Mike Hoskins

I step outside to take a quick walk around the block at lunchtime and see my blood sugar is hovering at 98 mg/dL -- just high enough so it might not drop too low, but just low enough so danger lurks. My Dexcom CGM trend arrow is level, and it's showing a flat line for most of the morning post-breakfast.

"It's just a quick walk with the dog -- nothing too heavy, so I should be OK," I tell myself.

Roughly around the halfway point before we even make the turn back toward my house, it's clear that I was wrong. The hypo symptoms begin to set, thanks to a 25-point drop in glucose level that magically hit over the past 15 minutes. So I dig into the orange-flavored glucose tabs in my pocket.

In my world, this unpredictable Exercise Effect happens more than I'd care to admit. No matter whether it's a quick dog walk around the block, more intense bike riding or outdoor yard work, I always have my blood sugars on the brain, and I'm often wrong in guesstimating how they will react. In a perfect world, I'd love to have some piece of technology that could predict what my blood sugars would do based on the length and intensity of exercise I am about to undertake, and also tell me if there's a need for insulin or food based on that prediction.

With all that in mind, I set out to find some kind of "predictor" tool that might help me better manage exercise. What I found were three options that can best be described as "The Good, The Bad, and the Unavailable But On the Horizon."

The Good

Leading the way on this seems to be the William Sansum Diabetes Center in Santa Barbara, CA, which recently rolled out the updated version of an online resource called ExCarbs. We heard about this earlier in the year, when we connected with the new head of innovation and research Dr. David Kerr, who joined Sansum from the UK (where he originally developed ExCarbs).

ExCarbs is an online tool -- not yet available in mobile format -- that aims "to help people with diabetes using insulin to feel comfortable with taking up exercise." The site specifically states: "our advice is not aimed at elite athletes but hopefully covers the basic rules for most people living with diabetes."

Using the site's "Exercise Intensity Calculator" on the home page, you plug in personal details -- weight, insulin-to-carb ratio, total daily units of insulin, how long you plan to exercise and how intense it will be -- and click the blue "Help Me Exercise Safely" tab. The calculator spits out a list of things to remember before starting exercise, and then very specific recommended actions based on your personal parameters, as in: how many additional carbs to ingest, and/or how much to reduce your bolus. It gives you these results based on Planned Exercise, and also Unplanned Exercise (when you can't adjust the insulin taken before exercising). Pretty cool!

There are also links to a pretty useful page on troubleshooting highs and lows with exercise, and a page that very concisely describes parameters that effect glucose variability -- great reminders!



According to ExCarbs, for a planned 30-minute walk around the block with my dog at a mild pace, if it's at least two hours after my last meal bolus, then I could expect to need an extra 15 grams of carb that would have to be consumed partly before, during and after my exercise. An alternative might be to try reducing my basal rate by 50% about an hour-and-a-half before my walk and for an hour afterward, though I could still need food on top of that.

YDMV and Exercise Effect may differ, so as always the site offers a catch-all waiver reminding users to: "Plan-Try-Review-Adjust."

I like it! This tool may not be exactly a crystal ball, but it certainly gives me a sense of what I might expect in an exercise session of certain length and intensity.

I also like how the ExCarbs site includes a number of general tips and tricks about exercise and diabetes. For example, under the "Adjusting Carbohydrate for Exercise" tab, they list an "Easy Approach (based on clinical research): Assume that muscles use glucose at a rate of 1 gram for every Kilogram (2.2 Lbs) a person weighs every hour. So for a 70 kg adult they will need to take 70 g of carbohydrate each hour (or 35 g every 30 minutes)."

Where else can you get this level of detailed information? And I like that it's all FREE and just a click away -- with nothing I have to buy or register for or subscribe to.

Kudos to Kerr -- and now Sansum -- for working on a practical resource like this for the insulin-dependent community!

The Bad

Then there are some tools that are marketed as a diabetes "exercise predictor," but really don't hit the mark, IMO.

For example, a recent email pitch about a new "Genetic Exercise Predictor" caught my eye, as it seemed like a more XRPredict+ LogoDNA-specific version of what I had seen above. This pitch for the XRPredict+ came from a UK clinical diabetes researcher named Ben Kelly, who works with British company XRGenomics.

