Exercise of Type 1 Diabetes and Type 2 Diabetes Disease: 

Firstly, the adjustments the athlete with diabetes might make if he or she wishes to exercise and, secondly, what the risks and benefits are, both in the short term and long term, of exercise to the patient with diabetes.

There are many examples of athletes with diabetes who have been extremely successful. British rower Steven Redgrave developed diabetes at the age of 35 having won gold medals at each of the previous four Olympic Games. Following his diagnosis he was able to continue training and competing and won a fifth consecutive gold medal in the Sydney Olympics Games 2000.

There are two distinct types of diabetes mellitus:

1. Insulin-Dependent (Type 1)
2. Non-Insulin-Dependent (Type 2)

Type 1 Diabetes

Type 1 Diabetes(Insulin-Dependent Diabetes Mellitus, IDDM), previously known as juvenile-onset diabetes, is thought to be an inherited autoimmune disease in which antibodies are produced against the beta cells of the pancreas. This ultimately results in the absence of endogenous insulin production, which is the characteristic feature of type 1 diabetes. The incidence of type 1 diabetes varies throughout the world but represents approximately 10-15% of diabetic cases in the western world. The onset commonly occurs in childhood and adolescence but can become symptomatic at any age. Insulin administration is essential to prevent ketosis, coma and death. The aims of treatment are tight control of blood glucose levels and prevention of micro vascular and macro vascular complications.

Type 2 Diabetes

Type 2 Diabetes (Non-Insulin-Dependent Diabetes Mellitus, NIDDM), previously know maturity-onset or adult-onset diabetes, is a disease as the former names suggest, of later onset ,linked to both genetic and lifestyle factors. It is characterized by diminished insulin secretion relative to serum glucose levels in conjunction with peripheral insulin resistance, both of which result in chronic hyperglycemia. Approximately 90% of individuals with diabetes have type 2 diabetes and it is thought to affect 3-7% of people in Western countries. The prevalence of type 2 diabetes increases with age. The pathogenesis of type 2 diabetes remains unknown but it is believed to be a heterogeneous disorder with a strong genetic factor. Approximately 80% of individuals with 2 diabetes are obese.

Type 2 diabetes is characterized by three major metabolic abnormalities:

• Impairment in pancreatic beta cells insulin secretion in response to a glucose stimulus.
• Reduced sensitivity to the action of insulin in major organ systems such as muscle, liver and adipose tissue.
• Excessive hepatic glucose production in the basal state.

Exercise and Diabetes:

The sports physician should be encouraged to work closely with the endocrinologist when considering exercise prescription for a diabetic patient. The target of an adult should be to achieve at least 30 minutes of continuous moderate activity, equivalent to brisk walking five or six days a week, with the flexibility of shorter bouts of more intense activity being considered important. This is provided that cardiovascular and hypertensive problems are taken into account. Heart rate may be an unreliable indicator of exertion because of autonomic neuropathy, and the rating of perceived exertion scales may be more useful.

Although exercise in conjunction with a proper diet and medications is the cornerstone in the treatment of diabetes, special care must be taken in those taking insulin. Both insulin and exercise independently facilitate glucose transport across the mitochondrial membrane by promoting GLUT4 transporter proteins from intracellular vesicles. The action of insulin and exercise is also cumulative. As such, an exercising type 1 diabetic will have lowered insulin requirements, and may notice up to a 30% reduction in insulin requirements with exercise. Importantly, in the person with type 1 diabetes, glycemic control may not be improved with regular exercise if changes in the individuals diet and insulin dosage do not appropriately match exercise requirements. In the absence of exercise, even for a few days, the increased insulin sensitivity begins to decline.

All patients with diabetes should carry an identification card or bracelet identifying them as having diabetes. They should be educated to be alert to the early signs of hypoglycemia for at least 6-12 hours after exercise. It is essential that they carry glucose tablets or an alternative source of glucose with them at all times. Dehydration during exercise should be prevented by adequate fluid consumption. It is also recommended that the diabetic athlete exercise with somebody else, if possible, in case of adverse reactions.

Benefits of Exercise:

• The benefits of exercise in type 1 diabetics include improved insulin sensitivity, improved blood lipid profiles, decreased heart rate and blood pressure at rest, decreased body weight and possible decreased risk of coronary heart disease.
• It does not appear that exercise improves glycemic control; however, insulin requirements may be decreased slightly.
• While exercise may not improve glucose control, the benefits of exercise in those with diabetes occur mainly through reducing the risk factors for cardiovascular disease.
• People with type 1 diabetes typically live longer if they participate in regular physical activity as a part of their lifestyle.
• It is well recognized that exercise reduces the risk of developing type 2 diabetes. There are also considerable benefits for those with type 2 diabetes.
• A program of regular physical activity can reverse many of the defects in metabolism of both fat and glucose that occur in people with type 2 diabetes.

As noted above, Hb is used as an index of long term blood glucose control. The lower the value, the better.  Hb is reduced by chronic exercise in people with type 2 diabetes. The evidence for improvement of Hb with exercise in type I diabetes is not as convincing.

