Very Bad Low BG 1 day after ride?

Hi All -
I posted this in the sports group the other days…

My wife and I have been getting into bicycling a lot.
This past weekend we did a ride on Sunday morning at 10:30 am.
It was a nice ride, lots of hills and I did not make the whole ride.

Then did not eat lunch until about 2:30 pm after spending $$ and too much time in bike shop.

We went home, had a late lunch and a shower. Dinner was 2 slices of pizza and a beer.

All was good from a BG perspective. I have been a type 1 diabetic on a pump for a long time (pump 15 years, Type 1 for 43 years).

Monday, I helped my mother just out of the hospital after surgery. Missed a normal lunch and about 1:30 pm had a sudden BG crash. To the point where we needed EMTs and after the pushed 25 cc of glucose into my veins, I came back to life after about 40 minutes. Bad! Bad! Low in my book.

So what is going on? I have lost ~15 lbs since Feb. I have been bicycling ~1-2 per week, ~1-2 hours per time. This is the third serious low. My wife and I are quite concerned. What is going on?

Theories are:
1- Drug interaction with statin I started taking
2 - Due to weight loss, basals are wrong
3 - Delayed Post Exercise Hypoglycemia

#3 is the best hypothesis, but these lows happen very fast. I also can’t seem to detect them. Also I become belligerent and refuse glucose (2/3 of these lows). It seems like some of these occur ~24 hours after the exercise. The idea is that the depleted glycogen stores trigger a rapid drop in BG.

The question for the group is -
Anyone else see these kinds of lows?
What do you do to avoid this?


Look into a CGM. That should help. I would look into #2 though. My basals change every few months based on regular exercise. I’ve got a MiniMed Realtime CGM, and see my fasting/resting/betweener glucoses are normally lower for at least a few hours after doing some good exercise, sometimes for a day or two.


I ride 3-4 times per week, mostly in the woods. We usually ride for 2-3 hours per ride, with two of my weekly rides being after work rides.

I have had Type I diabetes for 23 years.

Because of my late after work rides, I was experiencing extreme lows during the night (20s-40s). I spoke to my doctor, and he recommended adjusting my novalog dose for dinner on those nights by cutting it in HALF! I have been doing this ever since with a lot lower number of lows at night, and with normal blood glucose readings in the morning (80s-100s).

I’m not sure if this information helps since you are using a pump. I just wanted to let you know how much riding can affect your blood sugar in relation to insulin dosage.

One other point is that I too experience delayed lows from exercise. Sometimes I have difficulties keeping up for an entire day after a good ride.

Cutting way back on my novalog after a ride made the biggest difference for me.

Good luck!


P.S. I am currently in the process of getting a Dexcom 7 Plus CGM that will hopefully make a big difference with these concerns.

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Pretty much learned the same thing you did. What I wind up doing is to suspend insulin delivery from my pump starting about 1/2 hour prior to my ride. While on the bike I eat like I used to before I was diagnosed. Also I TEST every 30 minutes. The testing was a royal piin…could not get into a rythem, made for hard rides. I got a CGMS. It it the best thing for the bike. When I am done with my ride, I start my basal rates up again, but not at 100%. I go with 50% for an hour, 70% for an hour, 85% for an hour and then back to 100%. I found that if I went to 100% right away, I’d be low in 25 - 30 minutes. Remember that the effect exercise has on your BG continues fro several hours after you stop.
It appears to be that when it comes to exercise & insulin, you need to experiment to see what works best for you.

Keep on going & good luck

Dude! You are one lucky bike rider! You nailed it on #3! In the words of my endo, exercise makes your insulin work more “efficiently”. What is unfortunate is that no one in the world of medicine quite understands why… Glycogen depletion and replacement is not a short term event, meaning it can take as long as 48 hours after a strenuous ride to get your muscles back to their “comfort level” of stored glycogen. A friend owns a triathlon shop in north Florida and works with a group of Type 1 teenagers. Their insulin dosage has been reduced by half in the past year, and these kids are tearing up the amateur triathlete circuit!

