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Exercise and Diabetes Mellitus

Optimizing Performance in Patients Who Have Type 1 Diabetes

Richard B. Birrer, MD, MPH; Vahid-David Sedaghat, MD

THE PHYSICIAN AND SPORTSMEDICINE - VOL 31 - NO. 5 - MAY 2003


In Brief: Those who have type 1 diabetes mellitus should include regular sports or recreational activities in their overall healthcare programs. Essential responsibilities of physicians who treat these patients include preparticipation clearance, education about blood glucose self-monitoring, exercise prescription, aggressive dietary and insulin management plans, identification of risk factors and potential complications, and ongoing education. Exercise has risks and benefits that must be understood so that participation yields a safe, enjoyable outcome that meshes with the patient's culture, activity goals, and lifestyle.

Diabetes mellitus is not a single disease but a heterogeneous group of disorders of absolute or relative insulin deficiency that afflicts 150 million people worldwide, including 16 million Americans. By 2025, the number with diabetes is projected to surpass 300 million, making the disease pandemic.1 Currently, its classification is arbitrary and consists of two major categories and other less frequent types. This article will concentrate on type 1 diabetes mellitus, which constitutes 10% of the disease.

Type 1 diabetes is characterized by autoimmune-mediated destruction of pancreatic beta-cells, leading to insulinopenia. About half of type 1 patients are younger than 20, with a prevalence in this age-group of about 2.5 to 3.5 per 1,000.2 Evidence supports a genetic predisposition among Caucasian populations. Strong associations exist between specific histocompatibility antigen (HLA) alleles on chromosome six (HLA DR3/DR4) in more than 90% of affected individuals. A defined factor, endogenous or exogenous, capable of inducing type 1 diabetes is still being investigated, and possible candidates under intense scrutiny include numerous viruses, food products, toxins, and environmental triggers.2 Patients with type 1 diabetes require exogenous insulin for survival and are at risk of developing serious complications, including ketoacidosis, during periods of stress or missed insulin administration.

The General Effects of Exercise

Exercise is as desirable for patients with diabetes mellitus as it is for unaffected people.2,3 In patients who have type 1 diabetes, exercise training coupled with improved glycemic control decreases muscle capillary basement membrane thickening and arterial pulse volume recordings and increases lean body mass and work capacity.4 Exercise improves glucose tolerance by augmenting insulin sensitivity through enhanced receptor affinity and a decreased insulin requirement for adequate glycemic control.5 Furthermore, exercise reduces abdominal fat, improves weight management, and combats obesity. Other potential benefits of exercise include reducing serum total cholesterol, triglyceride, low-density lipoprotein (LDL), and very low-density lipoprotein (VLDL) levels, with a concomitant increase in high-density lipoprotein (HDL) concentration, all of which inhibit the early development and progression of atherosclerotic plaques and subsequent vascular compromise.6,7

Physical training allows a patient with diabetes mellitus to "comprehend one's own body," particularly when determining blood glucose levels, managing insulin dosing, and adjusting diet to avoid hypoglycemia. The added training allows patients to feel more in control of their condition. Those who participate in an exercise regimen feel an improvement in their quality of life, leading to an enhancement in self-esteem and sense of well-being.8

Exercise training should always be considered an adjunct, however, and never a substitute for intensified insulin and dietary therapy, long-term metabolic control, and prevention of microvascular complications.9 Although exercise has not shown any demonstrable adverse effects in patients with uncomplicated disease, recent studies3,9 have failed to show a beneficial effect of exercise on long-term metabolic control in patients with type 1 diabetes. However, significant adaptation in cardiac function has been observed in type 1 patients: Those who perform three 20-minute sessions of moderate exercise per week decrease their morbidity and mortality.2

Glucose Physiology and Pathophysiology

Plasma glucose levels in exercising patients who do not have diabetes remain relatively stable because of the intricate autonomic and hormonal regulation. The exercising muscle increases glucose uptake and oxygen consumption 20-fold, initiates glycogenolysis and lipolysis, and stimulates hepatic glucose output.10-13 Replenishing glycogen stores may take up to 24 to 48 hours, and postexercise recovery, particularly after exhaustive work, is characterized by enhanced insulin sensitivity. Trained athletes use glucose more efficiently than do sedentary individuals who exercise at a comparable intensity and duration. The patient with diabetes who exercises may have a decreased insulin requirement that allows the body to modulate the precise endocrine control needed to increase fuel mobilization and subsequent substrate oxidation within the working muscle. Acute effects of exercise generally reduce plasma glucose levels. Chronic exercise will result in improved insulin sensitivity and glucose utilization that, together with a leaner body composition and enhanced psychological well-being, usually impart a positive effect on any patient.

