Physical exercise is one of the foundations of diabetes treatment. It has numerous positive effects, from reducing cardiovascular risk factors to improving quality of life. Nevertheless, as with any treatment, it can also have some adverse effects. Hypoglycaemia is definitely the one that causes most concern for people with diabetes.
Simply put, it could be stipulated that physical exercise increases glucose consumption in muscle cells. Therefore, it is to be expected that, when exercising, blood glucose levels decrease. This is what generally happens when playing sports or exercising.
But this is not always the case; in many cases, after exercising, blood sugar levels do not only not decrease, but can even increase.
This phenomenon can be explained by the body’s blood sugar regulation system. As stated above, while exercising, muscle cells consume glucose but simultaneously, the release of glucose stored in the liver is activated. Therefore, the end result is a balance between the glucose released by the liver and the glucose consumed by muscle cells.
Each type of exercise will have a different effect on blood glucose levels. Particularly, the intensity at which one exercises is a key factor. The higher the intensity, the more muscle consumption, but also the more glucose is produced and released by the liver. The glycaemic effect of each type of exercise can be summarised as:
|Type of Exercise
|Effect on glucose levels
|Short duration and low intensity exercises
|Walking, cycling to work or gentle swimming.
|They do not usually alter blood glucose levels, because glucose muscle consumption is low. Nevertheless, if they are performed for a longer period of time, hypoglycaemia may occur.
|Long duration and moderate-high intensity exercises
|Running, cycling or swimming for 1 hour or more.
|They normally represent a high glucose muscle consumption. This consumption is so high that glucose production in the liver is not capable of offsetting it, so as the minutes go by blood glucose levels tend to drop.
|Short duration and high intensity exercises
|Weight training, combat sports, athletic sports such as 100 or 200 m or throws.
|They usually maintain or increase blood glucose levels while exercising. In these cases glucose consumption is less than the amount produced by the liver.
|Football, basketball or volleyball.
|They do not have a clear effect, since they combine high intensity moments with lower intensity periods. In these cases, response to exercise must be assessed individually.
As well as the type of exercise, there are other basic factors that must be taken into account with regard to blood glucose level regulation while exercising. Among them, the following three are particularly noteworthy:
- Blood insulin levels. For people following an insulin treatment, blood insulin levels vary significantly throughout the day. Physical exercise significantly increases the effect of insulin, increasing the likelihood of hypoglycaemia. Therefore, the same exercise performed at different times of day can lead to different blood glucose levels.
- Competitive stress is a factor that is difficult to control, but in the case of people with diabetes, it can lead to pronounced increases in blood glucose levels. Nervousness before a competition can stimulate the release of glucose by the liver, resulting in hyperglycaemia.
- Hypoglycaemia after exercise. The hypoglycaemic effect of physical exercise can persist for a period of up to 12-24 hours after the end of the activity. Special attention must be given to long duration aerobic exercises, since these are the ones that tend to lead to post-exercise hypoglycaemia, particularly throughout the night.
Many factors must be taken into account with regard to blood glucose levels during and after exercising in people with diabetes. Despite this, the benefits of physical exercise are such that it must be promoted among all diabetics.
Written by Mr Serafín Murillo García, with a Diploma in Human Nutrition and Dietetics, a Master’s in Sports Performance and a Master’s in Diabetes Education by the University of Barcelona. Associate Professor at the University of Barcelona. Diabetes Educator and Nutritionist at Fundació RCF and Institut Diabetes Activa. Author of the manual ‘Diet for children with diabetes’ and ‘Type 1 diabetes and Sport, for children, adolescents and young adults’ and co-author of the website www.diabetesalacarta.org. Mr. Serafín is part of the editorial committee at SocialDiabetes.