Basics of Exercise with Diabetes: Going Low
When we exercise, heart rate goes up and muscles start to contract. And that’s at the most basic level. Additionally, complex signaling mechanisms increase our insulin sensitivity and increase the ability of our muscles to take up glucose without insulin through GLUT4 receptors.
Studies have shown this even happens during light stretching. Normally, our bodies can shut off insulin production and crank up our counterregulatory hormones (CRHs: any of the hormones that oppose the effects of insulin) to avoid hypoglycemia during exercise.
But for people with diabetes on insulin, we are stuck with the insulin-on-board (IOB -- the amount of fast-acting insulin that’s still active in the system) we’ve got. That IOB also suppresses those CRHs! And means we will almost inevitably go low if we exercise with IOB.
One study found that people with type 1 diabetes needed anywhere from a 50-90% reduction in insulin to avoid lows during exercise.
Basics of Exercise with Diabetes: Going High
Many people think that exercising with diabetes always and only translates to going low. But sometimes (often, even!) we spike during exercise, too.
This happens especially during anaerobic exercise. Blood sugars actually increase due to CRHs (like epinephrine & glucagon), which increase in response to anaerobic exercise. This response can be exacerbated if you don’t have enough insulin in your system (IOB) because insulin inhibits the production/action of these CRHs. Without it, they can run amok.
But again, if there is too much insulin in the system, it will inhibit the CRHs. Coupled with the increased insulin sensitivity of exercise, low blood sugar will occur.
Then, there’s the infamous post-exercise spike. This happens when the lactic acid that built up in your muscles during exercise gets sent back to the liver, which converts it into glucose. Once converted to glucose, it’s dumped back into the bloodstream so that the glucose can be stored back in your muscles for later exercise.
This is great! And normal and natural. Think the age-old fight-or-flight response: your body is simply making sure you’re prepped and ready for the next round.
But the blood sugar dump can lead to some super high blood sugars after exercise, especially if you have little IOB to counter it. For short runs (3-6 miles), I personally exercise with almost no insulin-on-board, so I bolus at the end of my runs to combat the spike.
It All Comes Down to You and Your Body
It’s super important to note that this is the science of what’s happening in the body during exercise. But the range of individual results we see is influenced by our current blood sugars, IOB, insulin management, diet from days prior, sleep levels, and even our baseline level of fitness!
I’m not saying you’ll always see these types of blood sugars, but this is always how the science is working behind the scenes.