The physiologic response to exercise depends on the type of diabetes, degree of control, bioavailability of insulin, diet, and fitness level achieved with exercise. Patients with type 1 diabetes who have lost the normal compensatory decrease in insulin secretion that accompanies exercise are faced with unique challenges before, during, and after exercise to avoid metabolic decompensation.2 This is particularly true for children with the disorder. They have a greater variability in blood glucose levels than adults. Additionally, peripubertal hormonal changes make glycemic control a challenge during adolescence.

Hypoglycemia during and several hours after exercise becomes an increasing risk factor. This risk arises from the lack of neural inhibition for the release of insulin at the subcutaneous injection site, leading to excessive levels (overinsulinization), which suppresses glycogenolysis and gluconeogenesis and allows peripheral availability of insulin to far exceed glucose production. The risk of hyperglycemia, lipolysis, ketogenesis, and, ultimately, ketoacidosis during exercise is most evident in patients with poorly regulated type 1 diabetes in whom a relative insulin deficiency (underinsulinization) exists. Exercise, superimposed on a relative insulin deficiency, increases blood glucose levels through one of several mechanisms: increasing hepatic gluconeogenesis and glycogenolysis, stimulating counterregulatory hormone dysfunction (delayed release of glucagon, growth hormone, and cortisol), and desensitizing reactions to catecholamines. Therefore, adequate insulin availability and good metabolic control are important to control the hormonal response of exercise in all patients who have type 1 diabetes.

Diagnosing Type 1 Diabetes

Diagnosis is based on three criteria, all of which must be met. The first is a fasting blood glucose level (no calorie intake for 8 hours) equal to or exceeding 126 mg/dL. The second is a 2-hour blood glucose level equal to or exceeding 200 mg/dL after an oral challenge of 75 g of glucose in liquid. The third is a random blood glucose concentration equal to or exceeding 200 mg/mL in association with weight loss, polyuria, and polydipsia.

Preexercise Clinical Evaluation

It is important for the partnering physician to perform a thorough evaluation before patients start an exercise regimen.3,14 Physicians should pay careful attention to the cardiovascular (blood pressure, signs of micro- and macrovascular disease), neurologic (neuropathy), musculoskeletal (joints, feet), ophthalmologic (retinopathy), renal (nephropathy), and gastrointestinal (paresis, diarrhea) systems. Important psychosocial issues include athlete motivation and maturity. The identification and documentation of the loss of one of any paired organ is critical. A graded stress test is appropriate if the patient has significant risk factors (age >35 years, has had type 1 diabetes for >15 years, has macro- or microvascular disease). Doppler studies are reserved for patients with clinical evidence of peripheral arterial disease. A complete ophthalmologic exam, including direct retinoscopy, should be performed yearly.

Of particular importance is the patient's degree of normal day-to-day glycemic control (self-care skills and knowledge base [self-monitoring of blood glucose, injection technique, pump use, carbohydrate counting, sick-day protocol]), fundamental knowledge for anticipating hypoglycemia, and early recognition of the onset of potential long-term complications associated with long-standing disease, such as noticing changes in vision and reporting them to the physician.9

Children and adolescents with the disorder will manifest microvascular complications of hyperglycemia well before 10 years' duration, especially if control has been poor. Although early changes are subtle and difficult to recognize, they often will be exacerbated by puberty. The increase in growth, sexual development, and associated insulin requirements, as well as a tendency for some individuals to become less motivated and compliant with their regimens, tend to accelerate the rate of progression and severity of complications. Lastly, the choice of physical activity and optimal performance level requires consideration of the activity type, training and competition schedule, appropriateness of support staff, and availability of resources. Matching activity time with insulin peaks and blood glucose levels is essential. High-risk activities include scuba and sky diving, rock and mountain climbing, and solo endurance activities (hiking, running, swimming, cycling, etc).

Elements of the Activity Prescription

Several factors come into play when considering athletic activities.

