Bike to Work

I’ve been biking to work about 14 miles round trip for the past six years, and I was diagnosed T1d diagnosis just over a year ago at 38 yo (largely due to noticeable increase in effort while cycling, combined with weight loss). I am hoping someone here might be able to suggest some strategies for handling meals right before my morning commute.

While I have a good handle on exercise in general, the challenge with the bike commute is that I need to eat breakfast before leaving. For about a year after diagnosis, this didn’t appear to be a problem. I would eat breakfast around 6:30a, bolus (injection) at that time, and then bike to work at about 7:30. I never had a low on my way to work, but I also didn’t have a CGM.

I moved to a Dexcom G5 in January, and Tandem T:slim x2 in March. With the Dexcom, my BG was dropping considerably on my way to work–often with false lows, but other times I found I actually was getting fairly low (suggesting that I probably was in my 60s occasionally before I had a CGM).

My strategy now is the following: reduce basal 50% at 6:00a; eat breakfast around 7:00a (no bolus); bike at 7:30a; bolus at work at about 8:00a, and resume normal basal rate. This works in that my BG drops very little on the way to work. The downfall is that (a) I sometimes I arrive higher than I’d like (but not worrisome high); (b) I have to remember to bolus shortly after I arrive (I occasionally forget until I notice my BG rising); and © I get false occlusion alarms on the Tandem because of the temperature change from being outdoors to indoors. The lattermost is most frustrating, especially when it cannot determine how much insulin it gave during the bolus.

Does anyone have alternative strategies that might work?

hi @archaeoholic, first off - wow nice strategy. since it’s “almost” working my suggestion and opinion is to stick with it and add modifiers:

use the temporary basal rate, so the pump resumes normal basal after a specified time, this saves a step

you can either use a missed bolus reminder so the pump alarms when you don’t bolus for breakfast, or use a independent alarm on your phone or watch. on an iphone, you can alarm when you reach a location and you can repeat an alarm for the work days, or just on time, or whatever.

as far as the occlusion alarm, I am not convinced the occlusion alarm is from temperature and might even indicate a pressure sensor problem as well. if it is temperature related, I would just preposition the pump so that it is closer to your body perhaps under your shirt/bike pants. That should keep it closer to body temp for the ride. I actually have to do this when I am in harsh environments as well. cheers, keep up the great work!

hi archaeoholic, thanks for posting about your experience - it helps to hear of someone dealing with similar challenges. I was also diagnosed with T1 in my late 30’s (I’m 44 now) and have been using the Tslim and Dexcom G5 CGM for a couple of years now. One thing to consider is whether you are having the same amount of carbs for breakfast each morning - if you’re having less or more, consider changing the temp rate accordingly. I personally stop my basal rate entirely about a half hour before biking and keep it off until I stop biking because my basal rates are low and low BG events while biking can be dangerous. It feels safer to run a little high than to get into an accident due to a low. Have you read the Pumping Insulin book? I found it helpful for learning about managing insulin and exercise. I also found that I have to treat my experiences as experiments and see how I personally react.

I used to bike as one of my main forms of transportation, but I’ve changed to only occasionally do rides that are more than a few miles because I had a bad low while biking last fall. (I figured out afterwards that my glucometer strips had been damaged by the heat and were reading much higher than actual, so my CGM got off calibration. I learned the importance of keeping my glucometer strips in a gel pack when temperatures get over 80ish.) I now do my exercise more at the gym or pool where it feels safer if I have a low. I now check my BG with my glucometer before getting on my bike every time and then stop and prick my finger every 15-20 minutes since my BG can fall rapidly when I’m doing heavy exercise and I haven’t eaten enough carbs to account for it. I find that the CGM cannot keep up with rapid changes in BG since it is measuring the interstitial fluid and not the blood - I think it’s about 20 minutes behind. I’ve learned to focus on the trend in the CGM reading instead of the value and I set my alarms on the CGM alerts to be 2 mg/cL/min to help give me heads-up about quick changes. I have a hard time hearing the alarms when I’m biking, so I sometimes set my iPhone on full volume to give alarms as reminders to check my BG and turn the basal rate back to normal. I guess another option would be to change the volume in the CGM settings to be HypoRepeat (loudest) while biking to be more likely to hear it over traffic. Sometimes I intentionally wear a shirt with a chest pocket so I can keep my iPhone or pump closer to my ears, to make it easier to hear alarms.

I haven’t noticed a temperature change triggering an occlusion alarm. I agree they are annoying, especially when having to adjust the bolus if it happens during bolus delivery.

Thank you, Joe and AbeOakland. In regards to temporary basal rate, since I bike on a regular schedule, I use a programmed basal rate profile that automatically lowers at 6am and goes back to normal at 8am (and similar drop/increase for the afternoon ride home). I’ve found this works better than a temporary basal rate simply because I don’t have to remember to turn it on first thing in the morning (although I have to remember to switch on or the bike commute profile the night before, this is less challenging). I hadn’t considered using the bolus alarms, and I have that now set.

I got in the habit of eating the exact same number of carbs (~75g) for each meal when I was first diagnosed and was shooting. I like the flexibility that comes with the pump, but I’ve actually found that this is still the magic number.

I’ve definitely had problems with the CGM not keeping up with rapid changes, especially when carbing up before my ride home. Recently, I started using Vitalyte drink mix (largely powdered glucose) to carb up for my ride home. It’s great in that it acts quickly, but it seems to confuse the Dexcom when my numbers climb rapidly and then start dropping (often resulting in no trend arrow, and ultimately resulting in the ??? readout on a few occasions). In regards to the alarms–I got the Apple Watch solely for this reason–I can easily watch my numbers and the trends, and I get two sets of alarms.

Fortunately, I’ve only had one real low (48 mg/dl–the lowest I’ve ever gone thus far) during a bike ride, almost exactly a year ago before I fully understood how to handle exercise. I left my office in a rush and forgot to carb up. After that, I learned exactly how much I would drop in my 25-30 min ride home (about 100 mg/dl) and carbed up accordingly. That regular drop held constant for months; now my drop seems to be much more variable.

I’m 67 and have been T1D for 53 years. I find that when I am involved in vigorous exercise, I adjust my Tandem T-slim pump on a temporary rate, often times completely shutting off my pump until exercise is completed. I am an inexperienced rider but I will be riding in the JDRF Ride to Cure in La Crosse this August and am concerned with how I will manage with a potential 100 mile ride in summer heat and humidity. So far, shutting off my basal and monitoring my BG has worked well for training rides.

It sounds to me like you are handling it fairly well. I did a similar commute when I was in my 30’s. I did not have a pump at the time. I now have a minimed pump and sensor and I am really happy with the accuracy of the devices. Can you possibly switch to a different system? Also, there is no set way to manage sugar while exercising, you just have to keep trying to test and figure out which methods work best. Everybody responds differently! I usually reduce basal to 60% at the beginning of exercise and for 3 hours thereafter. I also sometimes bolus for fewer carbs than I’m actually eating, and I will adjust my eating patterns based on what my fasting BS is. If I wake up high, I eat after I exercise, etc. Good luck, and don’t give up. Biking is such a great way to commute to work, but one needs to have good control to be safe. Better to err on the side of caution and run a little high. It’ll come down later.