides, for figuring out how to keep away from rebound hypoglycemia, and for seeing the way my entire body reacts to strain. That claimed, as Sprouse pointed out, you definitely have to have to zoom out from particular person exercise routines to see the 24-hour context, and the everyday or weekly designs. Which is a lot of information to sift by, and Supersapiens’ big obstacle (which they’ve been chipping absent at since my demo run ended in June) is to translate it into digestible and actionable advice—even for those people of us who really don’t have someone like Sprouse on speed dial.

For a lot more Sweat Science, be part of me on Twitter and Facebook, signal up for the e mail newsletter, and verify out my e-book Endure: Mind, System, and the Curiously Elastic Boundaries of Human General performance.

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