Vigorous Exercise Can Elevate Blood Glucose in Type 1 Diabetes

The notion that all exercise lowers blood sugar levels in people with type 1 diabetes (T1D) is outdated, according to research.

Studies have identified that vigorous activity - at or above 80 percent of our maximum exercise capacity - tends to elevate blood glucose. This glucose-raising intensity level can be reached in a couple of ways:

  1. By performing a vigorous activity (e.g., cycling, running, swimming) continuously for several minutes or longer, where breathing becomes so rapid and deep that conversation is not an option.
  2. By enjoying an activity that alternates short bursts of speed with periods of moderate exercise—such as happens playing soccer, basketball, football, singles tennis, or wrestling.

Whether the exercise intensity is continuous or comes in short bursts, if it pushes the 80 percent activity threshold blood sugar tends to rise because of the way our body responds to the demands of exertion.

Exertion and Glucose

Intense exertion activates our sympathetic nervous system, triggering the “fight or flight” response. This response helps our body get what it needs for survival, or to engage in a strenuous activity.

Since strenuous activities require considerable energy, the sympathetic nervous system stimulates endocrine organs, such as our adrenal glands, to release stress hormones (e.g., adrenaline, noradrenalin) into the bloodstream. These stress hormones prompt the liver to release glucose at a higher than normal rate. When the liver’s glucose release exceeds the glucose being absorbed by active muscles, our blood glucose elevates.

Moderate exercise does not activate our “fight or flight” response so the liver is never prompted to release extra glucose, and blood sugar typically decreases.

Intense vs Moderate Activity

To compare the effects of moderate and intense exercise, one study had subjects with T1D pedal a cycle using maximum exertion for four seconds, and then cycle for two minutes at an easier pace; they followed this alternating pattern for 30 minutes. The intention was to mimic the high and low exertion levels experienced in many sports or games.

The researchers also had some T1D subjects exercise at a continuous moderate pace (40 percent of maximum intensity level) for 30 minutes. The study results showed that:

  • Blood glucose was elevated in those alternating high and low intensity exercise.
  • Blood glucose decreased in the moderate exercisers although their exercise involved less total work.

Another study revealed that just a single ten-second sprint within a moderate exercise session can help limit the decline of blood glucose. This might inspire those who exercise at a moderate pace to add a few bursts of speed, or exertion to their routine.

Must Monitor

Knowing that different types of exercise have a different effect on glucose levels does not mean people can assume that a certain activity will raise, or lower their blood sugar.

The only way to know how an exercise or sport affects individuals is by doing extra glucose monitoring. After carefully logging exercise type, intensity, and blood sugar levels people can determine the unique glucose effects of the sports they participate in. Then, carb intake before, during, and after these activities can be adjusted appropriately.

Those with T1D who are inexperienced with making insulin or carb adjustments related to activity level should discuss what to do with a doctor, or diabetes educator.

While it might seem the effect of intense exercise on blood sugar is just another doggone thing to think about, this knowledge can give active individuals better control over their glucose levels. Plus, once people determine that vigorous exercise elevates their glucose they may feel less worried about the risk for hypoglycemia, and enjoy those activities more.

Source: Kris Berg/Diabetes Health

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