At first I was captivated by how Kelly described this to us and others in the D-Community: it's a genetic DNA test that allows researchers to predict how certain types of exercise will affect PWDs (people with diabetes), before anyone steps foot near a bike or treadmill.

Turns out it's mail-order test kit that's actually been commercially available worldwide for about two years. It comes with a mouthswab, test tube for collecting your saliva sample, and return packaging -- similar to other DNA test kits on the market. It also comes at similar cost, in this case 149 Euros, or about $193.

The XRPredict+ site explains: "During the order-process you also fill in a short questionnaire that includes questions about your lifestyle, your height and weight, and your fitness goals. Once our analysis of your profile is complete, your 17-19 page tailored guidance report will be sent to you. The report will go in to detail about how you adjust your life-style to best tackle your personal fitness goals."

Hmm, this isn't really a "predictor" at all, is it? Certainly not of any immediate practical use for those of us trying to adjust insulin needs for daily exercise.

Really, you first have to send in a cheek swab DNA sample to their UK-based lab for analysis on a patented gene chip array that reads a particular exercise-specific SNPs (single nucleotide polymorphism), and then 1-3 weeks later (what?!) you get a loooong paper report mailed back to you with "suggestions on how to improve individualized targets." I just HAD to re-read their section on "Why Take the Test?"

The crux of the whole thing seems to be discovering where you fall on the high/low responder scale to cardiovascular training, which apparently appeals to some health-self-tracking enthusiasts. But the only real wisdom offered by this company is that "low-responders may have an 'excess' response in their muscles" and therefore may need to take more 'rest days' between exercise sessions -- whereas high responders "should be seeing a clear and measurable improvement in your aerobic fitness levels" and if not, they can "provide advice" on how you can up the intensity of your workouts.

Huh? I'm sure not seeing $193 worth of value here -- not even for people with type 2 working through issues with insulin resistance. So the test might say you respond more or less to cardio exercise? Either way, you still need to do it, and you can probably get better advice on how through a personal trainer.

And somehow I'm particularly skeptical given all the drama surrounding the home DNA testing offered by 23 and Me (they had to pull the product from market after the FDA objected to offering "uninterpreted raw genetic data" to consumers). I'm sure there must be some value buried in this XRPredict+ test, but it sure isn't in dealing with the immediate type 1 diabetes Exercise Effect.

The Unavailable, But in the Works

There's hope on the D-tech horizon, I'm happy to say.

Along with the rest of the Diabetes Community, we've been closely watching the many data innovation and data-hacking ventures that comprise the #WeAreNotWaiting movement.

One of those is a so-called Do-It-Yourself Pancreas System (DIYPS) being developed by tech-savvy advocates Dana Lewis and Scott Leibrand, whose system will offer "real-time predictive alerts for future high or low BG states... predicted based on CGM, IOB (insulin on board), and carb data input into the system" -- allowing us to make adjustments in advance. Now this is something that will REALLY help manage the Exercise Effect more effectively.

As Dana described it to me when I saw her at a summer conference, using the current prototype, she is already taking advantage of predictive alerts quite a bit in advance to going low, and the system's smartwatch-display will eventually advise the user how many carbs are needed, whether a temp basal setting on your pump might help, and more. She also tells me they've built a specific exercise-related feature called "activity mode," which changes the BG range you're correcting to -- instead of shooting for 100-120 for example, the two-hour activity mode setting would modify the range to 100-140 to allow for a safer margin for corrections and preventing lows. Awesome!

This sounds pretty cool to me, and I can't wait to see something like that replicated in devices we have or made more widely available for the rest of us!

(Oh and btw, CONGRATS to Dana & Scott on their engagement! Good technology breeds love...?)

Overall, it's great to know that these efforts being made to help us better manage exercise with insulin -- a need that's been sorely neglected in the past. Meanwhile, while we wait for an ever-better tool, it remains all about trial and error when it comes to the Exercise Effect!


Disclaimer: Content created by the Diabetes Mine team. For more details click here.


This content is created for Diabetes Mine, a consumer health blog focused on the diabetes community. The content is not medically reviewed and doesn't adhere to Healthline's editorial guidelines. For more information about Healthline's partnership with Diabetes Mine, please click here.