Blood Sugar Control — During and After Exercise

1/30/17
WRITTEN BY: Christel Oerum
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Medical disclaimer: No adjustments to care should be done without consulting your medical team. If you are new to exercise, haven’t exercised in a while and/or haven’t seen your medical team in the last 3 months, it is advised to do so before engaging in any kind of physical activities.


Blood Sugar Control — During and After Exercise

Exercising with diabetes can be tricky because you never know exactly how your blood sugar will react. However, there are some general rules that apply to all of us and when you know those rules, it becomes easier to recognize patterns, find your personal “formula” for food and insulin, and exercise with fewer blood sugar headaches.

In this article, I’ll walk you through three different types of exercise, and what you usually can expect from a blood sugar perspective. I also suggest strategies for managing your blood sugar during and after each type of exercise.

Types of exercise

  • Steady-state cardio
  • Interval training
  • Resistance training

Blood sugar management during and after steady state cardio

The general rule for steady-state cardio (where your heart rate stays moderately elevated for the duration of your workout) is that it will make your blood sugar decrease if you have any insulin on board (IOB). Some people don’t start to see the effect until 20 minutes into a workout, and some will only see the effect during specific types of workouts.

What happens during steady-state cardio is that you increase the body’s use of blood glucose. So, if you have high levels of IOB during your cardio session, the muscles will take up more blood glucose and the risk of low blood sugar increases. This risk is not only increased during the cardio session, but also up to 48 hours after you’re done.

Strategies for preventing low blood sugar during and after steady-state cardio

  • Reduce the amount of IOB (basal and bolus) by adjusting your insulin
  • Do your cardio fasting, or at least 4 hours after your last bolus
  • If exercising for longer than 60 minutes, consider a carbohydrate and protein snack
  • Consider adjusting basal insulin for up to 48 hours after a cardio session

For more information, you can read a detailed hour-by-hour description of how to manage insulin and food around cardio workouts in the post How to Prevent Low Blood Sugar during Cardio Workouts.

Blood sugar management during and after interval training

Interval Training is a type of cardio where the heart rate is going up and down during the session due to repeated bouts of short, intense activity, interrupting longer periods of lower-intensity activity or rest. Examples could include running intervals on the treadmill or playing group sports (like basketball, soccer, etc.).

Interval training can sometimes make your blood sugar levels increase rather than decrease the way it does with steady-state cardio. So, if you leave an interval training session with elevated blood sugars, it’s not necessarily because your teammates have been spiking your water bottle with juice.

What’s happening is that your body’s use of glucose increases just like it does with steady-state cardio, but your body’s glucose production outpaces it. Think of it like this: you are working hard and your body is looking out for you, so it’s dumping energy (in the form of glucose) into your system to support your activity level, an effect some feel up to 2 hours after their workout.

Yes, it can be annoying to see your blood sugar readings go up after a workout, but your body is actually not working against you. You just need to anticipate this result and work with it.

Strategies for preventing high blood sugar during and after high intensity interval training

  • Adjusting your insulin slightly up, starting 20-30 minutes after workout start (basal rate or small bolus)
  • Consider having a small meal (+bolus) prior to your workout
  • Consider adjusting basal and bolus insulin for up to 2 hours after your workout

Blood sugar management during and after resistance training

I love resistance training, not just because it makes me strong and does wonders for my curves, but because it can significantly improve insulin sensitivity. How awesome is that?

Resistance training can impact blood sugar in different ways, depending on the intensity and rep range. If you are picking up lighter weights and doing many repetitions, maybe even with little to no rest, you may see a decrease in your blood sugar, since this type of resistance training has a similar impact on the body as cardio. However, if you pick up some heavier weights and do fewer repetitions, you may see an increase in your blood sugar during the workout followed by improved insulin sensitivity up to 72 hours after your workout.

The impact and risk profile for the wacky blood sugars associated with a heavy lifting session is very similar to that of high intensity interval training, so some preventive strategies will overlap.

Strategies for preventing high blood sugar during and after resistance training

  • If using a high repetition range with lighter weight, reduce the amount of IOB (basal and bolus) by adjusting your insulin
  • For heavy weight sessions, consider adjusting your insulin slightly up, starting 20-30 min after workout start (basal rate or small bolus)
  • Always consume a small meal (+bolus) prior to your workout (you need the energy to lift)
  • Consider adjusting basal and bolus insulin for up to 72 hours after your workout

Exercise can be fun and rewarding, as well as an amazing stress reliever. But it can also be a major stress factor if your blood sugar keeps acting up. I encourage you to use the guidelines in this post as a basis to learn how your body reacts to exercise and what works for you, so that you can enjoy being active without your diabetes interfering too much.

As a final note, even if you know the general rules and your personal formula for food and insulin around workouts, you’ll still be at risk of experiencing either high or low exercise-induced blood sugars. So be like scouts: be prepared and always have your diabetes gear and glucose within reach.


Read How to Reach Your Body Goals without Obsessing over Weight by Christel Oerum and 10 Reasons for Hyperglycemia during Training by Phil Graham. 


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Christel Oerum

Christel is a blogger, personal trainer, diabetes advocate, fitness bikini champion and fitness personality. She has been living with Type 1 diabetes since 1997, and lives by the motto "There’s nothing you can’t do with diabetes – if you have the right care, technology and mindset." Christel writes Diabetesstrong.com with her husband. She blogs about health, fitness and how to be Fit With Diabetes. Follow Christel on www.diabetesstrong.com. You can also email her directly at Christel@diabetesstrong.com.