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Intermittent High-Intensity Exercise: Higher Now, Lower Later?

 
Sheri_ColbergBy Sheri Colberg, PhD

 

In a previous column, we talked about how insulin action is affected by many different factors. The one with the biggest impact is the amount of glycogen stored in skeletal muscles and how that is impacted by regular physical activity. This week, though, we need to discuss the impact of high-intensity exercise and how the resultant glycogen content may impact blood sugars differently over a longer period of time.

It is well established that high-intensity exercise can raise blood glucose levels in people with both types of diabetes, albeit temporarily. Recently published research studied the impact of doing short sprints interspersed during a longer bout of moderate exercise in subjects with Type 1 diabetes. In that case, a higher exercise intensity done intermittently (such as during sports requiring a stop-and-start action like tennis and soccer) allowed for blood glucose levels to be maintained more effectively — and even rise some due to the greater release of glucose-raising hormones — during and for at least two hours following that activity1. You may also remember that doing a 10-second sprint at the end of moderate exercise has a similar ability to maintain blood glucose levels for a couple of hours post-exercise2. What has not been fully researched, though, is what happens to the glycemic balance hours later after participating in such activities. How are blood sugar levels affected by the higher-intensity work (albeit short-lived and intermittent) over the longer term? 

In a very recent study, researchers assessed the glucose responses of patients with Type 1 diabetes during and for 20 hours after completing two different types of exercise using continuous glucose monitoring3. The subjects either underwent 30 min of intermittent high-intensity exercise (IHE) or exclusively moderate-intensity exercise (MOD) on different test days.  While their blood glucose levels declined during both types of exercise, at 150 min following the start of exercise, glucose levels were still slightly higher following IHE.  More interestingly, though, between midnight and 6:00 a.m. their glucose levels were significantly lower after IHE than after moderate exercise, and significantly more subjects experienced hypoglycemia after IHE (7 vs. only 2 after MOD). The researchers concluded that higher intensity exercise, even when intermittent, is associated with delayed nocturnal hypoglycemia.

What is the best advice for your patients then?  Participation in any type of exercise can increase the risk of experiencing severe hypoglycemia during exercise and for up to 31 hours of recovery. This risk can be minimized by adjusting the dosage of insulin and food intake to maintain blood glucose levels within the normal physiological range. However, people must also realize that moderate- and high-intensity exercise may have contrasting effects on blood glucose levels and require different management strategies. Engaging in a combination of moderate- and high-intensity exercise (that is, IHE), which is the type of activity characteristic of most team and field sports (and spontaneous play in children), elicits a unique response and will likely require a different strategy for managing blood glucose levels both during and afterwards, with a greater focus on preventing delayed hypoglycemia. 

References:
  1. Guelfi KJ, Ratnam N, Smythe GA, Jones TW, Fournier PA. Effect of intermittent high-intensity compared with continuous moderate exercise on glucose production and utilization in individuals with type 1 diabetes. Am J Physiol Endocrinol Metab. 2007;292(3):E865-70. 
  2. Bussau VA, Ferreira LD, Jones TW, Fournier PA. 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):601-6. 
  3. Maran A, Pavan P, Bonsembiante B, Brugin E, Ermolao A, Avogaro A, Zaccaria M. Continuous glucose monitoring reveals delayed nocturnal hypoglycemia after intermittent high-intensity exercise in nontrained patients with type 1 diabetes. Diabetes Technol Ther. 2010 August 31 [Epub ahead of print]
To sign up for 5 free healthy living reports via e-mail, visit www.lifelongexercise.com. For more information on exercise and physical activity in general, also check out my web site at www.shericolberg.com. If you need tips for getting started on an exercise/lifestyle program, consult The 7 Step Diabetes Fitness Plan. People with any type of diabetes who are already more active may benefit from reading the Diabetic Athlete’s Handbook.
 

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