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Running with T1D: Perfecting the Flat Line Run!

Updated: Dec 9, 2020

This is my first post in a series about running with t1d! I'm so excited to finally have this platform to make longer content that is useful to you all to live your best and fullest life with diabetes!!

DISCLAIMER: This is not medical advice, but simply my experience in finding an effective way to manage my blood sugar while running. Please work with your endocrinologist or doctor for medical advice!

There is so much I could write about this topic, but I’m going to try to keep this post short and straightforward because I believe that simplicity is key, especially when approaching something as complicated as running with t1d.

I wish I could give an easy answer, like, do these 2 things and you will have perfect sugars while running. It’s not that easy. However, I’ve logged a lot of miles over the years and have come to find that our body is more predictable than we often give it credit for, we just have to pay attention.

This is the method that I use to establish a t1d running routine to get that flat line during and after a run. I revisit these steps when I notice that my routine is no longer working (about every 6 months) or when I make a change in my care (like switching to pump from MDI).

This guide is broad and high-level so that runners of all levels (including novice!) can gain insight into their numbers. I'm always happy to answer comments/DMs about more specific questions :)

Training for a race? I suggest getting your t1d running routine down before you even begin training. As your body changes throughout the training, don’t be alarmed if you will have to change your routine a few times when mileage increases and as your body changes to adapt for more running.

Let's get into it, friends!

Step 1: Plan

Pick ONE run distance/ time for your test run. You’ll be doing this run a few times to find what works for you, so pick something short enough that you can do regularly but long enough that you can see trends. I usually pick 3 miles. If you’re new to running, maybe pick 30 minutes of a run/walk combination. Once you get that distance down you’ll be able to adjust based on longer or shorter runs.

Remember, keep it simple. The key is to not to introduce too many variables at once as you figure out what works best for your body. Otherwise, you’re unable to detect what actually works and what doesn’t.

Step 2: Aim High

Complete your first test run!

I think it’s easiest to start with slightly elevated sugars to prevent dangerous lows. For my test run, I start my blood sugar between 150 and 180, and run with NO insulin on board and preferably in the morning (or in a fasting state) to eliminate some of the variables. If you go low, treat it (and stop the test unless you feel comfortable continuing).

RECORD what you find out, including all the variables that were part of this run. This is the most important part!! (I have a template, if you want it email me ( or drop me a comment!)


  • The temperature outside

  • MDI or pump

  • The macronutrient profile of your diet and last few meals

  • Duration of run

  • Intensity of run

  • Inclines vs. flat roads

  • Time of day

  • Outdoor run vs. treadmill

  • The timing of your last meal vs. fasted

Step 3: Make ONE adjustment

This could be anything you feel is right for your body, but essentially you want to think about what you could add or take away from your previous test for a better result. Adjustment recommendations are below. Try to just make ONE adjustment at a time. Simplicity, ya? Here are some suggestions:


Trending up during the run? Consider:

  • Increasing basal rate by 30% one hour before you run or during your run

  • Giving yourself one unit of insulin before your run

Trending down during the run? Consider:

  • Eating a snack before and/or half-way through your run (I like gomacro bars!)

  • Decreasing basal rate one hour before or during your run with a temp basal

Dropping after the run? Consider:

  • Decreasing basal rate during run with a temp basal

  • Eating right after run

Rising after the run? Consider:

  • Giving yourself insulin right before the end of your run or right after finishing

  • Increasing basal rate during the run with a temp basal

  • A low-impact/ intensity cool down after the run to lower adrenaline/cortisol in system, like walking or yoga

Do your test run again, keeping as many variables as possible the same, but this time with your adjustment. For example, if last time you ran a loop around your neighborhood at 6am, do that same route again!

Record what happens! Did the adjustment work? If it didn’t work, try to determine if it was because a variable like temperature of time of day (which is why it’s helpful to write them down) or if you need to adjust the adjustment or chose another adjustment!

Step 4: Repeat!

Repeat step two over and over again until you get that flat line. The important part is to. keep recording what happens after each run so you can see what's working and what's not! I like to use the notes section in my phone so it’s always with me, but I also have a super fancy template that I can share (email me!).

I find I typically have 1-3 adjustments when I get to that flat line. Again, try not to overcomplicate things.

Step 5: Celebrate!

Once you’ve got your test distance down, celebrate yourself! Conquering a run is one thing, having great sugars adds another level of accomplishment for you to celebrate :)

Step 6: Repeat for Variables

Now that you’ve got one run distance down, you can start to trust your body and learn how different variables may play a role in your blood sugar. For example, if you did your original test run in the morning, you may want to try in the afternoon and see if there are any differences.

And because I know you'll ask...

Here is my current run routine! The biggest variable for me is run distances (I split up under 45 minutes and over 45 minutes):

Under 45 minutes: I reduce my basal insulin by 40% for the hour leading up to the run. I resume insulin with a 40% increase during the run.

Over 45 minutes: I reduce my basal insulin 75% for the hour leading up to the run, and during the run when there is 30 minutes remaining, I resume the normal basal. I also eat half of a go macro bar 15 minutes before the run, and the second half half way through! Long runs cause a lot more insulin sensitivity in my body!

Let me know how this works for you! And what other blogs about running (with t1d) would be helpful for you! :)

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