There are many reasons for individuals with type 1 diabetes to exercise. Regular exercise in this population has been shown to improve insulin sensitivity, increase fitness, improve body composition, reduce cardiovascular disease risk, reduce mortality, and result in greater well-being 1, 2.
However, unlike in type 2 diabetes, exercise doesn’t necessarily improve glycemic control in those with type 13. On the contrary, exercise can sometimes make it more difficult to control blood glucose levels by adding another variable to what is often already a difficult balancing act. This may explain why studies have found that many people with type 1 diabetes don’t exercise regularly 4.
Exercise and type 1 diabetes – a difficult balancing act
Exercise increases the muscular demand for glucose. In the person without diabetes, this increase in glucose uptake by the exercising muscles is closely matched by increased hepatic glucose production (the result of a number of factors including a fall in insulin levels and the release of counter-regulatory hormones), so that blood glucose concentrations remain relatively constant.
In those with type 1 diabetes, however, this finely-tuned process is lost. Insulin concentrations don’t respond to exercise in the normal manner, and the balance between muscle glucose utilisation and hepatic glucose production may be disturbed5.
As a result, exercise has the potential to lead to hypoglycemia and/or hyperglycemia depending on a number of different factors, including the intensity and duration of exercise, the timing of exercise in relation to insulin and meals, and the type of exercise being performed.
Exercise-related hypoglycemia is a risk because individuals with type 1 diabetes don’t experience a fall in plasma insulin levels with exercise. The increased uptake of glucose by the exercising muscles together with elevated insulin levels, which inhibit hepatic glucose production, can result in rapid decreases in blood glucose levels, possibly resulting in hypoglycemia 5.
Exercise also increases insulin sensitivity, an effect which can last up to 24 hours after an exercise session, particularly with higher intensity, longer duration exercise.
Exercise-induced hyperglycaemia is also a possibility, and may occur if exercise is performed when insulin levels are insufficient. A lack of insulin prevents the exercising muscle cells receiving glucose and stimulates the action of glucagon to increase hepatic glucose production5. This results in an increase in the blood glucose level, and the exercising muscle is unable to use this fuel. Continued exercise under these conditions can increase lipolysis (as muscle cells metabolise fats as an alternative fuel), leading to the development of ketones and a further increase blood glucose levels.
High intensity activities, which cause a greater release of counter-regulatory hormones including adrenaline and glucagon, can also cause both immediate and sustained elevations in blood glucose levels.
Exercise-related hypoglycemia – a common problem
While the risks of hypoglycemia with exercise are well-understood and strategies to reduce this risk have been identified, it nevertheless remains a frequent problem for many people.
In a recent online survey of 502 adults with type 1 diabetes, 70% reported experiencing low blood glucose levels after exercise despite often making adjustments to their carbohydrate intake and insulin doses prior to and following exercise 6.
Similarly, in a recently published study of 51 children with type 1 treated with either MDI or CSII, the use of blinded CGM identified frequent episodes of nocturnal hypoglycemia following exercise 7.
Daytime physical activity (measured by accelerometry) was strongly associated with hypoglycemia risk – 1 hour of moderate to vigorous physical activity increased the risk of hypoglycemia by 58% and vigorous physical activity increased the risk by 82%. Of particular concern was that most episodes were asymptomatic and many were prolonged (30% lasting over 3 hours and 34% between 1-3 hours).
Multiple factors at play
A number of different factors can determine the glycemic response to exercise in type 1 diabetes including the type of exercise, intensity and duration of exercise, the timing of exercise, the individuals insulin regimen, circulating insulin levels during exercise, blood glucose levels prior to exercise, nutritional status and food intake prior to and during exercise, fitness level, the stress of competition and environmental factors such as the temperature, humidity and altitude during exercise.
This can make predicting the response to exercise and adjusting treatment to avoid hypo and hyperglycaemia difficult. It’s not surprising, then, that many individuals with type 1 diabetes report that exercise makes their BG levels harder to control and that they feel less able to predict their BG levels while exercising 6.
“There are so many questions” Professor Paul Fournier, Professor of Exercise Physiology and Biochemistry at the University of Western Australia (UWA) School of Sport Science, Exercise and Health, told the limbic.
“A major factor is hypos, but also not going too high” he said. “That’s the basis of our work – to help people stay in that narrow band. It’s pretty challenging”. His research group have looked at the impact of high intensity exercise and more recently, how much glucose is needed during exercise to prevent hypoglycemia. We will look at some of the findings of his research in part 2 of this series.