Exercise and Type 1 Diabetes

Control of blood glucose is achieved in a patient with type 1 diabetes through a balance in the carbohydrate intake, exercise level and insulin dosage. The meal plan and insulin dosage should be adjusted according to the patient’s response to exercise. Unfortunately a degree of trial and error is necessary for type 1 diabetics taking up new activities. Frequent self-monitoring should occur, at least until a balance is achieved among diet, exercise and insulin parameters. Those with blood glucose levels less than 5.5 mmol/L (100 mg/dL) require a pre-exercise carbohydrate snack (e.g. sports drink, juice, glucose tablet, fruit).

• Exercise of 20-30 minutes at less than 70% VO (e.g. walking, golf, table tennis) requires a rapidly absorbable carbohydrate (15 g fruit exchange or 60 calories) before exercise but needs minimal insulin dosing adjustments.
• More vigorous activity of less than I hour (e.g. jogging, swimming, cycling, skiing, tennis) often requires a 25% reduction in pre-exercise insulin and 15-30 g of rapidly absorbed carbohydrate exchange before and every 30 minutes after the onset of activity.
• If early morning activity is to be performed the basal insulin from the evening dose of intermediate-acting insulin may need to be reduced by 20-50%, with checking of the morning blood glucose level.
• The morning regular-acting insulin dose may also need to be reduced by 30-50% before breakfast, or even omitted if exercise is performed before food.
• Depending on the intensity and duration of the initial activity and likelihood of further activity, a reduction of 30-50% may be needed with each subsequent meal.
• After exercise hyperglycemia will occur, but insulin should still be decreased by 25-50% (because insulin sensitivity is increased for 12-15 hours after activity has ceased).
• Consuming carbohydrates within 30 minutes after exhaustive, glycogen-depleting exercise allows for more efficient restoration of muscle glycogen.
• This will also help prevent post-exercise, late-onset hypoglycemia, which can occur up to 24 hours following such exercise.
• If exercise is unexpected, then insulin adjustment may be impossible. Instead, supplementation with 20-30 g of carbohydrate, at the onset of exercise and every 30 minutes thereafter, may prevent hypoglycemia.
• In elite athletes and with intense bouts of exercise, reductions in insulin dosage may be even higher than those listed above.
• During periods of inactivity (e.g. holidays, recovery from injury), increased insulin requirements are to be expected.

Exercise and Type 2 Diabetes

• Those patients with type 2 diabetes who are managed with diet therapy alone do not usually need to make any adjustments for exercise.
• Patients taking oral hypoglycemic drugs may need to halve their doses on days of prolonged exercise or withhold them altogether, depending on their blood glucose levels.
• They are also advised to carry some glucose with them and to be able to recognize the symptoms of hypoglycemia.
• Hypoglycemia is a particular risk in those people with diabetes taking sulfonylureas due to their long half lives and increased endogenous insulin production.
• Biguanides provide less of a problem as they do not increase insulin production.

Exercise and the Complications of Diabetes:

Exercise is often neglected when the secondary complications of diabetes occur. Some unique concerns for the patient with diabetes that warrant close scrutiny include autonomic and peripheral neuropathy, retinopathy and nephropathy. Poor glucose control appears to be associated with an increased occurrence of neuropathy.

• Abnormal autonomic function is common among those with diabetes of long duration.
• The risks of exercise when autonomic neuropathy is present include hypoglycemia, abnormal heart rate and blood pressure responses (e.g. postural drop), impaired sympathetic and parasympathetic nervous system activity and abnormal thermoregulation.
• Patients with autonomic neuropathy are at high risk of developing complications during exercise. Sudden death and myocardial infarction have been attributed to autonomic neuropathy and diabetes. High-intensity activity should be avoided, as should rapid changes in body position and extremes in temperature. Water activities and stationary cycling are recommended.
• Peripheral neuropathy (typically manifested as loss of sensation and of two point discrimination) usually begins symmetrically in the lower and upper extremities and progresses proximally.
• Podiatric review should occur on a regular basis, and correct footwear can prevent the onset of foot ulcers.
• Regular close inspection of the feet and use of proper footwear are important and the patient should avoid exercise that may cause trauma to the feet.
• Feet and toes should be kept dry and clean and dry socks should also be used.
• Non-weight-bearing activities, such as swimming, cycling and arm exercises, are recommended in those with insensitive feet.
• Activities that improve balance are appropriate choices.
• Diabetics with proliferative retinopathy should avoid exercise that increases systolic blood pressures to 170 mmHg and prolonged Valsalva-like activities.
• Exercise that increases blood pressure may worsen retinopathy.
• Exercise that results in a large increase in systolic pressure (such as weightlifting) can cause retinal hemorrhage.
• Exercise for these patients could include stationary cycling, walking and swimming. If possible, blood pressure should be monitored during the exercise program.
• Exercise is contraindicated if the individual has had recent photocoagulation treatment or surgery.
• These include lifting heavy weights and high-intensity aerobic activities. Activities that are weight-bearing yet low impact are preferable.
• It is important to wear well-cushioned shoes. Renal patients should be fully evaluated before commencing an exercise program. Fluid replacement is extremely important in these patients. Specific training programs for patients undergoing hemodialysis are advised.