Home / Resources / Featured Writers / Dealing with Exercise-Induced Hypoglycemia

Dealing with Exercise-Induced Hypoglycemia

Feb 17, 2009

Too often our patients who are very active start to decrease their participation in sports and other physical endeavors. Frequently, this is because they are experiencing hypoglycemia and have no idea how to prevent this from happening. Sheri Colberg, Ph.D., FACSM, helps you to understand what is going on and what to do in Dealing with Exercise-Induced Hypoglycemia.

Dealing with Exercise-Induced Hypoglycemia


By Sheri Colberg, Ph.D., FACSM

Experiencing bad low blood sugar reactions is one of the main factors that lowers the quality of life of those with diabetes. Even the fear of such lows is enough to increase your anxiety levels. You can do several things, however, to lower your risk, including becoming more aware of the possible symptoms of hypoglycemia.

SheriRecognizing the Symptoms of Hypoglycemia

You really need to know all the possible symptoms of lows, both at rest and during exercise, to detect and treat it early. As you know, normal fasting blood sugars range from 70 to 99 mg/dl (3.9 to 5.5 mmol/L). Although hypoglycemia is technically any blood sugar below 70 (3.9 mmol/L), how low it has to go to cause symptoms of hypoglycemia varies. For instance, if you have been in poorer control, sometimes you will get symptoms while your blood sugars are still normal if they drop rapidly, without ever getting as low as 70 (3.9 mmol/L). If you’re in really tight control, your symptoms may not start until you reach 55 mg/dl (3.1 mmol/L) or lower. Some people have hypoglycemic unawareness, which means that they either don’t have or fail to recognize the usual symptoms. This condition appears to be more common in people with tight control or frequent lows (more on this later).

The hormones that your body releases during exercise result in some of the same symptoms as hypoglycemia, which can sometimes make it hard to distinguish between the onset of hypoglycemia and the normal physical sensations associated with exercising, such as fatigue, especially during exercise in cold weather. Typical symptoms of hypoglycemia include shakiness, hand trembling, tingling of your hands or tongue, sweating, mental confusion, irritability, poor physical coordination (i.e. clumsiness), and visual changes, among others.

Symptoms may also vary among people and by type of physical activity. By way of example, one athlete with diabetes reportedly sees a spot develop in one eye while running every time he becomes hypoglycemia while another exerciser begins kicking the back of one heel with the toe of his other foot while running when he starts to get low. Your symptoms can also change over time when your fitness levels improve or worsen, so you should learn to recognize your unique set. Be aware that the symptoms can also differ from workout to workout depending on the type of exercise that you’re doing, the rate of decline of your blood sugars and the environmental conditions.

Make certain that you carry something with you to treat your lows, such as glucose tablets and gels or hard candy. You may possibly step out of your house and forget to bring something with you, only to have a bad low with nothing available to treat it. One hard-training triathlete who always carries something with her during her long, strenuous workouts often goes out to walk the dog without bringing anything along and has her blood sugars drop like a rock. (Perhaps for her, taking the dog out just doesn’t seem like enough exercise to cause low blood sugar, but it certainly can.) The maxim for treating exercise-induced lows should be the same as the Boy Scout motto: “Always be prepared.”

Testing for Hypoglycemia

In reality, it’s not always easy to tell right away if your blood glucose level is too high or low right when you start feeling funny, especially when you’re exercising. In fact, when your blood sugars are changing rapidly—either going up or down—you often can’t tell which way they’re going until your symptoms progress. If you’ve been running high for a while or you’re exercising hard when your blood sugars start to decrease rapidly, you may feel hypoglycemic even when your blood sugars are still elevated, or you may not even be able to tell at all.

Regardless of your type of diabetes, testing your blood sugars at different times, more often than just before meals and at bedtime, can help reveal trends that might not be apparent otherwise. Because postmeal glucose excursions may be as important in causing diabetic complications as your overall glucose control, limiting such spikes may be the key to preventing microvascular complications like diabetic retinopathy. Thus, testing not just before meals but also occasionally one hour and two hours afterward can let you know how your various meals are affecting your blood glucose levels and how much variability you are experiencing.

Although the standard recommendation is to check two hours after your first bite of a meal, you may actually peak at 72 minutes after eating and have a variation of 23 minutes either way—based on the results of studies using continuous glucose monitoring. The best idea, then, is to vary your blood glucose testing instead of testing only before meals and at bedtime, especially when you add exercise to the mix. The more you test, the easier it is to figure out what your patterns are, which way your blood glucose levels are going, and when you’re likely to drop, either during or after exercise.


This column is excerpted from Diabetic Athlete’s Handbook (released November 2008 from Human Kinetics), which contains essential exercise-related information and examples for type 1 and type 2 diabetic exercisers. Look for it in stores or find links to places to buy it online on www.shericolberg.com, along with additional information.