Diet and insulin dose. A rapidly absorbed carbohydrate in the form of simple sugar (eg, fruit juice, hard candy) must be available during the activity, whereas a slowly digested form (eg, raw corn starch, a whole wheat bagel, a slice of whole grain bread) is appropriate if there is a risk of nocturnal hypoglycemia. Any estimate of the amount of carbohydrate required to maintain euglycemia during exercise is only an approximation. The actual amount will depend on frequent self-monitoring, with the interval determined by the type and intensity of the exercise. Early in the season, more frequent self-monitoring of blood glucose levels is necessary until a balance is achieved among diet, exercise, and insulin parameters. Testing 30 minutes before activity and again just before starting the activity will help determine if the blood glucose level is stable or dropping too fast. If levels are falling too rapidly, a snack before exercise can be added. This practice may be most helpful when planning to exercise near or at the time that the long-acting insulin peak is expected. Early on, patients should be strongly encouraged to test their blood glucose levels every 30 to 45 minutes, from initiation until completion of a sports activity. This protocol enables patients to ascertain exercise effects on glycemic control and also to intervene by halting their activity for urgent glycemic support.

Once patients have obtained routine stable equilibrium with exercise regimens, requirements, and performance, as well as mastered the intricacies of glycemic response to particular training programs, they will be able to modulate the need for finger-stick monitoring and rest. Such a routine will produce less disruption of sports and contribute to fulfillment and more normal workouts.

The ideal preexercise blood glucose level is 120 to 180 mg/dL. Patients who have blood glucose concentrations exceeding 200 mg/dL and ketones in their urine, or blood glucose concentrations more than 300 mg/dL regardless of ketone status, should postpone exercise and take supplemental insulin. Patients who have blood glucose levels less than 100 mg/dL will always require a preexercise carbohydrate snack, regardless of the type of activity planned.

Exercise intensity and duration. These general guidelines provide useful starting points for individual patients to discover how exercise affects their glycemic control (table 1),15 but regimens must be individualized.

TABLE 1. Training and Nutritional Requirements for Patients With Type 1 Diabetes Mellitus

Phase of Training Recreational Athlete Endurance Athlete

Daily training Consume <30% of total daily energy from fat,
10%-12% from protein, and the rest from CHO
Consume <0.4 g fat, 0.8-1.2 g protein,
and 8-10 g CHO per kg BW per day
CHO loading
(week before the event)
Not applicable Caution: Do 90, 40, 40, 20, 20, 0 minutes of
moderate intensity exercise per day,
consuming 5 g CHO per kg BW per day
during first 3 days, then 8-10 g CHO per kg
BW per day in the next 3 days
Hours before the event Exercise does not have to be done on an empty
stomach; CHO meal has little effect on
exercise; consume adequate fluids
Consume 4-5 g CHO per kg BW 3-4 hr before
event and consume 1-2 g liquid CHO per kg BW
1 hr before the event. Solids may be substituted
During event Consume 250 mL fluid every 20 min
or at a rate equal to sweat loss; fluids
may be CHO- or electrolyte-containing water
Consume 250 mL fluid every 20 min or at a rate
equal to sweat loss; preferred fluids are CHO
or electrolyte (6%-10% weight/volume)
drinks taken at a rate to provide 40-65 g
CHO per hr. If CHO intake is delayed, take
200 g of liquid CHO before completing 2 hr of
exercise and then consume 40-65 g CHO per hr
4-6 hr after the event Not applicable Consume 0.7-3.0 g CHO per kg BW
immediately after event and every 2 hr for 4 hr;
if tolerated, postevent regimen can be 0.4 g
CHO per kg BW every 15 min for 4 hr
24 hr after the event Follow daily training schedule Consume 8-10 g CHO per kg BW per day; mixed
CHO foods can be taken; high-glycemic-index
foods promote glycogen synthesis

Reproduced with permission from Ruderman N, Devlin JT (eds): The Health Professional's Guide to Diabetes

CHO = carbohydrate; BW = body weight

Short-term exercise that is not exhaustive, such as walking, golf, badminton, table tennis, calisthenics, or dancing, requires a rapidly absorbable carbohydrate (15 g fruit exchange or 60 calories) before exercise. In this instance, insulin reduction is not recommended.

More vigorous competitive activity that is less than 1 hour long, such as soccer, basketball, racquetball, tennis, timed calisthenics, jogging, swimming, leisure skiing, or cycling, often require a 25% reduction in preexercise insulin and 15 to 30 g of rapidly absorbed carbohydrate exchange before and every 30 minutes after the onset of activity.

