In part 1 of this series  we discussed some of the challenges and barriers to exercise in type 1 diabetes. Now in part 2, Dr Kate Marsh focuses on what appears to be the major challenge for people with type 1 diabetes  – reducing the risk of exercise-related hypoglycaemia.

There’s more than one way

The most common recommendations for maintaining blood glucose levels during exercise, and reducing the risk of hypoglycemia, are manipulation of insulin doses and/or carbohydrate intake, and timing exercise to avoid periods of peak insulin action. But this isn’t always practical or desirable. What if exercise is unplanned or someone wants to exercise after a meal? What if they are using exercise to help with weight management and don’t want to eat extra food to compensate for the activity?

Furthermore, research shows that these strategies may not be sufficient to prevent all episodes of hypoglycaemia.

A study of 11 male subjects with T1 diabetes, performing 45 minutes of treadmill running found that while a 25% pre-exercise and 50% post-exercise reduction in rapid-acting insulin dose with meals protected against early onset-hypoglycaemia (up to 8 hours after the exercise session), it didn’t protect against late-onset exercise-related hypoglycaemia [1].

The same research group similarly found that inclusion of an evening snack (either high or low glycemic index (GI)) with a reduced rapid-acting insulin dose following evening exercise was able to protect against hypoglycaemia for around 8 hours after exercise, but not against late nocturnal hypoglycaemia [2].

So while adjusting food intake and insulin remain important, of interest is research showing other ways in which the risk of hypos could be reduced, involving manipulation of exercise intensity, type and order. While most of these studies are only small and have been done in healthy, active individuals with type 1 diabetes, they provide a useful starting point for individuals with type 1 to consider when trying to determine the impact of exercise on their blood glucose levels.

Up the intensity

Professor Paul Fournier, Professor of Exercise Physiology and Biochemistry at the University of Western Australia (UWA) School of Sport Science, Exercise and Health, and colleagues have looked at the effect of intermittent high intensity exercise and a short maximal sprint on blood glucose levels and reducing hypoglycemia risk. Perhaps opposite to what you might think, they have shown that incorporating high intensity exercise can reduce the risk of exercise-related hypoglycaemia.

In their first study, comparing 20 minutes of high intensity interval training (continuous moderate activity with 4 second maximal sprints every 2 minutes), blood glucose levels declined more rapidly during the first 15 minutes compared to a control (rest) group but remained stable during the subsequent hour of recovery while continuing to decline in the control group [3].

In a second study it was found that 30 minutes of intermittent high intensity exercise (as per the first study) compared to exercising continuously at a moderate pace, resulted in smaller drop in blood glucose levels in a group of seven healthy individuals with type 1[4].

Both exercise trials were performed after breakfast, with the subjects taking their usual morning insulin dose and eating their usual breakfast, without any adjustments to food or insulin doses to accommodate the exercise.

These findings were confirmed by Swiss researchers who recently published a paper showing reduced glucose requirements with intermittent high intensity versus continuous exercise, with more than 50% less glucose needed to maintain euglycemia in the last 30 minutes of exercise in 12 males with well-controlled T1 diabetes.

In this study, subjects again had their usual breakfast and insulin doses without adjustment for exercise, although this time exercise was commenced a number of hours after breakfast, when insulin levels would have been lower [5].

Professor Fournier and colleagues have also shown that doing a maximal sprint for just 10 seconds at the end of a moderate intensity exercise session can reduce the risk of hypoglycaemia for up to 2 hours after exercise[6]. This was associated with elevated levels of catecholamines, growth hormone, and cortisol [6].

They also found that a similar maximal sprint prior to moderate intensity exercise reduced the fall in blood glucose levels during early recovery (in the 45 minutes following exercise) but not during the exercise itself or in later recovery [7]. In these studies exercise was commenced around 2 hours after subjects ate a standard breakfast and took their regular rapid-acting insulin dose.

While they conclude that the addition of a sprint after moderate-intensity exercise provides another means to reduce the risk of hypoglycemia in active individuals with type 1 diabetes, Professor Fournier points out that this isn’t for everyone.

“This isn’t suitable option for all individuals – for example, the elderly, those with complications and obese individuals”, he told the limbic. He is also unsure about using it with younger children.

Exercise physiologist, Allan Bolton agrees. “A maximal sprint means ‘all-out’ and is clearly not practical in a musculoskeletal sense for many individuals”.

Lift then run

Considering the type and order of exercise performed might also be important when it comes to preventing hypos.

In a study of 12 physically active individuals with type 1 diabetes, Canadian researchers found that resistance training didn’t lower blood glucose levels as much during exercise, compared to aerobic exercise, and resulted in more stable and prolonged reductions in blood glucose levels after exercise[8].

When they combined aerobic and resistance training in the one session, they found that doing resistance training before aerobic exercise resulted in more stable blood glucose levels throughout the exercise session and reduced the risk of post-exercise hypoglycaemia [9].

