Blood Sugar and Exercise

We’ve all felt how our blood sugar can impact us: that infamous midday crash that leaves us dragging through the rest of the day. But our blood sugar levels are actually part of an incredibly complex biological system with wide reaching effects. In addition to its bearing on our daily lives, our blood sugar can both effect and be effected by our exercise program.


How Blood Sugar Works

The term blood sugar, or blood glucose, refers to a ratio of how much sugar is in – you guessed it – your blood. That glucose is taken from the food you eat and acts as the primary fuel source for just about everything that happens in your body down to the cellular level. By having some of it simply floating through your blood stream, it is readily available for the cells to absorb and use. Too much glucose, however, can damage the cells. A healthy blood glucose level is between 90 and 110 mg/dl.

Two hormones, both made and release by the pancreas, work to maintain this balance. Insulin is used when blood glucose levels are too high. Once its in the blood stream it tells the cells to absorb more glucose and has the liver store more for later use. This removes the sugar from the blood and lowers the blood glucose.

When there is too little sugar in the blood, glucagon is sent out. Glucagon lets the liver know that it’s time to release all of the store glucose into the blood stream.


Fitness and Blood Sugar

What’s the typical gas mileage like on your car? Now imagine that, instead of driving the way you normally you do, we expected your car to perform at double the speed? Or what if we hitched a half-ton trailer to it? Among other things that would happen to your car, your gas mileage would drop significantly.

Your muscles work the same way. When we place higher demands on them, our muscles demand more fuel more rapidly. Over-training, specifically strength training, can actually cause an increased sensitivity to insulin, causing your cells to absorb too much blood sugar too quickly. This can result in a post-training crash but can also affect you at other times.

When you eat a carbohydrate-rich food, those carbs quickly become glucose. In response to the rise in glucose, your body produces insulin. If you’re overly sensitive to insulin, though, this will cause your blood sugar to crash as a form of reactive hypoglycemia.

Studies suggest, however, that endurance training can have the opposite effect. Although the link isn’t fully understood, endurance training seems to balance insulin sensitivity. Additionally, during this type of exercise fat used more readily for fuel than carbohydrates so there is less of an impact on your blood sugar levels.


Finding Your Center

The study of any biological function will inevitably bring your back to the concept of homeostasis. This is the idea that our bodies are constantly self-regulating by means of competing forces to maintain a balance. Blood sugar is a prime example of this.

Since exercise can so easily throw off this delicate balance and our exercise performance can be negatively affected by it, how can we maintain health levels?

Diet is key. Make the shift to six small meals a day, consisting mainly of protein and complex carbohydrates. These foods, like whole grains and starchy vegetables, break down slowly and don’t cause an insulin spike or the resulting crash. Similarly, avoid simple sugars like soda and baked foods since this type of carbohydrate is broken down quickly and will cause your blood sugar to crash.

Has your exercise program been affected by your blood sugar? How have you overcome it? Please share your experience with us in the comments!





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About jonathan.thompson

Jonathan Thompson is a Certified Personal Trainer and Running Coach with the American Council on Exercise, specializing in nutrition. In addition to his real-world experience working with clients, his articles and blogs on fitness advice have been published on many websites and magazines.