By Sheri R. Colberg, PhD, FACSM
There is no official ideal blood glucose range to start with and maintain during physical activity, but we do know that being too low negatively impacts performance, as does being too high. As for what blood glucose target or range most athletes aim for, it depends on a number of factors, including the type, intensity, and duration of their activity. A consensus statement about exercise and type 1 diabetes published in The Lancet in 2017 suggested that a reasonable target for most people doing aerobic exercise lasting up to an hour is 126 to 180 mg/dL (7.0 to 10.0 mmol/L), only aiming higher for added protection against lows in some situations (1).
For anaerobic (power) exercise or high-intensity interval training sessions, you may want to start with your glucose lower—around 90 to 126 mg/dL (5.0 to 7.0 mmol/L)— simply because the intensity of the activity may cause your blood glucose to stay more stable, fall less than during aerobic workouts, or possibly even rise slightly (1).
An ideal or optimal blood glucose target during most physical activities may be in the range of 108 to 144 mg/dL (6.0 to 8.0 mmol/L).
Most of the athletes surveyed for The Athlete’s Guide to Diabetes (2019) said the range of 80 to 180 mg/dL (4.5 to 10.0 mmol/L) was their stated target during exercise. Only a few of them aim for lower or higher than that range, although most admittedly have a narrower target.
Canadian Scott L. from British Columbia agrees with recommended ranges for performance reasons, saying, “My aim is to be 6.0 to 8.0 mmol/L [108 to 144 mg/dL]. I feel the strongest at 6.0 mmol/L [108 mg/dL], but it gives me less opportunity to catch lows. Above 10.0 mmol/L [180 mg/dL], I start to feel a little sluggish—and above 15.0 mmol/L [270 mg/dL] very sluggish!”
But the blood glucose target depends on the activity and other factors. Just to give you a few examples, Chris C., a resident of New Jersey, tries to keep her blood glucose as close to 100 mg/dL (5.6 mmol/L) as she can, saying, “With high-intensity interval training my glucose will jump here and there throughout the workout with the intensity of the exercises. As soon as I am done, though, my glucose usually starts to drop.”
New York resident Riva G. uses a similar range of 80 to 150 mg/dL (4.5 to 8.3 mmol/L) for all her activities, but she likes to start on the higher end for walking. Jason O. of Ireland also varies his target based on his activity: 126 to 180 mg/dL (7.0 to 10.0 mmol/L) for cycling, just to make sure he has some leeway if he needs to make a big effort, and a tighter range of 90 to 144 mg/dL (5.0 to 8.0 mmol/L) for walking. For surfing, he aims for 5.5 to 9.0 mmol/L (100 to 162 mg/dL) in the water but uses a different target range of 4.5 to 7.5 mmol/L (80 to 135 mg/dL) for all other sports. Likewise, Ginger V. from Vermont sets the lower end of her range at 80 mg/dL (4.5 mmol/L) for all her activities, but she varies the higher end depending on whether she is doing fasted (120 mg/dL [6.7 mmol/L]) or nonfasted (150 mg/dL [8.3 mmol/L]) exercise.
The key is to find out what works best for you and maintain your blood glucose in that range during activities. Keep in mind that your glucose target may vary with the type of activity you do (mode, intensity, duration, etc.), exercise timing, insulin (or other medication) regimen, recent or concurrent food intake, environmental conditions, and multiple other factors. It’s not usually a one-size-fits-all solution.
1. Excerpted from Colberg, SR, Chapter 5, “Using Technology and Monitoring to Enhance Performance,” in The Athlete’s Guide to Diabetes: Expert Advice for 165 Sports and Activities. Champaign, IL: Human Kinetics, 2019.
Sheri R. Colberg, PhD, is the author of The Athlete’s Guide to Diabetes: Expert Advice for 165 Sports and Activities (the newest edition of Diabetic Athlete’s Handbook), which is now available through Human Kinetics (https://us.humankinetics.com/products/athlete-s-guide-to-diabetes-the), Amazon (https://amzn.to/2IkVpYx), Barnes & Noble, and elsewhere. She is also the author of Diabetes & Keeping Fit for Dummies. A professor emerita of exercise science from Old Dominion University and an internationally recognized diabetes motion expert, she is the author of 12 books, 28 book chapters, and over 400 articles. She was honored with the 2016 American Diabetes Association Outstanding Educator in Diabetes Award. Contact her via her websites (SheriColberg.com and DiabetesMotion.com).