Identifying and addressing barriers
Is this ‘challenge’ of maintaining stable glycemic control during exercise preventing people with diabetes from being active? It seems that both diabetes-specific factors and factors common to the general population can stop those with type 1 being more active.
A study of 100 adults with diabetes found fear of hypoglycemia to be the greatest barrier to exercise, followed by work schedule, loss of control over diabetes and low levels of fitness 4. Having an understanding of insulin pharmacokinetics, implementation of strategies to reduce the risk of exercise-related hypos, social support and having someone to exercise with were associated with fewer barriers.
In the online survey of 502 adults with type 1 diabetes, participants reported that exercise makes their blood glucose levels harder to control and makes them feel less able to predict their blood glucose levels while exercising 6. They also agreed that fear of hypos is one factor which keeps them from exercising.
A qualitative study of 26 individuals with longstanding type 1 diabetes identified six main barriers to exercise – lack of time and work related factors, access to facilities, lack of motivation, embarrassment and body image, weather, and diabetes specific barriers (low levels of knowledge about managing diabetes and its complications around exercise) 8. Being given advice and encouragement around managing diabetes for exercise was identified as an important facilitator of exercise.
Allan Bolton, an Accredited Exercise Physiologist specialising in type 1 diabetes, creator and founder of the exT1D program agrees. A keen sportsman who has lived with type 1 diabetes for 38 years, he identified a real need for more comprehensive information and education for individuals with type 1 who want to be active.
“I couldn’t find anything like this program out there, that’s why I built it” he told the limbic. “It provides something that helps answer all the questions I’ve had and more”, he added. His online program is aimed at educating and empowering individuals with type 1 diabetes so they can participate in regular physical activity, exercise and sport with confidence.
While Allan knew his course was effective from the feedback he has received from participants, the program has recently undergone scientific scrutiny, with researchers from Sydney University Medical School conducting a randomised controlled trial with 32 subjects with type 1 diabetes.
Completing the online program was found to significantly reduce the incidence and duration of exercise-related hypoglycaemia, particularly in those were having the most hypos associated with exercise. Participants also reported increased confidence in preventing exercise-related hypos and experienced significant reductions in self-reported fear of hypos.
Part 2 of this article will focus on strategies for reducing the risk of exercise-related hypoglycemia – a major barrier to exercise in those with type 1.
- Chimen, M., et al., What are the health benefits of physical activity in type 1 diabetes mellitus? A literature review. Diabetologia., 2012. 55(3): p. 542-51. doi: 10.1007/s00125-011-2403-2. Epub 2011 Dec 22.
- Bohn, B., et al., Impact of Physical Activity on Glycemic Control and Prevalence of Cardiovascular Risk Factors in Adults With Type 1 Diabetes: A Cross-sectional Multicenter Study of 18,028 Patients. Diabetes Care., 2015. 38(8): p. 1536-43. doi: 10.2337/dc15-0030. Epub 2015 May 26.
- Kennedy, A., et al., Does exercise improve glycaemic control in type 1 diabetes? A systematic review and meta-analysis. PLoS One., 2013. 8(3): p. e58861. doi: 10.1371/journal.pone.0058861. Epub 2013 Mar 15.
- Brazeau, A.S., et al., Barriers to physical activity among patients with type 1 diabetes. Diabetes Care., 2008. 31(11): p. 2108-9. doi: 10.2337/dc08-0720. Epub 2008 Aug 8.
- Wasserman, D.H. and B. Zinman, Exercise in Individuals With IDDM. Diabetes Care, 1994. 17(8): p. 924-937.
- Pinsker, J.E., et al., Techniques for Exercise Preparation and Management in Adults with Type 1 Diabetes. Can J Diabetes, 2016. 17(16): p. 30018-1.
- Bachmann, S., et al., Nocturnal Hypoglycemia and Physical Activity in Children With Diabetes: New Insights by Continuous Glucose Monitoring and Accelerometry. Diabetes Care., 2016. 39(7): p. e95-6. doi: 10.2337/dc16-0411. Epub 2016 May 13.
- Lascar, N., et al., Attitudes and barriers to exercise in adults with type 1 diabetes (T1DM) and how best to address them: a qualitative study. PLoS One., 2014. 9(9): p. e108019. doi: 10.1371/journal.pone.0108019. eCollection 2014.