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  • Sheri Colberg, PhD

Webinar Q&A with Dr. Sheri Colberg: Part 2

I recently gave a webinar for the American College of Sports Medicine (and Technogym) that reached almost 1,200 participants in real time. You can watch the webinar, titled “The Role of Physical Activity in Type 2 Diabetes Management and Prevention,” posted on Youtube.



While the Q&A portion was done live, it was not included in the webinar recording. Plus, there were many additional questions for which there was no time to discuss. This article addresses the second half of those questions (the rest were answered in November 2021).


Q: Please mention blood sugar level prior to as well as fluid and hydration intake prior to ANY exercise is crucial to predict glycemic response.... regular blood glucose checks are key until you know how they respond.


A: The guidelines are that you should not begin exercise with a 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, just make sure you have enough insulin “on board” to counterbalance the glucose-raising hormones that get released during physical activity. The harder 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, as well as avoid exercising during the peak heat of the day or in direct sunlight to prevent overheating. These precautions are particularly important when someone has been experiencing hyperglycemia (elevated blood glucose levels) that can lead to dehydration or if someone has 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 really depends on the individual. Adults with type 2 diabetes not taking insulin or sulfonylurea oral 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 important to check before, occasionally during, and even at varying intervals of time after activities to prevent both lows and highs and to treat them more quickly. Frequent monitoring also helps with establishing usual patterns, trends, and responses that make it easier to predict what insulin regimen or food changes may be needed to keep blood glucose levels balanced, especially you may be prone to developing late-onset hypoglycemia following an activity that is particularly long or intense.


Q: In order to avoid exercise-induced hypoglycemia, what are the normal values of glucose monitoring 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 normal responses. Most people like to start in the range of 70 to 180 mg/dL (3.9 to 10.0 mmol/L), but it really depends. For example, if you’re going to do early morning exercise (before insulin or food), your blood glucose may raise due to the higher levels of insulin resistance at that time of day. Many people actually 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 actually give small amounts of insulin prior to doing intense early morning workouts to prevent going too high.


As for hypoglycemia, it can have a variety of symptoms, including shakiness, visual spots, lethargy, extreme fatigue, and more. To make it more challenging, the symptoms can vary by the person and by the activity or time of day. Learn to recognize your own symptoms by confirming your blood glucose levels whenever any symptoms arise. Anything with glucose works fastest to treat a low, but you can use a variety of 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 with respect to common diabetes medications?


A: There are two position/consensus statements with compiled information about being physically active with diabetes that would particularly useful when it comes to 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 important 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 fine. 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 carbohydrate. Fat is the primary fuel during all recovery periods. Intramyocellular lipids, therefore, are the primary fuel used during periods of rest, which is most of the time. Just try to maximize your total calorie expenditure from 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. For them, it may be more appropriate 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 can 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?


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 harder exercise, due to a reduced circulation and supply of blood and oxygen to those peripheral areas. While it may appear that exercise makes things worse, given the pain often associated with it, the opposite is true. It can actually improve circulation with 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). Doing activities at any intensity that is possible, therefore, 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 to 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 in them 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. It really depends on what data sets are most important to you.


Check back last month for Part 1 of this webinar-related Q&A!

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