I am an avid racing-level cyclist. I currently use a pump and find that after 2 hours, no matter what, I always go low, unless I use zero basal. I finish races and rides with normal glycemia. I am wondering what evidence is there for or against this practice? What do you advise patients at this level of intensity to do, other than consume tons of calories (which I am sure you can appreciate is hard to do when riding)? Thanks for your time.

Patty Bonsignore


The first step to protect yourself from lows is to start your ride after a meal. This will ensure that you are starting your ride at a higher blood glucose level. Secondly, for your particular circumstance you may want to temporarily suspend the basal pump dose. At Joslin, in this type of situation when we recommend that the basal dose be suspended, we suggest doing this 1 hour prior to the start of the longer duration activity. You can keep the basal rate on the pump suspended for up to two hours, and we don’t usually recommend suspending it for longer than that. When turning the pump basal rate back on, make sure to turn it on at a lower dose than normal. This reduced basal rate is usually 40% less or more than your usual basal rate higher. As you experiment, you should seek advice from a diabetes pump specialist .

3 replies

type1skillset 2012-10-16 17:47:36 -0500 Report

Thanks for the great follow up she_sugar. I presumed that was what was meant (and even if it wasn't,it is what I do already). I was more after what evidence supports or does not support running zero basal rates in high intensity exercise. I know the risk when not exercising, but contracting muscles is the only other pathway for glucose transport so wondering if I can get away with it longer. What are your thoughts?? Do you know any evidence around this practice (exercise lasting longer than 3 hours however)?

She_Sugar 2012-10-16 08:05:12 -0500 Report

I also do exercise after a meal as suggested but what was neglected in the advice was to bolus less for your carbs or you won't be starting out with a higher glucose as suggested. Exercising when your insulin is peaking with a meal doesn't work for everyone either because this is the easiest time to go low if your adjustments are off.

She_Sugar 2012-10-16 08:02:03 -0500 Report

I would not personally consider turning off my basal rate during extended exercise. You will always need insulin during exercise. Every individual is different in their experience and it is an experiment of sorts to find what works best for you. Great blood sugars and no lows can be found through a lowered basal rate and by eating regularly. I have run marathons with not one low blood sugar- before the days of CGM's even. I love Shot Bloks by Cliff. They are a great blend of simple and complex carbs so they work to raise the blood sugar but also maintain it. They fit in the pocket easily and do a wonderful job. I often eat these kind of carbs with intense exercise every so often without bolusing for them and my sugars maintain beautifully. If you turn your pump down for too long or off you won't have a carrier for your food to reach your blood stream to use for energy and I find you battle with post exercise highs due to a lack of insulin on board. Congrats on trying to figure it out, the answer isn't cut and dry but keep asking for input and taking notes on your experiences.