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How to Prevent Exercise Induced Hypoglycemia

Guest Post Written By: Taylor Proffitt

 type one diabetes

For individuals with Type 1 Diabetes on insulin, low blood sugar due to exercise is highly likely if the appropriate preventative measures are not taken. However, diabetes and the fear of exercise induced hypoglycemia should never deter someone from engaging in any type of physical activity. In this blog post we will discuss 4 tips on how to prevent low blood sugar while exercising.

Insulin is a hormone that serves many purposes. One of which includes sending signals to the liver to absorb glucose from the blood which is then converted into the stored molecule, glycogen. Unlike endogenous insulin (insulin created by the pancreas) which increases and decreases automatically based on the body’s need, a Type 1 Diabetic is in control of the amount of insulin present throughout their body.

When exercising, glucose is used as energy, thus decreasing the amount of glucose in the blood. For an individual that does not have Type 1 Diabetes, when blood glucose begins to drop as a result of exercise, the pancreas naturally begins decreasing insulin production and the liver begins releasing the stored glucose to maintain the blood glucose level. However, for individuals with Type 1 Diabetes, this process does not occur (naturally).

For someone with Type 1 Diabetes, if insulin is being delivered at the same rate as when not exercising, blood glucose will continue to drop since as you may recall, insulin sends signals to the liver to prevent the release of stored glucose thus resulting in a low blood sugar.

So how do we prevent exercise induced hypoglycemia?  

1. Perform weight training THEN cardio: 

Believe it or not, weight/resistance training can actually increase blood glucose by increasing counter-regulatory hormones such as growth hormone, cortisol and catecholamines. All of these hormones cause an increase in blood glucose. On the contrary, cardio, especially steady state cardio, decreases blood glucose.

So by weight training first then performing cardio second, it is allowing your glucose to rise slightly giving you more of a “cushion’ when it does begin to drop from cardio, ultimately preventing a low blood sugar.

2. Decrease the amount of insulin on board while exercising:

For people with Type 1 Diabetes, insulin in delivered both in a basal and bolus form which means a small amount of insulin is being continuously delivered (basal) while larger doses are administered for meals and elevated blood glucose (bolus). As I mentioned previously, low blood glucose during exercise occurs due to an overabundance of insulin. Therefore, by decreasing the amount of circulating insulin, low blood glucose is less likely to occur during exercise.

When taking a long-acting basal insulin injection, this cannot be altered around activity. However, for individuals on pump therapy, basal insulin can be temporarily reduced to help prevent low glucose during and after exercise. Setting a temporary basal 1-2 hours before exercise, during exercise and up to 2+ hours after exercise can help prevent low blood glucose. However, the percentage and time of decrease in basal needed differs for every individual as well as based on the exercise being done.

In addition to decreasing basal insulin, another effective way of preventing exercise induced low blood glucose is to reduce the amount of Insulin on Board (IOB) or “active insulin” while exercising. So how is this accomplished? Some individuals choose to not eat within 3 hours of exercising so the mealtime insulin taken 3 hours prior is now done working and there is no “active insulin” circulating. However, this is not feasible for everyone as many individuals feel they need to eat before exercising for greater energy and stamina. If eating within 90 minutes of a meal, decreasing the dose for that meal will help prevent a low glucose from occurring during exercise. Below is a chart created by Gary Scheiner MS, CDE which demonstrates the bolus reduction needed depending on the duration and intensity of a workout:

exercise with type one diabetes

Scheiner MS, CDE, G. (2012). ​Exercise and Pump Therapy. Retrieved from ​ & pump therapy for ADA pump book.pdf

Remember, exercise will use glucose for energy during a workout BUT the glucose lowering effect from exercise can last up to hours after the workout which accelerates the muscle cells’ uptake of glucose. Decreased insulin needs may last for hours after exercise as a result. Exercise can also increase insulin sensitivity thus resulting in a decreased amount of insulin needed. 

3. Eat before your workout: 

Not only is it important to eat nutrient dense foods in order to fuel and recover from your workout properly, but it can also serve as a means of preventing low blood sugars during exercise. Eating a meal 60-90 minutes before exercise with low glycemic index carbohydrate sources in combination with a lower meal-time insulin dose results in more stable blood glucose throughout a workout. My favorite pre-workout meal is PROATS = oatmeal mixed with protein powder and topped with some PB. This meal includes a well balanced mix of all macronutrient components including carbs, protein and fat. 

Oatmeal has a very low glycemic index (GI) and because of this is digests slowly, throughout the workout, preventing glucose from spiking or dropping suddenly. If a meal is eaten with no insulin, then hyperglycemia (high blood sugar) is likely to occur even when exercising. 

Now if exercising before eating or in between meals, having a high GI snack (rice cakes, fruit, etc.) right before a workout, without taking insulin, is also beneficial as it provides quick energy and glucose which will be used during the workout. Again, the amount of carbs needed depends on the individual as well as the duration and intensity of the workout: 

carbohydrate replacement t1d

Scheiner MS, CDE, G. (2012). Exercise and Pump Therapy. Retrieved from & pump therapy for ADA pump book.pdf 


4. Correct with caution: 

In contrary to discussing low blood glucose during exercise, blood glucose can also go high during or after a workout, which can occur for a multitude of reasons. As discussed above 

in regards to resistance training and counter-regulatory hormones and its ability to raise blood glucose, individuals that do experience high blood glucose during or immediately following physical activity should correct with caution! A full dose correction should NOT be given in most circumstances because as you may recall, once the counter-regulatory hormones released while exercising begin to decrease after the workout is finished, blood glucose will also begin to decrease naturally. A full dose correction would likely cause a subsequent low blood glucose. Administering a half dose correction for a high blood glucose after a workout typically results in a better outcome and prevents delayed hypoglycemia. 

Variable glucose responses to different types of physical activity make uniform recommendations nearly impossible. When it comes to preventing low blood glucose while exercising, it usually comes from a combination of all 4 tips! Blood glucose levels while exercise for an individual with Type 1 diabetes can be managed most effectively through the manipulation of food intake, insulin dosing AND trial and error. But even when all the right measures are taken, exercise induced hypoglycemia can still occur so ALWAYS remember to pack low BG treatment whether it be juice, glucose tabs, gummies, etc. in case your blood glucose does drop! 

Try not to get frustrated and do not give up exercise because of initial blood glucose instability. Physical activity is SO vitally important to all aspects of health, both physically and mentally, and worth the little bit of extra work required to maintain adequate blood glucose during and around exercise.