Glycogen comes from the glucose in your blood, and insulin is the “catalyst” in the conversion from glucose to glycogen. Remember, two things cause low glucose events: The first is not eating right. The second is taking too much insulin. The balance between exercise, food intake and insulin dosage can get pretty tricky. My own personal solution was to watch what I eat, take a Power Bar, a test kit and my cell phone with me on my bike rides, and go out an hammer!

I don’t wear a pump, but my riding buddies that are also diabetic and wear one take theirs off before the ride. None of the pumps on the market have “closed the loop” between glucose levels and insulin dosage, so you are left with having to figure this one out on your own. Remember, exercise will reduce your body’s need for insulin. And taking a break from exercise will increase your need for insulin.

Listen to your body, carry a test kit, then pull your head down low over the handle bars and go out and hammer!

Hang in there…


Hi Folks -

Thanks for all the comments.

I have a CGM. I wasn’t wearing it that often because on rides I sweat a lot and it was always coming unstuck.
At $35/sensor (not covered by my health insurance) I was some what reluctant to flush $$$.

I do carry a test kit when I ride and I test every 30 minutes or so. I have done a few rides since the post and your suggestions are great

I have now made a few changes with my Endo:

1- Basals - On the Minimed pump I now have three basal patterns - Pattern A - Riding (50%) if normal basal), Pattern B - Post-Ride (~80%) and Standard. I obviously use Pattern A during the ride, Pattern B for up to 24 hours post ride, and Standard other times.

2- Eating post ride - I now eat a lot more protein post ride. This shunts all the post ride carbs straight into glycogen replenishment (so the research says).

3 - CGMS - I switched to using mastisol and opsite flexifix. Sensor says on much better (at least 2 sensors after posting with ~150 miles of riding).

Still riding hard.
Aside from fun, I am also trying to dump some more weight. I am down ~12 lbs. I’d love to lose ~15 more.


I am ususally very aware of going low accept when riding. For this reason I bring my meter and check myself about every 15 miles or around an hour. I also usually bulk up on carbo’s a bit before a ride to - starting at around 200. It may sound silly but I take a PBMJ with me for every hour so that I ride. There are alot strange dynamics going on with your body if you ride alot - I am a normally a 60-70 unit a day guy combination of Lantus and Humalog. Many times on a week to 2 week tour I take almost 0 lantus and 20 units of Lantus and I am still a touch low - so my insulin needs go down by 2/3rds. I about to start on pumping and it’s a ongoinging discussion with my medical team on the temp basel for riding. We are going to start at -50% and then adjust. You have also noticed you can get a delayed effect or elongated decrease in insulin needs hours and days after riding - personally I find this quite common. Just something to be aware off.

Mike and Frank,

I would agree that #2 is a factor, but my own experience indicates it is a little more complicated than just weight loss. While you are losing weight, your cardiovascular conditioning is also improving. Both will affect basal dosages. On top of that, insulin works “more efficiently” during exercise. Nobody knows why.

So, while losing weight appears to be a significant factor, cardio conditioning also makes a difference. Adding the glucose to glycogen conversion on a routine basis also affects your basals. In short, its complicated, but it works!

Get out there and hammer!


Can’t say much about #1. #2 and #3 both sound right. I reduce my basal to 50% about an hour before my rides (assuming I’m not high already) and keep it there until I’m finished riding. I also fuel along the way at least 15 carbs/hr. I check BGs about every 30 minutes while riding.

For long rides (centuries), I wear my CGMS and I also check with my meter frequently. Using the above strategy, my BG is usually always good during the ride. My challenge is what happens after the long rides. Sometimes I would go really high just after the rides and I always have to be aware of #3. I’ve started bolusing at the end of my rides and/or ending my temp basal just before finishing. I rode from Seattle to Portland this weekend (202 miles). No problems with the plan I described.

The trick is to find out what works for you. It’s trial and error.