Exercise Prescription for Diabetes

When I cared for stroke patients in the hospital, diabetes was one of the most common chronic conditions among them. A few managed their blood sugar well, but most did not, raising the risk of complications. Persistently high blood sugar increases the risk of complications including myocardial infarction, heart failure, cerebrovascular accident, hypertension, kidney disease, dyslipidemia, and disorders of the eyes and nerves.

Insulin is a hormone the pancreas produces after food is eaten and blood sugar rises. It promotes the uptake of glucose by muscle, fat, and other cells; if insulin secretion is abnormal, blood sugar levels can exceed the normal range.

The original article was published in the Common Health column

What is diabetes

It means the pancreas cannot supply enough insulin to lower blood sugar. In the earliest days, diabetes was diagnosed by tasting a patient’s urine. Today, the four main categories of diabetes are type 1, type 2, gestational diabetes, and other specific causes; type 2 accounts for about 90% and type 1 for about 5-10%.

Insulin treatment for people with diabetes was developed by the Canadian physician Banting in the 1920s. His team used insulin from animals to improve high blood sugar in dogs and humans, and pharmaceutical companies later carried out related research and production. The distinction between the different types was described in 1935 by a physician named Himsworth.

Type 1 diabetes is caused by autoimmune destruction of the insulin-secreting pancreatic beta cells, so there is a complete lack of insulin, and injection treatment is needed to avoid high blood sugar. Type 2 diabetes is caused by insulin resistance in skeletal muscle, fat tissue, and other cells, combined with a defect in insulin secretion. Type 2 diabetes in particular is related to excess body fat, commonly with abdominal fat or a central-obesity body shape; statistically, people with a BMI over 35 have up to a 30 times higher risk of later developing type 2 diabetes compared with those with a BMI under 23.

Diagnosing diabetes requires measuring blood sugar. The blood glucose meters commonly used today were developed around 1970 and have been a great help in the lives of many people with diabetes. In recent years these meters have kept improving, and some no longer require a finger prick to check blood sugar; they can also connect to a phone to provide the current blood sugar reading at any time.

Glycated hemoglobin (HbA1c) reflects the average blood sugar control over the past 2-3 months. Diabetes societies around the world and the WHO all use an HbA1c of 6.5% or higher as a diagnostic criterion for diabetes; other common criteria are a fasting blood glucose of 126 mg/dL or higher, or a random blood glucose above 200 mg/dL when there are symptoms or an acute presentation of high blood sugar.

Treatment of diabetes

The goal of diabetes treatment is blood sugar control, mainly through diet, exercise, and medication.

The medication treatment of diabetes centers mainly on first-line metformin and other second-line agents. A single agent lowers HbA1c by about 0.7-1.0%; if HbA1c is higher, combination therapy is recommended. The Diabetes Association of the R.O.C. (Taiwan) provides plenty of useful material.

According to research, regular exercise has been shown to improve glucose tolerance, increase insulin sensitivity, and reduce HbA1c. Exercise strengthens insulin sensitivity and has a dose-response relationship (meaning the more exercise, the greater the improvement). Whether type 1, type 2, or prediabetes, patients can improve blood sugar control, reduce the need for medication or insulin injections, and slow the risk factors for later complications.

Pre-exercise assessment

The main goal is to assess whether there are currently acute or chronic complications from high blood sugar, blood pressure, blood sugar monitoring records, the types of medication and timing of doses, past exercise experience, nutritional status, and other chronic conditions. Exercise timing should as far as possible avoid the point of peak insulin action; people who inject insulin daily are advised to exercise daily, because exercising only occasionally tends to lead to unstable blood sugar.

Exercise prescription

Before starting low- to moderate-intensity exercise, people with diabetes and asymptomatic, low-risk people with prediabetes usually do not need exercise testing. Before starting vigorous exercise, higher-risk groups need to consider an electrocardiogram and a full medical evaluation.

Because many people with diabetes have several coexisting chronic conditions, the exercise prescription is recommended to be tailored to the individual. Individualized exercise monitoring and prescription can reduce the risks from blood sugar changes before, during, and after exercise. Current research on exercise training suggests that both resistance and aerobic exercise help with cardiovascular risk in people with type 2 diabetes; some patients have silent cardiac ischemia, and radioisotope scanning to detect areas of cardiac ischemia may be recommended.