Strenuous activity that lasts for longer than 1 hour or endurance exercises, such as marathon running, backpacking, triathlon, hiking, or cross-country or downhill skiing, will often require a 30% to 80% reduction in insulin dose and ingestion of 2 fruit exchanges (30 g or 100 to 120 calories) every 30 minutes. Excess insulin exacerbates the hypoglycemic effect more during intense rather than moderate exercise. It is imperative that physicians warn patients that sustained activity requires frequent self-monitoring of blood glucose levels.

Unanticipated exercise requires additional intake. For patients who engage in mild exercise, give 1 fruit exchange every 30 minutes; for moderate exercise, give 1 starch exchange (15 g carbohydrate or 80 calories) and 1 protein exchange (50 calories) before exercise followed by 1 fruit exchange every 30 minutes. For those doing strenuous exercise, such as a pickup basketball game or unscheduled training, give 2 starch exchanges and 1 protein exchange before exercise, followed by 2 fruit exchanges every 30 minutes of exercise.

Energy requirements and insulin. Individuals exercising at 50% of the athlete's maximum oxygen consumption (50% VO2max) derive approximately 50% of their energy (5 kcal/min, 1.25 g of glucose per minute) from glucose oxidation.16 Usually, the intensity of the exercise at 50% VO2max is comparable to exercise being performed at 60% to 85% of estimated maximal heart rate (in adults, this value corresponds to 220 minus age in years). Thus, we can estimate approximately 1 g of carbohydrate per minute of moderate exercise. Tamis-Jortberg et al17 noted that appropriate intake requires 17 g of carbohydrate at the initiation of activity and 17 g every 15 minutes for 60 minutes of exercise at 65% VO2max, followed by 15 g (15 to 30 g for intense exercise) for each subsequent hour.

Endurance exercise also increases insulin sensitivity after activity, so the insulin dose taken the next day should be reduced. The percent of insulin reduction or the quantity of carbohydrate supplementation will always depend on the person's fitness level, sensitivity to insulin, and the duration, intensity, and caloric requirements for the particular exercise program.18

Insulin dosage regimens (table 2) may be standard (two injections of mixed short and intermediate insulins), intensive (three or more injections/day), extended (glargine or insulin zinc suspension for basal needs plus lispro for meals with either), or continuous infusion by pump. The standard regimen is the easiest to perform, but it is difficult to match with exercise and does not give good metabolic control. The intensive protocol provides better control, offers flexibility, and reduces the risk of hypoglycemia but is harder to learn and requires more frequent testing. The extended regimen, while difficult to master, is very flexible and provides excellent metabolic control and the lowest risk of hypoglycemia.

TABLE 2. Insulin Types and Their Characteristics

Type Formulation* Peak (hr) Duration (hr) Comments

Short-acting Zinc suspension
(Semilente)
Insulin aspart
(NovoLog)
Insulin lispro
protamine (Humalog)
5-10

1-3

0.5-1.5
12-16

3-5

6-8
Meal coverage if taken before eating;
insulin of choice for pumps; mixes
with NPH and Ultralente
Regular Regular
(Humulin R, Novolin R,
Velosulin BR
Iletin II R [pork])
2 8-12 Meal coverage if taken 30-45 min before
eating; long activity may lead to
hypoglycemia; compatible with all
other insulins
Intermediate Insulin zinc
suspension
(Humulin L, Novolin L,
Lente)

Isophane insulin
suspension
(Humulin N, Novolin L,
Lente) and Insulin NPH
(Novolin N, Humulin N,
Iletin II NPH [pork])
7-15




4-12
24




24
Basal, between meals; requires snacks
to cover extended time between
meals; peaks before or after lunch;
mixes with regular and Semilente

Lunch coverage if taken in the morning; can
cause hypoglycemia because of early activity
or lingering effect; mixes with regular insulin
Long-acting Insulin glargine
(Lantus)

Protamine zinc insulin

Insulin zinc
(various human and pork)
5


14-24

10-30
24


36

>36
Basal; one daily dose; cannot be mixed
with other insulins

Mixes with regular insulin

Basal, between meals; can be used once a
day, but dose is often split; mixes with
regular and Semilente

*Generic names are given first with some available brand names in parentheses.

