Help debug my running

Pre-T1 I was a fairly serious runner. I ran 20+ miles a week usually and raced competitively for my age. Post-T1, well, that’s a different story.

My basics: 49M, diagnosed T1 last year, on MDI. Take 2u of Tresiba in the morning and bolus with Humalog as needed. Still in honeymoon phase; my C-peptide is about 0.9. Last A1C was 5.0. My target range is 75-115, and I stay in there most of the time.

At the moment I’m running in the evenings because there are a lot of complications with the mornings for me, having to do with insulin resistance and a big foot-on-the-floor rise. In the mornings, my problem is getting stuck high. For now let’s focus on the problem of evening lows.

Normally I try to start a run at around 130bg. Because I’m on Tresiba, I can’t turn my basal off. I wait at least 4 hrs since my last bolus so I shouldn’t have any other insulin active. The problem is that by mile 3 I’ve already crashed down to 70 or below. And I’m not running too aggressively here: pace is lazy, between 8:00 and 8:30. (I would consider 8:00 a normal pace, 7:30-7:45 a speed training pace, and 7:10 a race pace.)

An example from today. Lunch was 11:49am, 3.5u bolus. Got ready to run at 4:40pm. I had Gu blocks and glucose tabs before starting and was at 137bg. All these are meter values, Dexcom G6 is beyond worthless while running for me. At mile 2 I felt a little low so I checked: 76bg. Had 8g of glucose tabs, waited 5 minutes or so, and set off again. When I got home at mile 3 I was 48bg. Had another glucose tab and waited 10 minutes, when I was finally up to 65bg. I had a post-run spike up to 104bg about 20 mins after that, at which point I injected and ate dinner.

So clearly that isn’t satisfactory. I could start at a higher bg, but my understanding is at 150 or so that works against you, not for you. That leaves fueling more and earlier on the run. Best options for this? I carry glucose tabs, Gu, and gel blocks. Other possibilities I haven’t thought of here?

Any advice welcome. If we get this dialed in, we can start working on those mornings…


I use a variety of different carbs sources, depending on the circumstances and what I need.

You mentioned taking 8g of glucose tabs. You were 76 at mile 2, but consider that you had dropped from 137 at start. That’s a 61 point drop in 2 miles.

That is not 8g territory, that’s take-something-to-pull-your-butt-out-of-the-ditch territory.

  • Transcend gels are 15 grams of glucose. Very fast.
  • Huma gels are 20-25 grams (depending on the flavor). They are fairly fast.
  • Untapped energy gels are 25 grams. They are a little slower than Huma gels, but a little more sustainable.
  • Cliff bars are about 40-ish grams, but about 1/2 sugar grams and 1/2 slower carbs. Slower but longer lasting than the ones listed above.

The list goes on and on for what you can take. Glucose tabs are fine if you like them, but with drops like that, I think you need a little more.

Dropping in the first few miles is fairly typical for moderate level exercise. The glucose in your blood is the most readily available fuel source, so it’s the first thing your body will grab when you start.

You don’t need to run your BG higher. Just take sufficient carbs at the beginning, and in the first few miles.

It isn’t just the number, it’s the speed of the drop. The key thing to focus on is to try to predict where you will be in 10 minutes.

And yes, with Tresiba your hands are tied as far as adjusting your basal. The only thing you can do is fuel the basal sufficiently.


I agree with Eric. More carbs, earlier. I recently went back to MDI for a couple weeks and was amazed how much more I needed to eat during exercise. On a pump I can get away with 15ish grams carb/hour, less first thing in the AM. When taking lantus I needed more like 30/hour sometimes 45. Target your desired pre-exercise BG, then take carbs at the start, then intermittently as needed. Be prepared to bolus when you end. Those carbs have a tail and keep working after you slow down. I’d rather be 180 after working out than 50 mid workout, ymmv.


Thanks much @Eric and @Karl.n for the thoughts. I figured I’d need to fuel more during the workout, I just hadn’t guessed it would be this much more, especially with my incredibly low basal dose. Maybe exercise gets my residual pancreas working as well.

It sounds like starting in the 130s and having at least 15g during the workout for a 3mi run would be a good starting point. I could take 1 Transcend at mile 1; by then I should be down to ~100, but if it takes more than 8 minutes to kick in I’ll already be at 70 and falling. It might be better to take it right at the start despite already being in the 130s. That way the burn-off and the ramp-up will (ideally!) cancel each other out. I’ll try the latter out and see how it goes. Depends in part on how well I digest during exercise.

I’ve had post-run spikes that were due to over-carbing during a run and also to general post-exercise stress, but they’re unpredictable. I normally run a little before dinner time, which makes dosing and snacking a little tricky. With a big meal coming an hour or so later I don’t always want to give myself a lot of insulin or eat too much. That’s something else I need to work on after I get the run itself down.

Of course I want to get back to real distances as well. @Eric would you expect the carb needs to drop off as the run gets longer and I shift to using other energy sources?

