Dec 4, 2021
Author: Sheri R. Colberg, PhD, FACSM
- Part 2 of this Q&A with our diabetes exercise expert covers pre-exercise glucose checks, exercise-induced hypoglycemia, and more.
Q: Please mention blood sugar level before as well as fluid and hydration intake before ANY exercise is crucial to predict glycemic response…. regular blood glucose checks are essential until you know how they respond.
A: The guidelines are that you should not begin the exercise with blood glucose >250 mg/dL (13.9 mmol/L) with moderate or high levels of blood or urinary ketones. If you don’t usually test for ketones, make sure you have enough insulin “on board” to counterbalance the glucose-raising hormones that get released during physical activity. The more complex the exercise is, the more of these hormones get released.
The guidelines also suggest that people should use caution during activities when starting with a blood glucose >300 mg/ dL (16.7 mmol/L) without excessive ketones, stay hydrated, and only begin if feeling well. For instance, if you take insulin and just ate a big meal, exercising right after when you may be experiencing a spike is usually okay because you have enough insulin in your body to bring the glucose levels down with activity.
As for hydration, drink adequate fluids before, during, and after exercise and avoid exercising during the peak heat of the day or in direct sunlight to prevent overheating. These precautions are essential when experiencing hyperglycemia (elevated blood glucose levels), leading to dehydration or autonomic (central) nerve damage that can impair normal heat dissipation during exercise.
Q: What are your recommendations for glucose testing before, after, or during exercise?
A: It depends on the individual. Adults with type 2 diabetes not taking insulin or oral sulfonylurea medications may not need to check because their blood glucose is unlikely to drop too low during activities—but they may want to check to be motivated by its ability to lower blood glucose, especially during post-meal spikes.
If you use insulin, it is essential to check before, occasionally during, and even at varying intervals after activities to prevent lows and highs and treat them more quickly. Frequent monitoring also helps establish usual patterns, trends, and responses that make it easier to predict what insulin regimen or food changes may be needed to balance blood glucose levels, especially if you are prone to developing late-onset hypoglycemia following an activity that is particularly long or intense.
Q: To avoid exercise-induced hypoglycemia, what are the normal glucose monitoring values before starting exercise? Is there a target glycemic range that you would recommend for those with Type 1 diabetes to begin exercise to prevent hypo during activity? Also, how can people recognize and respond to hypoglycemic reactions?
A: A good starting blood glucose level can vary with the activity, time of day, and expected responses. Most people like to start in the range of 70 to 180 mg/dL (3.9 to 10.0 mmol/L), but it depends. For example, if you’re going to do early morning exercise (before insulin or food), your blood glucose may rise due to the higher levels of insulin resistance at that time of day. Many people choose to exercise then so that their risk of going low is minimal. However, others prefer to exercise with slightly more insulin on board (but not too much) later in the day to avoid exercise-related highs, especially when doing more intense workouts. Some people give small amounts of insulin before doing intense early morning workouts to prevent going too high.
As for hypoglycemia, it can have various symptoms, including shakiness, visual spots, lethargy, extreme fatigue, and more. The symptoms can vary by person and the activity or time of day to make it more challenging. Learn to recognize your symptoms by confirming your blood glucose levels whenever any symptoms arise. Anything with glucose works fastest to treat a low, but you can use various carbohydrate sources and follow up with snacks with a balance of carbs, protein, and fat if lows tend to persist or recur over time.
Q: What resources would you recommend for additional information regarding clinical exercise programming concerning common diabetes medications?
A: There are two position/consensus statements with compiled information about being physically active with diabetes that would be particularly useful for diabetes medications and their impact on physical activity. One is an American Diabetes Association position statement from 2016 (PMID: 27926890), and the other is a consensus statement on type 1 diabetes from 2017 (PMID: 28126459).
Particularly for anyone using insulin or taking sulfonylureas (and possibly meglitinides within 2-3 hours of physical activity), it is essential to carry rapid-acting carbohydrate sources during activities to treat hypoglycemia and have glucagon available to treat severe hypoglycemia (if you are prone to developing it).
Q: Diabetes type 2 has been related to intramyocellular lipid accumulation. As fat oxidation is optimized at a low exercise intensity, would you recommend low exercise intensity over high-intensity exercise for patients with diabetes?
