Physical activity and BG level

I want to get some feedback on a thing that I seem to deal with quite often.
There are really 2 scenarios that produce results/BG behaviors that I find confusing.

Some background: I’m a LADA type 1 and have been managing my BGs using a Medtronics 670G pump, continuous sensors and auto-mode for ~1 year. Before that I used a 530G pump without continuous sensors for 6 - 7 years. During this time period I’ve been able to keep my A1Cs in the low to mid 6 range most of the time with a few excursions into the low 7s.
I am very sensitive to insulin with an average daily usage of ~22 units with a carb intake in the 200 range.
I find I have to be careful about how much physical activity I engage in, especially after eating and the associated bolus of insulin, otherwise I risk a low that comes on very fast.

Now we come to what I’d like some feedback on:

  1. My usual morning routine is a cup of coffee after taking my BG and calibrating the sensor. Usually the morning BG will be in the 120 - 130 range and coffee pushes it up into the 150 range. I usually don’t bolus for this but instead let the pump auto-mode deal with it.
    This last Saturday I decided to move the remains of 2 trees we’d cut down off of our back yard. This took me ~1.5 hours of what I consider to be medium physical activity.
    Before starting my BG, as reported by the sensor, was just below 160, during the activity I periodically checked the pump assuming my BG would drop and I’d be forced to stop and have some food to compensate. In reality the opposite happened and my BG rose to 170 by the time I was done moving all the wood.
    I think key factors to keep in mind are I had not eaten any food or taken a bolus of insulin before the physical activity. I also did not set a temporary target or suspend insulin delivery, the pump had given me several micro boluses during the activity.

  2. Later the same day I again engaged in some physical activity, this time what I consider to be light. I cleaned a number of (probably 20) pine cones off my lawn and dug a small hole around a sprinkler system pipe that needs repair.
    This activity occurred ~1.5 hours after I’d eaten a lunch that contained 84 grams of carbs for which I bolused ~6.4 units of insulin.
    I don’t remember the BG level reported by the pump this time (forgot to look) but based on past history it was probably in the 150 - 160 range.
    This time my BGs crashed, I drank a box of apple juice after realizing my BGs had dropped to 70 and had a down arrow. Ultimately my BG hit 63 before rising to 130 due to the apple juice. Based on having eaten this exact same lunch and had the same bolus many times my BGs would’ve risen to ~190 - 200 and dropped to the 110 range by 5:00PM if I hadn’t engaged in the afternnon’s physical activity.

So, I’m wondering why the 2 significantly different reactions?
Did my BG not drop during my much heavier morning activity because I had very little insulin in my system?
** I did not check for ketones after this, I guess I probably should’ve.
Is there any link to the food I ate and the way my BGs reacted in the afternoon or was it simply because I now had insulin on board?
Is it possible my system is still making insulin and the food triggered it?
Is this a common behavior for a type 1 diabetic?


Just one more consideration. My blood glucose levels react very differently to anerobic vs aerobic exercise. I learned this over the years as I raced inline skate marathons all over the world. Without getting into % of heart rate in different zones and % of time in those zones an easy way to differentiate is to think of sweating or not sweating during exercise. If you sweat you are in or approaching an anerobic state and you will most likely find that your blood glucose curve will look very different from the time you enter into your “sweating stage” until several hours, if not even days after you complete that exercise. If you exercise in an aerobic “non sweating” state you will find a much milder curve that will also last a lot shorter duration.

There are always exceptions, of course, and different people react differently especially trained athletes vs that individuals tend not to have a specific exercise routine.

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I’ve never equated anaerobic with sweating.

if sweating meant u are anaerobic, just think of all the folks doing anerobic exercise in Phoenix…

So a good portion of this bolus was peaking while you started activity. If your meal included protein, fats, with the carbs, it would slow down BG rise due to meal. So even the low intensity activity can cause low bg.

It is just a quick easy, non technical, way to evaluate if you are in or approaching anerobic state. There are always exceptions, just like there are a lot of people exercising in A/C in Phoenix as well as outdoors. I have competed in 100 degrees F as well as 40 degrees F in Northern climates and have sweat in both.

I’ve sweated plenty without being anywhere near anaerobic and I’d say the rest of the world’s population can say the same thing.

Exactly. Even taking out the garbage can drop one’s bg’s.

Yes, especially low intensity activity can cause low BG. I can raise my BG 20-25 points quickly going high intensity on a treadmill, for example, while taking that same amount of time in low intensity drops BG.

I would say the exercise I did was anaerobic, although I did sweat while moving the wood my heart rate didn’t rise to a level equivalent to running, swimming or skating.

EDIT: I think I misunderstood the sweating vs non-sweating reference (not sure I even agree with it as I’ve done both types of exercise, anaerobic - “weight lifting” and aerobic - “running”, and sweated during both so the analogy doesn’t seem to fit.) This activity was definitely anaerobic though, lots of weight lifted and moved vs just raising the heart rate by running or swimming or something like that. I know it’s more complex than that so let’s not fixate on that aspect of this.

Good point, I hadn’t thought about the timing of my afternoon activity in relation to the bolus. The meal did contain a good amount of protein and fat along with the carbs so I guess that explains why the low came on so fast even though the activity was minimal.

I’m actually more curious about why my BGs didn’t drop due to the relatively strenuous activity of moving the wood. I expected to have to correct for a low just like I did in the afternoon.

Can you check pump history? Maybe 670 suspended basal during the morning or afternoon activity. But suspending can’t undo or slow down large bolus already taken, and may be minimal impact if your basal is low.