Type and timing matters

For those who prefer to exercise first thing in the morning, without eating, a UK study of 8 individuals with type 1 diabetes is of interest. They found that a morning resistance training session after an overnight fast with the normal basal insulin dose but omission of pre-exercise rapid-acting insulin didn’t result in acute post-exercise hypoglycaemia. In fact, BGLs rose for at least an hour after one or two sets of exercise, but returned to pre-exercise levels after a third set [10].

Preventing hypos – how much carbohydrate is really needed?

“There isn’t a lot of research in this area” Dr Vinutha Shetty, a Paediatric Endocrinologist and PhD researcher at the University of Western Australia told the limbic. She suspects that current guidelines may overestimate carbohydrate needs for exercise, particularly high intensity activity, and her first study supports this.

Published earlier this year her study of nine recreationally active individuals with type 1 diabetes (2 adolescents and 7 adults) found that surprisingly little glucose was needed to prevent hypoglycemia at basal insulin levels [11]. The average glucose required was 2g/hour at the lowest exercise intensity (35% VO_2peak) and around 4g/hour at moderate intensities (50 and 65% VO_2peak), although there was considerable variation between participants (ranging from 0-15g/hour). At high intensity (85% VO_2peak) no glucose was needed by any of the participants. And a few participants needed no glucose at any exercise intensity.

“However this was using IV glucose so isn’t totally relatable to the clinical setting” Dr Shetty explained. “These findings need to be translated to oral intake”, she says, noting that this is the subject of her next study.

She is also repeating the study at higher insulin levels (to simulate post-meal levels), expecting that larger amounts of glucose will be needed to maintain euglycemia compared to exercising with only basal insulin on board.

The bottom line

Exercise-related hypoglycaemia is common and can be a significant barrier to exercise in many people with type 1 diabetes. Research is showing us that there are many ways to reduce the risk of hypos with exercise – the ongoing challenge is finding a way to not only prevent hypos during exercise, but also for many hours afterwards, while at the same time avoiding hyperglycemia.

Related article: Exercise and type 1 diabetes – a difficult balancing act

References

1. Campbell, M.D., et al., Large Pre- and Postexercise Rapid-Acting Insulin Reductions Preserves Glycemia and Prevents Early- but Not Late-Onset Hypoglycemia in Patients With Type 1 Diabetes. Diabetes Care, 2013.
2. Campbell, M.D., et al., A low-glycemic index meal and bedtime snack prevents postprandial hyperglycemia and associated rises in inflammatory markers, providing protection from early but not late nocturnal hypoglycemia following evening exercise in type 1 diabetes. Diabetes Care., 2014. 37(7): p. 1845-53. doi: 10.2337/dc14-0186. Epub 2014 May 1.
3. Guelfi, K.J., T.W. Jones, and P.A. Fournier, Intermittent high-intensity exercise does not increase the risk of early postexercise hypoglycemia in individuals with type 1 diabetes. Diabetes Care., 2005. 28(2): p. 416-8.
4. Guelfi, K.J., T.W. Jones, and P.A. Fournier, The Decline in Blood Glucose Levels Is Less With Intermittent High-Intensity Compared With Moderate Exercise in Individuals With Type 1 Diabetes. Diabetes Care, 2005. 28(6): p. 1289-1294.
5. Bally, L., et al., Metabolic and hormonal response to intermittent high-intensity and continuous moderate intensity exercise in individuals with type 1 diabetes: a randomised crossover study. Diabetologia., 2016. 59(4): p. 776-84. doi: 10.1007/s00125-015-3854-7. Epub 2016 Jan 6.
6. Bussau, V.A., et al., The 10-s Maximal Sprint: A novel approach to counter an exercise-mediated fall in glycemia in individuals with type 1 diabetes. Diabetes Care, 2006. 29(3): p. 601-606.
7. Bussau, V.A., et al., A 10-s sprint performed prior to moderate-intensity exercise prevents early post-exercise fall in glycaemia in individuals with type 1 diabetes. Diabetologia., 2007. 50(9): p. 1815-8. Epub 2007 Jun 22.
8. Yardley, J.E., et al., Resistance Versus Aerobic Exercise: Acute effects on glycemia in type 1 diabetes. Diabetes Care, 2012.
9. Yardley, J.E., et al., Effects of Performing Resistance Exercise Before Versus After Aerobic Exercise on Glycemia in Type 1 Diabetes. Diabetes Care, 2012. 35(4): p. 669-675.
10. Turner, D., et al., Impact of single and multiple sets of resistance exercise in type 1 diabetes. Scand J Med Sci Sports., 2015. 25(1): p. e99-109. doi: 10.1111/sms.12202. Epub 2014 Mar 20.
11. Shetty, V.B., et al., Effect of Exercise Intensity on Glucose Requirements to Maintain Euglycemia During Exercise in Type 1 Diabetes. J Clin Endocrinol Metab., 2016. 101(3): p. 972-80. doi: 10.1210/jc.2015-4026. Epub 2016 Jan 14.