Dr. Kris Berg
The fact that vigorous exercise tends to raise BG appears to be relatively unknown to many with T1DM. However, the effect has been confirmed in a number of studies. These studies have identified an exercise threshold that elicits this response. The threshold exercise intensity occurs at or above 80% of a person’s maximum exercise capacity, which is also known as the VO2 max (maximum or peak volume of oxygen consumed in exhaustive exercise). The relevant question then becomes, what type of exercise is performed at this 80% level? The following guidelines can be used to estimate whether or not you are exercising at or above this intensity:
Why does vigorous exercise raise BG instead of lower it?
Exercise above the 80% threshold is very strenuous. Heart rate is elevated to about 90% of maximum or even higher; breathing is difficult, and we tend to huff and puff while straining to meet the energy demand of the activity. This level of exertion activates the sympathetic nervous system, which in turn elicits the “fight or flight” response. The sympathetic nervous system is excitatory, in that it helps us to meet emergency needs such as fighting for survival or completing a race or vigorous game. Strenuous exertion requires high energy expenditure, and the sympathetic nervous system helps achieve this by exciting endocrine organs such as the adrenal gland. The adrenal gland releases the stress hormones adrenaline and noradrenaline into the blood, which then stimulate the liver to release glucose at a faster rate than normal. When this rate exceeds the rate at which glucose is absorbed by active muscle tissue, BG rises.