Also, the more strenuous morning activity can have an extended effect resulting in more sensitivity to the meal bolus.

In auto mode the pump doesn’t use continuous basal, it uses micro-boluses when its algorithm determines I need them. The micro-boluses are either .05 or .025 units in size, at least that’s the sizes I see reported by my pump, other people’s may be different.

I can’t pull up that specific history on the pump, I need to download it to see it but I know the pump issued several micro-boluses during the morning activity and none during the afternoon.

Again, just to be 100% clear, in auto mode there is no basal delivery like there is in a traditional pump configuration.


I’m LADA as well. As of May 15th it’s been one year. I too am very sensitive to insulin so I’m MDI, no pump. I work out with another T1 and she suspends her pump during certain activities. The general rule of thumb for the majority of T1s seem that cardio like activities drop BG’s and weight lifting tend to raise BGs. I usually have to treat a low after a 20 min run. I would start out around 120-140. I keep tight control and eat 50g of carbs per day. I do my best to not go over that. I am finding that walking excessively drops me the most. Seems so strange! I was walking in Central Park (6miles logged for the day) slowly w kids, etc… and I had to correct w glucose tabs and juice 3 times. What I’ve learned from some of the amazing people on here is that everyone is different. So you have to keep taking note of what :arrow_up::arrow_down: You.

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Yes, I think managing BGs for exercise is more doable with a pump and is one of the prime reasons I switched from MDI. I, too, frequently suspend during exercise. Walking for long durations is a great activity and can definitely drop your BGs dramatically. With a pump you could easily reduce your basal to account for the extra, long-duration of exercise to prevent the lows, with experience, of course, once you learn how much activity causes lows! You might want to test out pump and CGM to see if it makes managing your BGs a bit more easy. Good luck.


My blood sugar reacts differently to aerobic exercise depending on my blood sugar level when I begin my workout. If my blood sugar is +/- 120 or above, running is very strenuous and my blood sugar tends to rise. If I start a run below +/- 120, it’s less strenuous and by blood sugar drops; slowly while I’m running and quickly when I stop. Any thoughts on why this is happening?

The time of day makes a difference too. I find dawn phenomenon really doesn’t end till about 11am for me. From the moment I get out of bed my blood sugar starts rising unless I take insulin, and physical activity, like coffee, can actually accelerate this rise, even though the same activity would drop me low later in the day. I tried going for a run every morning a while back and found I had to bolus for the run or would go sky high. Normally running will drop me low quickly however. Dawn phenomenon is powerful stuff!


I think the key to your post is “strenuous” rather than your BG level. (All things being equal). Let’s define strenuous as putting an extra strain on the body which it is not accustomed to, If I do a new activity, let’s say walk 20 minutes on a treadmill at 3.5 mph, it will put strain on my body and BG will increase during that activity and then come back down when finished. If I do that activity twice a day, after a few days my body will start to adapt to that exercise and BG will no longer rise, but stay stable and if I continue for several more days and that exercise becomes routine, my BG will actually drop during exercise. That is why for me light aerobic exercise such as a casual skate or walk will drop BG VS a strenuous exercise which will raise BG during exercise to fall afterwards. (please don’t somebody come back to me and tell me to repeat that exercise at 14mph on treadmill which is beyond my capabilities and my body would never adapt).

You also did not mention your normal BG. Same goes for Hypoglycemia. If your normal BG is 120, then when you drop to 80 you tend to feel hypoglycemic. If your normal BG is 95, then 80 feels totally normal. That is similar to what happens with exercise, so depends if 120 is normal or not normal for you.

There is also an element of body temperature. When my body temperature rises, BG will also rise. I have a very low BMI of 18.5 so very susceptible to any variations. I love to take 15 minute very hot showers and during that time my BG rises about 20 points. Then as my body cools over a period of about 15 minutes BG comes back down to normal. Body heat also plays a role in exercise depending on how strenuous the exercise and ambient temperature.

Lastly, you did not say how you measure BG. There is a lag time between BG from CGM interstitial fluid and finger stick from blood. If you initially did a finger stick and then are following up on your CGM, you will also find there can be a 25%-35% difference until one catches up with the other.

Not sure if any of this helps but just an insight into tests I have run on my own body.

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I don’t know what I would do without exercise. I try to ride my exercise bike every morning starting about 1-1/2 hrs. after breakfast. I put the bike at a resistance of 5 and try to get my heart rate up to 130 which is not bad for a petite 68 yr old. I can’t stay up there more than a few minutes then I slow down a bit. I ride 7 miles. Today I am starting at a 150 glucose level and will be down to close to 70 give or take when I am done. My glucose level never rises when exercising. If my glucose level was over 200 when I began then it might rise
I don’t know. If I have a day when I don’t exercise I have to give 2 units more at breakfast.

Great regimen.

Thanks for your insight! Very useful.

In my case the ‘strenuous’ is a consequence of the starting blood sugar, not the level of exercise. My run length and duration are very stable day to day. The variable is starting blood sugar. I really labor to get through it if I start above 120. I’ve seen it both with my CGM (today) and with finger sticks before that (only had the starting and ending BG data for the latter). I haven’t really considered body temperature so I’ll try to take more notice of that and see if it correlates.

One strategy I use is anaerobic exercise (walking) to drop my BG below 120 before I run. Unfortunately more often than not I don’t have the extra time for that.

If you go to your clarity reports how close % wise is 120 to your average glucose for past 14 days? Standard deviation for 14 days? What is your approximate starting range before run high and low over 14 day period?