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As with all things, you just gotta try it and see. You could always just slide the time depending on circumstances.

Right at start, 5 minutes, 10 minutes, whenever. Time is totally granular.

In general yes. And for you this will work to some degree. Your longer distances will be at a slower pace, so lipids are a little more of a fuel source.

But…. in non-D’s and for those using a pump, basal insulin is reduced for longer times during longer distances. This helps.

But with Tresiba, your basal stays constant no matter how long you go. And for that reason, you will always have to feed the basal some amount.


Yes! do that. Unless you’re actively going up, you need that buffer for digestion. The value of a CGM is to know directionality in addition to the raw number, if you prefer the meter for that.


Trial run 2

Started at 5:36pm at 133bg. Took a Transcend (15g) right before stepping out the door and moving.

At mile 2 (5:59pm) was at 64bg. I had been running a little faster than before (7:30 pace) because it was beautiful out and I wasn’t keeping close track. I knew I had 15g of carbs in me but clearly they hadn’t kicked in after 15 minutes. So I took 16g more of Clif Gu blocks, waited 15 minutes, and retested at 103.

At mile 3 (6:26pm) was at 91, so some of those carbs finally worked. Decided to add .75mi more, and ended at 98. Predictably I bounced up to 122 and then 136 about a half hour after finishing, so I injected and ate dinner.

Observations: I don’t digest quickly while I’m in motion, even “fast” carbs like Transcend. I had eaten lunch at 12:55pm so I doubt my stomach had much in it. I think I may need to push the Transcend back 5 minutes before I start, which unfortunately means waiting while I’m hanging out in the 130s. Not a fan of doing that, but maybe it’ll help it kick in. Further thoughts welcome!


@needlesandmath Really appreciate you posting your running debugging. It is so helpful to others that aren’t willing to post. Thank you and Keep Running!


A few notes on this.

You started with a BG of 133. But keep in mind, not all 133’s are the same! Was it a flat 133, a rising 133, or a dropping 133.

So always observe which direction your BG is going, and how quickly. Because that makes a lot of difference.

A few notes on this. (You are a doctor, so you probably have already learned all of this. :grinning:)

During exercise, blood is diverted from the digestive tract to the active muscles, which slows down the digestion.

Osmolality is a measurement of the concentration of a fluid, in terms of the number of solutes per volume of fluid. The osmolality of the blood and body fluids is approximately 290 mOsmol/L.

A hypotonic solution is any solution that has a lower pressure than another solution.

Hypertonic solutions have an osmolality higher than the body (> 300 mOsmol/l)

Hypotonic solutions have an osmolality lower than the body (< 280 mOsmol/l) which actively promotes fluid absorption.

Isotonic solutions have an osmolality similar to the body (= 290 mOsmol/l)

Tonicity is the ability of an extracellular solution to make water move in or out of a cell by osmosis. This determines what direction fluids flow across the membrane. Water wants to flow from areas of low concentration to high concentration. Your body wants to keep things equal.

Gels and solids do not digest as fast as liquids. Your body needs fluids to process things. If you don’t have enough fluids, the delay will be even more. The closer the carbs are to being the same osmolality as your body’s fluids (about 290 mosm/kg), the faster it will be processed.

Any gels you eat are thicker. They have a higher osmolality than your body’s fluids. So they take longer.

Fluids are faster, but they are harder to carry.

All of this is to say - making sure you take enough water with the Transcends will also help!


Thanks @Eric for the notes! The G6 sensor I am wearing never got around to even registering me at 133, or 64 for that matter. It’s lagging quite badly so I don’t have a good idea of whether that was rising or falling. I think it had me between 110 and 87 on the run. Maybe the next one I put on will be more useful.

Good review on tonicity. I drank what I thought was plenty of water before and while taking the Transcends, as well as while on the run, but I can try extra hydration next time. There are also powdered carb solutions I could mix with water and carry along, though I haven’t experimented with them yet.


@needlesandmath, those numbers are really good though!

I know the 64 probably spooked you, but it might have been bottoming out there since you then went to 103. And if that was the case, overall the low was not a big problem.

A flat 64 is really not bad. Not sure if you feel bad there, but again, it depends. A flat 64, a rising 64, a slowly falling 64, or a plummeting 64 - all of them can feel different.


strong text[quote=“Eric, post:9, topic:13694”]
Gels and solids do not digest as fast as liquids. Your body needs fluids to process things.

In my personal experience, glucose tablets work faster if I drink some water after chewing and swallowing the tab. I found this out by accident, intending to wash the sugar out of my mouth.

My fast liquid treatment for hypos is my own brew. I use the Karo Lite No HFCS corn syrup which is close to 100% glucose. I use a 5 oz plastic flask. One oz of syrup diluted to 5 oz give 6g per oz. 1 1/2 oz gives 8g per oz. I add a bit of electrolytes and use strong black coffee for the dilutant. Water or some other non-caloric liquid could be used.

