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A REMINDER – this blog post is written by a healthcare professional but no changes should be made to the treatment of your condition without consultation with your own Diabetes team.
Author: Dr Matthew Campbell | PhD ACSM-CEP MIFST RNutr FHEA BSc hons.
Read time: 10 minutes
During a football match, you will find yourself walking, jogging, running, sprinting, jumping, dribbling, striking the ball, changing direction, as well as coming into contact with the opposition (and possibly arguing with the referee). This places a significant demand on our body’s physiological energy systems as it tries to cope with repeated changes in exercise intensity1.
How does the body use blood glucose during exercise?
The body requires energy to exercise, and this is generated by breaking-down various fuels. The main fuels used for exercise are carbohydrate and fat. Everyone (including professional footballers) has enough fat stored away to the meet the body’s fat-derived energy requirements for a football match. However, for higher intensity exercise the body relies more on carbohydrate but has only a limited storage capacity. Carbohydrate is stored in the form of glycogen – bundles of individual glucose molecules packaged together. During exercise, muscles convert stored glycogen into glucose which is then converted into energy. Muscles are also able to extract glucose directly from the blood to help meet their energy demands, and as exercise intensity and duration is increased more and more glucose from the blood is pulled into muscle – this can cause low blood glucose levels, even in people without type 1 diabetes.
Why do people with type 1 diabetes have an increased risk of hypoglycaemia during exercise?
In people without type 1 diabetes, insulin levels are regulated and are reduced in response to exercise. This enables two things; firstly, it limits muscle tissue from extracting excessive amounts of glucose from the blood; secondly, lower insulin levels allow the liver to release more glucose into the blood2. Think of this as trying to fill a bucket with a hole in the bottom… if the liver can release enough glucose into the blood to meet the rate at which glucose is being removed by muscle (and other tissues) then blood glucose levels will remain stable. If the rate at which glucose is removed from the blood exceeds the rate at which blood glucose is being replaced, then fatigue, reduced performance, and potentially hypoglycaemia will ensue. Importantly, in type 1 diabetes, insulin levels are the result of the previously administered dose and/or background insulin. This means that once in the body, insulin is unregulated and does not decrease in response to exercise. This results in two things; firstly, higher insulin levels promote excessive glucose removal from the blood; secondly, higher insulin levels prevent the liver from releasing sufficient glucose into the blood to meet demand. This will result in hypoglycaemia.
Does playing football mean I will have a hypo?
Although most people associate exercise in type 1 diabetes with hypoglycaemia3 – i.e., the ability of exercise to lower blood glucose to potentially dangerous levels – not all forms of exercise lower blood glucose acutely4-8. Whereas continuous or prolonged aerobic-based exercise (like running a 10K or half-marathon at a steady pace) carries with it a heightened risk of hypoglycaemia8, high-intensity types of exercise (like lifting weights or sprinting) often cause a short-term rise in blood glucose levels4,6,9. Intermittent types of activity which involve repeated bouts of high-intensity activity interspersed with lower and moderate intensity activities, like football, tend to produce more stabilised glucose levels during the activity5,10-13. For example, Figure 1 below illustrates the average change in blood glucose levels during 45-minutes of a simulated match in people with type 1 diabetes. Compared with running (red trace), a simulated first half of football (blue trace) tends to, on average, induce a lower drop in blood glucose levels even when the total amount of energy used (termed energy expenditure) is similar5. Note however, the long bars that stretch above and beyond each data point – this illustrates the amount of variability around the mean response; in other words, it demonstrates how much people can vary in their response to the average…. It’s quite a bit!
Figure 1. The impact of different types of exercise on blood glucose levels during and immediately after a simulated first half of football running (blue trace) and continuous running (red trace) in people with type 1 diabetes. Hashed area indicates exercise period. Figure reproduced from Campbell at al14.
Ok, but how are glucose levels maintained or even increased during football?
Although insulin is a very important hormone for blood glucose regulation, other hormones also play important roles. Intense activity produces a marked increase in the release of stress-hormones9, like adrenaline, noradrenaline and cortisol which can help preserve (or even increase) glucose levels during, and for a short-time after, exercise. This is illustrated in Figure 2 where cortisol levels were shown to be elevated in response to 45-minutes of a simulated match (blue trace) compared to continuous running (red trace) in people with type 1 diabetes. Cortisol – which is produced and released by the adrenal glands on top of the kidney – as well as adrenaline, is also partly responsible for those glucose rises that you might see with pre-match nerves or a poor night’s sleep15.
Figure 2. The impact of different types of exercise on blood cortisol levels during and immediately after a simulated first half of football running (blue trace) and continuous running (red trace) in people with type 1 diabetes. Hashed area indicates exercise period. Figure reproduced from Campbell at al14.
How do stress hormones increase glucose?
These stress-hormones stimulate the body to break down stored glycogen into glucose2. In the muscle, glycogen broken down into glucose is simply converted into energy because this tissue lacks a special enzyme that prevents glucose being released into the blood. The culprit for increased blood glucose levels is the liver. Unlike muscle, the liver has a special enzyme that enables the conversion of glycogen to glucose for release into the blood. With high levels of stress hormones circulating, the liver is stimulated to increase its release of stored glucose2. In contrast to football, continuous moderate-intensity activity achieves only achieves a modest increase in stress-hormones5 meaning that they have only a minor impact on glucose levels.
How long will the effects of stress hormones last?
Although these hormones can have dramatic effects on blood glucose levels, they are usually very short lasting – for example, adrenaline is usually cleared from the blood within 5-10 minutes16. Importantly however, the hormonal and metabolic responses during repeated intense bouts are additive when recovery intervals are short17. This means that in a typical football match (especially those that are physically demanding, and for certain positions like wingers or attacking wingbacks) that there is likely insufficient time for full clearance of these hormones from the circulation before the next high-intensity bout. This means that you could see a gradual rise in glucose levels over each playing half.
How long will it take my glucose levels to normalise after football?
Hormones act for a relatively short time meaning that once levels drop, their influence on glucose levels will also be short-lasting. Although football might confer a lower risk of hypoglycaemia during and immediately afterwards, there is still an increased risk of developing hypoglycaemia later after exercise, so much so that the risk of developing late-onset hypoglycaemia seems to be comparable to other forms of exercise like running or lifting weights5. Read our other article to learn more about post-exercise hypoglycaemia and how to avoid it.
Are there other factors that can affect blood glucose levels during exercise?
Yes. Lots. Of course, with all aspects of type 1 diabetes, blood glucose responses to any form of exercise will to some extent vary from person to person, and from match to match. Your own physical fitness, technical ability, playing position, tactical role, style of playing, as well as ball possession of the team, quality of the opponent, importance of the game, seasonal period, playing surface, and environmental factors like humidity and temperature18 (to name but a few) will all influence both performance and diabetes management. As such, careful planning of training, nutrition, and insulin dosing strategies are required in preparation for training and match days in optimise performance and manage diabetes effectively and safely.
Matthew is an internationally recognised research scientist specialising in exercise, diet, and type 1 diabetes. He also provides consultancy and diabetes coaching to people living with type 1 diabetes and those that support them.
Matthew has a PhD in nutrition and exercise metabolism, is author to over 150 research publications and holds honorary titles with the University of Cambridge and University of Leeds. He is a certified clinical exercise physiologist accredited by the American College of Sports Medicine, a registered nutritionist, and a member of the Institute of Food Science and Technology. He also provides consultancy to professional bodies and professional athletes including NHS England, the World Health Organisation, and TeamGB.
If you are interested in learning how to improve your type 1 diabetes management around exercise, contact Matthew at: firstname.lastname@example.org
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