Yes, it would be reasonable to wait for a period of time after the patient is administered insulin before commencing exercise.
In order to preserve central nervous system function, blood glucose levels are remarkably well maintained during physical activity. Hypoglycemia during physical activity rarely occurs in non-diabetic individuals. The metabolic adjustments that preserve normoglycemia during physical activity are in large part hormonally mediated. These hormonal adaptations are essentially lost in insulin-deficient patients with Type 1 diabetes. As a consequence, when such individuals have too little insulin in their circulation due to inadequate therapy, an excessive release of counter-insulin hormones during physical activity may increase already high levels of glucose and ketone bodies and can even precipitate diabetic ketoacidosis. Conversely, the presence of high levels of insulin, due to exogenous insulin administration, can attenuate or even prevent the increased mobilization of glucose and other substrates induced by physical activity, and hypoglycemia may ensue.
Similar concerns exist in patients with Type 2 diabetes on insulin or sulfonylurea therapy; however, in general, hypoglycemia during physical activity tends to be less of a problem in this population. Indeed, in patients with Type 2 diabetes, physical activity may improve insulin sensitivity and assist in diminishing elevated blood glucose levels into the normal range.
All levels of physical activity, including leisure activities, recreational sports and competitive professional performance, can be performed by people with Type 1 diabetes who do not have complications and are in good blood glucose control. However, hypoglycemia, which can occur during, immediately after, or many hours after physical activity, can be avoided.
Some general guidelines that may help in regulating the glycemic response to physical activity include:
1. Metabolic control before physical activity
- If possible, test the patient’s blood glucose before, during and after the activity to monitor blood glucose levels. This is important when beginning or changing an exercise program. Avoid physical activity if fasting glucose levels are >250 mg/dl and ketosis is present, and use caution if glucose levels are >300 mg/dl and no ketosis is present.
- When insulin is peaking, exercise isn’t recommended as it may lead to low blood glucose. Before exercise, have the patient take less insulin or eat more food at mealtime or as a snack. Have the patient ingest added carbohydrate if glucose levels are <100 mg/dl.
2. Blood glucose monitoring before and after physical activity
- Identify when changes in insulin or food intake are necessary.
- Learn the glycemic response to different physical activity conditions.
- Also, it is recommended that the patient avoids injecting insulin into arms and legs. An abdominal injection site may help lower the risk for hypoglycemia associated with exercise.
3. Food intake
- Ideally, if the patient is taking insulin and knows ahead of time when exercise will commence, then the rapid or short insulin meal dose may be decreased before the activity instead of taking extra food during the activity. However, the patient may consume added carbohydrate as needed to avoid hypoglycemia.
- Carbohydrate-based foods should be readily available during and after physical activity.
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