by Jean-Jacques Grimm
Exercise can cause a rise in blood glucose in two situations when…
(1) when an individual is insulin-deficient and metabolically unstable; (2) with extremely intense exercise in individuals who have well controlled diabetes….
This situation is the consequence of a severe deficit in circulating insulin, leading to an increase in hepatic glucose production, a decrease in glucose disposal by muscle, and the production of ketones. Furthermore, exercise stimulates the secretion of counter-regulatory hormones (glucagon, catecholamines, growth hormone and cortisol), all of which contribute to hyperglycemia and metabolic deterioration.30
Hyperglycemia (>14.0 mmol l-1) with ketonuria is an absolute contraindication to exercise. The metabolic imbalance must be corrected by short-acting insulin injections and the activity must not be resumed until the blood glucose level starts to decrease and urine ketones disappear.
That situation may be the consequence of a mild and relative insulin deficiency. It can be the result of an excess of carbohydrate at the last meal or snack or the consequence of stress. Exercise is allowed but with caution. Good hydration must be stressed (drink before, during and after exercise). A blood glucose measurement is recommended after 30 min of exercise. If no decrease is observed, exercise cessation is recommended and a correction insulin injection as well.
Very intense short exercise with normal blood glucose
Very intense [>80 per cent of maximal oxygen uptake (V02max)] and short-duration exercise, such as weight-lifting, can increase glycemia. The main explanation is a large increase in catecholamine production.16 In the original work of Mitchell et al., 15 the duration of the effort was 10 min and the intensity 80 per cent of the V02max. Two groups of diabetics were observed, a metabolically well-controlled group (mean blood glucose 86mg/dL. or 4.8 mmol l-1), and a less well- controlled group (mean blood glucose 149mg/dL.or 8.3 mmoll-J). Two hours after exercise, the increase in blood glucose was 52mg/dL. or 2.9 mmoll-1 in the well-controlled group and 76mg/dL.or 4.2 mmoll-J in the less well-controlled group.
When short bouts of intense exercise are repeated many times during a limited time span (1-2 h) such as, for example, during an ice hockey game, energy consumption is considerable, and will finally lead to a decrease in blood glucose, with a risk of hypoglycemia.
Two important principles must be taken into account in making treatment adjustments before, during and after exercise in people with type 1 diabetes:
Figure 2.3 Effect of subcutaneously injected insulin at rest (•) and with muscular exercise (0)28
- Exercise is always associated with extra energy consumption.
- Exercise stimulates glucose uptake into muscle cells (increases insulin sensitivity). The same amount of insulin allows more glucose to be metabolized during an effort than at rest (Figure 2.3).
Most people with type 1 diabetes who are planning to exercise have heard about extra carbohydrates and insulin dose adjustments and are aware of the increased risk of hypoglycemia. However, experience shows that very often they underestimate the reduction in insulin dose required. In addition to this, the need to compensate for energy expenditure with extra carbohydrate is often neglected or underestimated. This is the main cause of preventable hypoglycemia.33.34
These errors become critical when, due to an excess of circulating insulin hepatic glycogen stores cannot be mobilized and gluconeogenesis cannot occur. (See Figure 2.2).
Correct preparation for exercise needs a detailed assessment of all the characteristics of the effort: duration, intensity, time from last meal and or insulin injection, time of the day and insulin activity (blood insulin level) during the exercise session. Frequent blood glucose testing is of value during the first attempts in any new activity.
- Leaving an interval of 2-3 h between the last meal/insulin injection avoids exercising during the peak insulin action where the risk of hypo glycemia is high.35 This is valid with short-acting insulin analogues. With classical short-acting insulin’s it is recommended to wait 4 h or substantially decrease the meal insulin dose.
- Time of day is important, not only because insulin levels fluctuate through the day but also because the body’s need for insulin is low at certain times of the day (Figure 2.4).
- Estimation of the times when insulin levels are high for every type of insulin injection is one of the important homework tasks for the would-be exerciser.37 Table 2.1 shows ‘intense’ insulin activity periods for different insulin preparations and dosages. Exercising during these periods needs special attention because of the increased risk of hypoglycemia. When exercise is supposed to take place during the ‘intense’ activity of a short-acting insulin, its dose must be drastically reduced and extra carbohydrates taken too.
Figure 2.4 Variations of the hourly insulin needs during 24 h, independently of meals, in 198 subjects with type 1 diabetes treated by continuous subcutaneous insulin infusion pump therapy
15.Mitchell TH, Abraham G. Schiffrin A. Leiter LA, Marliss EB. Hyperglycemia after intense exercise in IDDM subjects during continuous subcutaneous insulin infusion: Diabet. Care 1988; 11: 311-317.
16.Purdon C, Brousson M, Nyreen SL et al. The roles of insulin and catecholamines in the glucoregulatory response during intense exercise and early recovery in insulin-dependent diabetic and control subjects. 1. Clin. Endocinol. Me tab. 1993; 76: 566-573.
30. Sonnenberg GE. Kemmer F\V. Berger M. Exercise in type 1 (insulin-dependent) diabetic patients treated with continuous subcutaneous insulin infusion: prevention of exercise-induced hypoglycemia. Diabetologia 1990: 33: 696-703.
32.Berger M, Berchtold P, Cuipers HJ et al. Metabolic and hormonal effects of muscular exercise in juvenile type diabetes. Diabetologia 1977; 13: 355-365.
33.Grimm Ll, Golay A, Habicht F, Berne C, Muchnick, S. Prevention of hypo glycemia during exercise: more carbohydrate or less insulin? Diabetes 1996; 45(suppl.): 104A (abstract).
34.Grimm Jl. Ybarra J, Berne C, Muchnick S, Golay A. A new table for prevention of hypoglycemia during physical activity in type 1 diabetic patients. Diabet Metab. 2004; 30: 465-470.
36.Austernat E, Stahl T. Insulinpumppentherapie. Berlin: de Gruyter, 1989.
37.Berger W, Grimm n. Insulinotherapie. Comment gerer all quotidien les variations physiologiques des besoins en insuline. Paris: Masson, 1999.
The new edition of this acclaimed title provides a practical guide to the risks and benefits of undertaking sport and general exercise for patients with diabetes.
Fully updated to reflect the progress and understanding in the field, the book features new chapters and material on insulin pump therapy and exercise, physical activity and prevention of type 2 diabetes, dietary advice for exercise and sport in type 1 diabetes, and fluid and electrolyte replacement.
Next week: New Joslin Diabetes Deskbook excerpt
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