Center training on rhythmic large-muscle-group exercise. Aerobic exercise can start at 10 minutes 2-3 times a day and gradually increase to 3-7 days per week at 30 minutes per session, with the goal of reaching 60 minutes per day or per session.

The type of resistance training depends on goals, interests, ability, and the patient’s health status. Resistance training has some contraindications, including uncontrolled hypertension, uncontrolled arrhythmia, aortic dissection, serious cardiac problems, severe proliferative retinopathy, and recent laser surgery. Apart from these contraindications, resistance training is recommended, because in addition to strengthening muscle it helps with insulin action and blood sugar control; current research also supports that combining aerobic and resistance training improves blood sugar control more than either alone.

Because of the effect of collagen glycation on stretching, people with diabetes can develop limited joint range of motion, so stretching exercise is important; proprioceptive and balance training are also recommended.

Precautions during exercise

Before training

• It is recommended to measure blood sugar before and after exercise, especially when just starting or advancing to a new exercise program.
• For patients with autonomic dysfunction whose heart rate and blood pressure responses are blunted, consider using RPE to gauge exercise intensity.
• If pre-exercise blood sugar is under 100 mg/dL, taking in 15 grams of carbohydrate is recommended, with a recheck 10 minutes after intake.
• People with type 1 diabetes should be careful when pre-exercise blood sugar is above 250 mg/dL; testing urine ketones is recommended, and if the level is moderate to high, exercise should be avoided.
• The dose of rapid, short-acting insulin should be reduced to prevent low blood sugar; longer-acting basal insulin is less likely to cause low blood sugar. Avoid injecting insulin into the limbs that will be used for exercise.

During training

• During exercise, hormones that raise blood sugar are secreted, including adrenaline and glucagon, causing a temporary rise in blood sugar.
• Older patients with type 2 diabetes may develop hypoglycemia unawareness and worsening cognitive function; patients with autonomic neuropathy and long-standing type 1 diabetes may also have hypoglycemia unawareness because of a weakened hormonal response, so blood sugar management during exercise is recommended.
• Low blood sugar is defined as under 70 mg/dL and is a contraindication at the start of exercise; low blood sugar can also occur during exercise, with symptoms including trembling, weakness, unusual sweating, anxiety, tingling fingers, headache, slowed responses, seizures, and coma.
• Patients with retinopathy should avoid high-intensity exercise and situations with large rises in blood pressure.
• Be careful of dehydration and impaired heat regulation.
• During training, doing resistance exercise before aerobic exercise can reduce the risk of low blood sugar in people with type 1 diabetes.
• High blood sugar in people with type 1 diabetes can be life-threatening, with symptoms including frequent urination, fatigue, weakness, thirst, nausea and vomiting, rapid breathing, and fruity-smelling breath.
• People with diabetic foot problems or unhealed wounds should avoid water-based exercise and activities that could cause infection.
• Special patients are recommended for referral to physician-supervised training: those with autonomic neuropathy, kidney disease, peripheral arterial disease, and so on.

After training

• After 30 minutes or more of moderate-intensity or higher exercise, watch for post-exercise low blood sugar and take in carbohydrates as appropriate.
• Exercise-induced counterregulatory hormones can cause high blood sugar during or after exercise, in which case the timing and intensity of exercise should be adjusted.
• Based on the blood sugar changes during training, consider the possibility of a follow-up assessment to adjust medication doses.

Summary

An exercise prescription should take into account the frequency, intensity, type, and duration of past exercise, along with the patient’s age and social, economic, cultural, and physical condition, and be worked out together with a physician into an exercise plan suited to the individual.

An exercise prescription for people with diabetes is far from simple, because there are many details to consider. The initial step is to understand the past medical history, complications, dietary habits, and medication doses, then adjust based on cardiopulmonary function, muscle strength, joint range of motion, and exercise habits and experience. Over the past few years, diabetes treatment guidelines have paid more and more attention to exercise, which should make care for these patients more complete.

Further reading

Exercise Prescription for Hypertension

Exercise Prescription for Dyslipidemia

References

• ACSM guidelines for exercise testing and prescription
• NSCA’s essentials of training special populations
• 2018 Diabetes Clinical Care Guidelines (including the 2020 guideline UPDATE version)

Further reading

• Rehabilitation Exercise
• Sports Injury Overview
• PRP Prolotherapy
• Rehabilitation Exercise Prescription
• Pain Management