NPH = neutral proamine hagedorn

Insulin dosage adjustments. These are made as follows: If the anticipated exercise will exceed 1 hour in the morning, make a 25% reduction in before-breakfast regular insulin for moderate activity, and 35% to 50% reduction for vigorous or sustained activity. For afternoon exercise, patients reduce the longer-acting insulin (NPH or Lente) before-breakfast dose as for morning activity. For evening exercise, patients reduce both regular and longer-acting insulins before the supper dose as noted. Athletes do better on at least two injections a day. The preferred preexercise injection should be done in a neutral site such as the abdomen. This prevents hypoglycemia from enhanced absorption caused by injection into an exercising limb.

For patients who use continuous subcutaneous insulin infusion pumps, metabolic control is excellent, and the risk for delayed hypoglycemia is significantly decreased as long as the insulin infusion rate is decreased in advance. The pump is about the size of a pager and can be worn on the wrist, belt, or in a pack (see "Pumping Insulin During Exercise: What Healthcare Providers and Diabetic Patients Need to Know"). A reduced temporary basal infusion rate can be set before the activity to avoid inducing hypoglycemia yet still maintaining the infusion potency. In addition, reduced basal rates can be programmed to avoid postexercise hypoglycemia.

Newer insulin pumps offer waterproof and disconnect features that make them highly versatile and preferred by many athletes. Although the devices are expensive ($6,000 to $7,000, excluding the cost of the infusion sets) and somewhat difficult to learn how to use properly, more than 80,000 patients with type 1 diabetes use them.

For activities that have extreme movement and contact (eg, martial arts, gymnastics) in the region where the infusion set is attached, patients may detach the pump and inject subcutaneous insulin for glucose control. No replacement is needed if the pump is removed for less than an hour. The manual dose equals what the pump would have delivered during the time the set is removed.

Activity components and special precautions. Proper warm-up and cooldown periods are essential. Low-intensity aerobic activities (eg, cycling, swimming, walking) for 5 to 10 minutes are appropriate for the warm-up. A 5- to 10-minute period of general and activity-specific flexibility exercises should follow the warm-up. During the cooldown period (5 to 10 minutes), the heart rate gradually returns to preexercise levels.

The feet require special attention in exercise. Patients should wear athletic shoes with cushioned midsoles (silica gel or air cells) that are "broken in" and polyester or blend (cotton-polyester) socks that reduce shear forces and moisture buildup. These steps minimize trauma and blisters. Patients should be taught to examine their feet before and after exercise.

Adequate hydration is crucial for athletes with diabetes, and appropriate measures should be taken to prevent dehydration by planning a liberal fluid intake before, during, and after prolonged exercise. Care must be taken to ensure isoosmolality (normal salinity) of the replacement fluid as well as to avoid any inadvertent caloric contents. Proper hydration before, during, and after physical activity significantly helps glycemic control and cardiopulmonary function.

While neuropathy is rare in most type 1 patients younger than 20, heat and cold intolerance from autonomic dysfunction and syncopal episodes because of relative bradycardia can occur. Exercise in extremely hot or cold environments, therefore, should be approached with caution and adequate preparation. A diabetic identification bracelet or footwear tag should be worn visibly at all times.

Heavy weight lifting, strenuous isotonic exercises, or collision sports should be avoided by all type 1 patients except those with new-onset disease, since inherent Valsalva's maneuvers can lead to cardiovascular and ophthalmologic complications. Alternatives such as moderate weight training with high repetitions are recommended.

The choice of activity should reflect the interests, goals, and lifestyle of the athlete. During childhood, the need for glycemic control must be balanced with normal play and, during adolescence, with peer relationships.

Risks and Complications

The three major problems of exercise in patients with type 1 diabetes are hypoglycemia, hyperglycemia with ketosis, and chronic degenerative complications.

Variations in physical activity (exercise routine) and injection sites may alter daily insulin requirements in individuals attempting to maintain near normal blood glucose levels. The balance between insulin action and counterregulatory hormones may not occur during aerobic exercise in athlete with diabetes, leading to hypo- or hyperglycemia. The expected decline of insulin with activity may not be seen because of the use of exogenous insulin.