I am retired on a fixed income. This is relatively inexpensive compared to gel, blocks, bars and such, besides being able to better control the amount of glucose grams I am taking in.

As to MDI using Lantus and exercise - I found splitting the dose 2/3 at bedtime and 1/3 in the morning. This helped to prevent nocturnal lows. If I was going to do a bike ride in the morning, I would delay the morning Lantus until after the ride. This may be a helpful plan for @needlesandmath Like finding out drinking water after eating glucose tabs causes faster BG rise, splitting the Lantus dose was because of nocturnal lows 6 hours after the dose. CGMs tout no more finger sticks and Lantus claims to be flat over 24 hours - well not in my experience for both.

Once again I find myself pushing a book by Sheri Colburg PhD, at type 1 diabetic, “The Athletes Guide to Diabetes.” I gave my copy to a nurse working towards CDE and just this week downloaded as a Kindle book. This one is revised from the one I gave away. The following is from the beginning of the forward by Matthew Corcoran MD - founder and president of Diabetes Training Camp Foundation.

“Make no mistake about it: diabetes is a complex, chronic disease that is more complicated than most. Exercise and sport involve complicated physiological processes and doing them with a disease like diabetes makes them that much more challenging to manage. This reality should not stop you from exercising, getting fit, or competing at whatever level you choose. In fact, as Dr. Sheri Colberg has written, diabetes should be your reason to exercise. The tremendous array of health and mental benefits that exercise and fitness bestow on you usually outweighs the risks, but you need to tackle the challenges with an understanding of what is going on in your body.”

— The Athlete’s Guide to Diabetes by Sheri R. Colberg


I understand the frustration with inaccuracy of the absolute CGM number. What directionality was it registering when your meter read 133? Up, down or flat? Or was it stochastic (random)?


Heres a trick I’ve been using lately for my own workout fast carb shot when I’m struggling with lows.

Mix 15g Gatorade powder (dextrose) with 20-40g table sugar (sucrose). Dissolve in ~1/4 cup warm water. The mixture ends up being ideal ~1.5:1 glucose to fructose and doesn’t need to be washed down like a gel. Its cheap and stable in the fridge for at least a day or two (never wanted to push it).The osmolarity isn’t ideal, would be better with 20 oz water, but for me it serves as an emergency backup and I usually have separate bottles with water or more dilute sports drink.

I got the idea from Alex Harrison


The liquid mixes are generally faster, but the challenge with running is carrying the volume of liquids.

There is a limit to how much liquid you can easily carry. If your bottle is filled with carb liquids, then you can’t hydrate much because you can only drink when you are low!

For cycling, you can more easily mount a few bottles on your bike.

Gels are smaller, so that’s why I’ve recommended them for running.

A few gels, and also your preferred hydration, gives flexibility to either take carbs and water or just the water.

But like all of this, it just takes testing different things and seeing what is best.

Fast, light, small, easy to carry - there is always a trade-off.


@Eric I was surprised at the 64 to be honest, since I felt terrific. My guess was in the 90s. Pace wasn’t slackening at all, which is my first sign that I’m crashing. I suspect that I was flat or already rising. I was being conservative in having more carbs. Next time I’ll hydrate a little more with the pre-run Transcend and wait a minute before starting out.

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@Karl.n Right, sometimes I can get velocity information that’s accurate even if the numbers aren’t. It registered a flat rise and a flat fall (i.e., no angled arrows at all). Which is odd since this morning’s English muffin caused a brief angled rise. Why glucose tablets in the afternoon don’t do that is a mystery, especially since I was certainly better hydrated than in the morning.

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Sometimes when I am riding, especially when it is very warm, Dexcom may show my BG (actually interstitial fluid glucose level) low in the 60s. I will feel strong without any hypo symptoms. On occasion I will stop and do a finger stick and BG will be in the 90s. As I have said before I put this discrepancy down to perspiration depleting the interstitial fluids causing a false low reading.

Now, I have had a few where Dexcom is reading in the 60s and my performance is dropping. On those occasions a finger stick will show it to be correct and I need to treat.

CGMs have limitations and we can’t give them our complete trust. We need to be aware of how our bodies are responding to those numbers.

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Thanks for the recipe @CarlosLuis – sounds like it’s got a real kick. Agreed that paying for all of the custom carbs isn’t a lot of fun.

Your tips on basal dosing make sense for Lantus, but Tresiba is usually single-dose. It’s got an extra long time of action (36-48 hours). Also since I’m on only 2u, splitting wouldn’t make much difference either way. Pumping will eventually make this easier…

I have a copy of the Colburg book! It’s got some good tips. Hers and Scheiner’s were the first two reads I picked up post-diagnosis.

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Wow, 2 units for 24 hours = 0.08u per hour. Tandem has a minimum of 0.1u per hour. Now if you are running C-IQ the pump can go lower if needed. What is your total daily dose. I have a higher basal to bolus rate than the 50/50 that many are close to, more like 65 basal:35 bolus for a TDD of around 26u.