A: No. Any intensity of exercise that someone with type 2 diabetes can do is acceptable. While it is true that slightly more fat is used during lower intensities compared to higher ones, the primary fuel used by the body during most moderate or higher-intensity work is carbohydrates. Fat is the primary fuel during all recovery periods. Intramyocellular lipids, therefore, are the primary fuel used during rest periods, which is most of the time. Just try to maximize your total calorie expenditure from the physical activity without worrying about exercise intensity. (In other words, completely ignore anything that tells you that you are in a “fat-burning range” as it is incorrect and irrelevant.)
Q: What precautions need to be taken if there is peripheral neuropathy?
A: It is generally recommended that people with moderate to severe peripheral neuropathy (loss of sensation in the feet) limit or avoid activities that may cause foot trauma, such as prolonged hiking, jogging, or walking on uneven surfaces. It may be more appropriate for them to engage in non-weight-bearing exercises (e.g., cycling, chair exercises, swimming); however, they should avoid aquatic exercise with unhealed plantar surface (bottom of the foot) ulcers. It is also important to check feet daily for signs of trauma and redness. Other precautions include choosing shoes and socks carefully for proper fit and wearing socks that keep feet dry, such as some of the newer athletic socks that are polyester-cotton blends. Finally, neuropathy can affect both gait and balance, so they should avoid activities requiring excessive balance ability.
Q: I work with many folks who have kidney failure due to diabetes. Are there any precautions even though the client has been medically cleared?
A: Yes, the main precautions for these individuals revolve around avoiding exercise that causes excessive increases in blood pressure, such as heavy weight lifting, high-intensity aerobic exercise, and anything that causes breath-holding. For most, high blood pressure is common, and lower intensity exercise may be necessary to manage blood pressure responses and fatigue. The good news is that light to moderate exercise is possible during dialysis treatments if electrolytes are managed properly. A recent study showed that people on dialysis could safely engage in aerobic, resistance, or combined training with good outcomes on fitness, blood pressure, and metabolic function (PMID: 31865607).
Q: One of the complications you mentioned was peripheral arterial disease. The exercise pattern is less in these individuals. What do you think in that aspect when we can’t do higher intensity exercise? What pattern should we focus on?
A: Peripheral artery disease occurs when significant amounts of plaque are present in the blood vessels supplying the legs and feet. This blockage can cause pain and leg cramps, particularly during more strenuous exercise, due to reduced circulation and supply of blood and oxygen to those peripheral areas. While exercise may make things worse, the opposite is true, given the pain often associated with it. In addition, it can improve circulation with the formation of new, collateral blood vessels.
In general, the intensity of activity mainly impacts the recruitment of additional muscle fibers, specifically faster twitch fibers that are more anaerobic in nature than aerobic. Although fitness gains may be lesser with lower-intensity activities, doing anything at a low or moderate intensity still confers many health benefits, including increasing blood flow to areas with some artery blockage and enhancing oxygen consumption in engaged muscles (PMID: 28385410). Therefore, doing activities at any possible intensity should be encouraged, and walking is fine for most people to engage. People should be encouraged to try alternate activities when pain in their legs is more severe or intolerable during a given activity.
Q: Which fitness trackers monitor blood glucose levels, and how does this work?
A: If discussing only FDA-approved glucose monitors, at the current time, a person has to wear a separate continuous glucose monitoring (CGM) device like the latest ones from Dexcom that can transmit its readings to a fitness monitor, such as select Apple or Fitbit smartwatches, or apps like the one associated with Fitbit or other trackers. A compatible smartphone is required to display data on an Apple Watch, and the Freestyle Libre CGMs work through a linked phone app as well. This connectivity is currently being updated and enhanced, so check the latest devices for specifics on which ones connect and how to set them up.
Q: Do you have any apps you recommend to track exercise?
A: There are so many different apps, and most of the latest smartphones have accelerometers that can track steps or distances traveled. I use one called “Map My Walk” that tracks most types of activity (not just walks) and gives distance, time, and more. Many others also estimate calorie use. So it depends on what data sets are most important to you.
Check back to last month’s Part 1 of this webinar-related Q&A!
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). She is also the author of Diabetes & Keeping Fit for Dummies, co-published by Wiley and the ADA. A professor emerita of exercise science from Old Dominion University and an internationally recognized diabetes motion expert, she is the author of 12 books, 30 book chapters, and over 420 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).