Hypoglycemia. The prevention of hypoglycemia requires planning, a thorough knowledge of the appropriate timing of injections, and awareness of the duration of action of the insulin used. The injection of insulin into an exercising limb may result in hypoglycemia because of enhanced absorption.19 The timing of the athletic events in relation to insulin administration is also critical. Optimal athletic performance in athletes with diabetes requires a blood glucose level between 70 and 150 mg/dL. Finally, the dietary strategies and caloric augmentation used to avoid interactivity hypoglycemia also play a critical role in a successful exercise regimen.

The manifestations of hypoglycemia are varied and may differ significantly between children and adults who use insulin. In adults, at least 11 key hypoglycemic symptoms can be manifested, and each can be divided into three subgroups: autonomic, neuroglycopenic, and nonspecific (malaise, nausea, or headache).

In general, manifestations begin with early autonomic symptoms such as sweating, tremors, palpitations, pallor, hunger, and mydriasis. These symptoms may be related to the rapid rate of blood glucose decline rather than the actual level. Symptoms usually resolve if patients ingest a rapid-acting carbohydrate, which should always be readily available, and cease the activity. Carbohydrate gels that can be applied to the gums and then swallowed should be used only in alert, cooperative athletes.

Neuroglycopenic symptoms. These may be related to failure of brain cells to receive sufficient glucose to function. Neuroglycopenic symptoms are characterized by confusion, drowsiness, inappropriate behavior, speech difficulty, incoordination, and loss of judgment. Unless hypoglycemia is corrected, it may lead to lethargy, coma, convulsions, permanent brain injury, and possibly death. It is well known that many children manifest changes in behavior or a combination of all these symptoms, and it is important for the patient, parents, and sports team to recognize them quickly.

It is paramount for the physician to differentiate the normal "fight or flight" sympathetic response of before-competition and competition-associated anxiety, since this response will also mimic the adrenergic autonomic symptoms of hypoglycemia. These two opposing entities can be differentiated only by performing spot blood glucose monitoring. If the blood glucose concentration is less than 100 mg/dL or the athlete has taken short-acting insulin less than 90 minutes before exercise, supplemental preexercise carbohydrate should be taken. Furthermore, patients should follow the general rule that subtracting 1 U of regular insulin from the usual dose or adding 15 g of carbohydrate increases blood glucose levels by approximately 50 mg/dL.20 If testing is not available, it is always prudent to treat any symptom as hypoglycemia until it is proven otherwise (table 3).

TABLE 3. How to Manage a Hypoglycemic Reaction During Activity
  1. Stop the activity immediately.
  2. Have the patient take a rapid-acting carbohydrate (3-4 glucose tablets [4 g each] or a half cup of apple or orange juice).
  3. Have the patient eat one starch exchange before resuming activity (eg, 2 tsp peanut butter or 1 oz cheese and crackers).
  4. Rest 15 min to allow carbohydrate absorption.
  5. Patient can resume activity when he or she feels better and blood glucose levels are >100 mg/dL.
  6. If hypoglycemia is severe, administer intramuscular glucagon (0.1 mg/kg to a maximum 1 mg/kg if patient weighs <10 kg or is younger than 3; 1.0 mg/kg to a maximum of 10 mg/kg for patients weighing >10 kg or older than 3). If the patient does not respond, transport to medical facility for intravenous glucose infusion. If the patient responds, he or she will still require supplementary carbohydrate.

The heterogeneous responses to exercise in patients with type 1 diabetes make it impossible to give precise guidelines for diet and insulin adjustment. The risk of hypoglycemia appears to be lowest if one engages in exercise in the morning before the breakfast insulin dose. However, this option seems unrealistic for most young people. Maintaining consistency in when one exercises and type of exercise performed will make adaptations in insulin and diet therapy more feasible. One must also remember that compliance with any exercise program will improve if the activity selected is enjoyable.

Late-onset hypoglycemia and hyperglycemia. Postexercise, late-onset hypoglycemia, occurring up to 28 hours after the completion of vigorous exercise (average time of onset, 6 to 12 hours) has been reported in those treated with insulin as well as in those on oral hypoglycemics.14 This phenomenon has been attributed to increased glucose uptake and glycogen synthesis in previously exercised muscle groups and requires increased carbohydrate requirements for up to 24 hours after vigorous exercise. The replacement of glycogen stores within 1 hour of exercise (the "golden replenishment period") is the best preventive strategy. Other options include avoiding exercise before bedtime, reducing an insulin dose that peaks during the postexercise period, avoiding intermediate-acting insulin during the afternoon or early evening, or using long-acting insulin that does not peak.

