Our first article is on Diabetes and Exercise and was written by Mr. Andrew Heilbrunn, our Head Biokineticist.
Safety first – managing your blood glucose whilst exercising
Mr. Andrew Heilbrunn
Biokinetics Department, Centre for Diabetes and Endocrinology, Houghton, Johannesburg
In the last five decades, there have been numerous diabetes and exercise related research. The majority of researchers believe that the majority of patients would benefit significantly from regular activity.
Physically active people with diabetes may live longer and have far lower rates of heart disease. Regular activity may help reduce the risk of diabetes related complications such as neuropathy and nephropathy, and may enhance quality of life, reduce stress, anxiety and depression.
How does exercise improve blood glucose control?
There are numerous theories as to how exercise may improve blood glucose control, however the most convincing theory is muscle and liver glycogen replenishment following exercise. During exercise, the body will utilize blood glucose and liver and muscle glycogen (stored glucose) as an energy source. Following exercise, the liver and muscle cells will draw glucose out of blood to replenish the glycogen stores that were used while you were exercising. By drawing blood glucose out of the blood after exercise, the blood glucose levels drop, hence improving ones control.
In the majority of cases exercise will improve blood glucose control, however in certain cases where patients are insulin requiring, exercise may worsen control, unless people adjust their insulin dosages and take the correct snack at the correct time.
The blood glucose response to exercise in people with Type 1 diabetes in particular is not always predictable. However a good understanding of the potential blood glucose response to exercise and the action of insulin and its administration, will aid patients and therapists in making the correct, safe diabetes management decisions.
The aim of insulin adjustments pre and post exercise is to:
§ Improve blood glucose control;
§ Create a stable blood glucose level for optimum exercise performance;
§ Mimic the normal hormonal action of insulin during exercise as observed in the person without diabetes;
§ Prevent hypoglycaemia during and after activity.
Generally, there are three scenarios. If there is sufficient circulating insulin, when you take your correct dose, exercise may lead to a decrease in blood glucose levels and insulin requirements for up to 24 hours. If circulating insulin levels are high, exercise may lead to a hypoglycaemia reaction (low blood glucose). If circulating insulin levels are low, exercise may lead to hyperglycaemia (high blood glucose) and possibly ketoacidosis.
When is the safest time to exercise?
Current research suggests that whilst taking multiple daily injections the most favourable times to exercise are before breakfast and before dinner (fasting state). The reason for this suggestion is that the active patient is less likely to become hypoglycaemic (low blood glucose) at these times. If a patient exercises in the post-meal state during the peak effect of insulin, the blood glucose lowering effect of exercise may be unpredictable. Therefore it is suggested that when a person exercises 1 to 3 hours post-meal, they ingest 1 gram of carbohydrate per kilogram of body weight during exercise in order to prevent hypoglycemia.
Hypoglycaemia
Research and findings: Exercise performed late in the day (i.e. after school or work) may lead to hypoglycaemia which may be unnoticed during sleep in the majority of individuals. In children and adolescents there may be as high as a 26% incidence of hypoglycaemia on exercise nights. If you exercise for more than 45 minutes in the afternoon, it is suggested that you decrease your insulin dosage.
The Patient with Type 1 Diabetes should pay attention to their precise blood glucose level prior to exercise:
§ If the blood glucose levels are 6 mmol/l or lower before exercise, one should take a substantial snack before exercising (E.g. Peanut butter sandwich).
§ If the blood glucose levels are between 7 and 10 mmol/l, only take a small snack (E.g. banana).
§ If the blood glucose levels are greater than 15 mmol/l, check for ketones in the blood or urine. If there are no ketones, exercise should be safe and would probably be beneficial. If ketones are present, do not exercise. Exercise will probably exacerbate the ketotic state. Eliminate the ketones first before continuing with exercise.
Post exercise snacks and insulin adjustments to prevent post exercise hypoglycaemia
The key to good glycaemic control is strategic carbohydrate replenishment and insulin lowering post exercise. If one has exercised at a high intensity for more than 45 minutes, it is imperative to take the necessary snacks before going to bed and / or to decrease the insulin dosage strategically over the next 24 hours.
Conclusion
If people that are insulin-requiring exercise on a regular basis, it is imperative to balance your insulin dosage and your snacks and your timing of exercise in order to get the best blood glucose control. This is an ongoing process and may require dedication and constant monitoring of blood glucose in a diary. At the Centre for Diabetes and Endocrinology we have highly trained Educators and Biokineticists that can help you in this regard.
What strategies should we employ to prevent hypoglycaemia during and post exercise?
Altered carbohydrate intake and insulin modification tables for both aerobic and anaerobic exercise are available. However, there are additional factors, which may influence blood glucose levels, such as:
§ Type of insulin injected, in particular time of peak action;
§ Injection site;
§ Hydration levels;
§ Heat / cold;
§ Previous hypoglycaemic episode;
§ Previous exercise duration and intensity;
§ Mode of exercise.
Current research suggests that endurance type activities lead to a decrease in blood glucose levels during exercise and for several hours post exercise. Furthermore higher intensity resistance or interval type exercises may initially raise blood glucose levels due to an adrenal response and then blood glucose levels would decrease for several hours post exercise.
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