Exercise-induced hyperglycemia and ketosis can be prevented by delaying acute exercise if the fasting blood glucose concentration exceeds 250 mg/dL and urinary ketones are present at rest or if the random blood glucose is greater than 300 mg/dL. Management includes administration of supplemental insulin to reestablish good metabolic control. Acute exercise may further aggravate hyperglycemia and ketogenesis. Occasionally, individuals with type 1 diabetes will have blood glucose levels greater than 250 mg/dL and no urinary ketones and opt to exercise to lower their blood glucose levels. Doing so warrants caution, and patients should continue monitoring for drastic changes in blood glucose levels or the appearance of ketones. Under such circumstances, estimates suggest that a 70-kg (154-lb) individual would need to consume 5 g less carbohydrate for each 50 mg/dL increment above the desired blood glucose level.21 Rarely will patients with well-controlled diabetes develop "rebound hyperglycemia"—an acute rise in blood glucose levels after high-intensity exercise. This phenomenon may stem from excessive sympathetic stimulation that causes counterregulatory hormone release and a resultant increase in glycogenolysis and hepatic glucose output. Exercising at a slow, steady pace, with a gradual increase in activity over time to achieve optimal endurance, will avoid this complication.

The Keys to Glycemic Control

Patients with well-controlled uncomplicated type 1 diabetes can perform almost any sports or recreational activity if they adopt an integrated team approach and have good social support (table 4). Many are outstanding amateur and professional athletes. Exercise is beneficial in treating patients who have diabetes for the same reasons that it is prescribed in nondiabetic patients. The sports physician's role is one of preparticipation clearance, advocacy, and education.

TABLE 4. Guidelines for Planning an Exercise Program for Those With Type 1 Diabetes

Physicians, coaches, and trainers can easily remember the guidelines with the mnemonic DIABETES:
DietEducate patients about proper diet and hydration before, during, and after exercise. Patients should have simple carbohydrates available during activities (see table 3). Several concentrated gel and liquid forms are available for rapid absorption. Knowing the approximate calories used in each sport can help determine insulin dosage and diet strategies.
InsulinEnsure that patients know the peak insulin actions and appropriate reductions in dosage for activity. Use a neutral insulin injection site (eg, abdomen). Glucagon should be available for cases of severe hypoglycemia with unconsciousness. The drug acts in 5-20 min, but a glucose infusion may also be needed. Once patients are awake and can take food, they should be given rapid-acting carbohydrates. In these cases, medical consultation is desirable.
AcidosisTell patients that they can effectively circumvent this complication if they postpone exercise when blood glucose levels exceed 250 mg/dL and urinary ketones are present, or when blood glucose levels exceed 300 mg/dL without urinary ketones.
Blood glucoseDiscuss values at which patients should take supplemental carbohydrate and supplemental insulin. If levels are less than 100 mg/dL, patients should take a pregame snack. Ideal preexercise blood glucose levels are 120-180 mg/dL.
ExerciseAdvise patients that all workouts should include warm-up and cooldown sessions. Stretching is done to enhance flexibility and prevent injury. Match patients to exercise regimen. Encourage patients to learn their individual blood glucose responses to different forms of exercise and foods.
TimingTeach patients about food composition so that they can portion appropriately and consume at the correct intervals to prevent hypoglycemia. Direct athletes to postpone exercise if insulin injection has been taken less than 60-90 minutes before activity.
EvaluationBefore initiating a vigorous exercise regimen, patients should have a thorough preparticipation examination to exclude degenerative complications that may limit certain activities.
Social acceptanceInform patients that they should have a prearranged signal with coaches and teammates to ensure rapid delivery of carbohydrates in an emergency. Athletes should educate their coaches, athletic trainers, and teammates about the symptoms of hypoglycemia and its treatment. Advocate exercising with another person and carrying a diabetes identification band or tag.

References

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  3. American College of Sports Medicine and American Diabetes Association joint position statement: Diabetes mellitus and exercise. Med Sci Sports Exerc 1997;29(12):i-vi
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  10. Galbo H: The hormonal response to exercise. Diabetes Metab Rev 1986;1(4):385-408
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  15. Ruderman N, Devlin JT (eds): The Health Professional's Guide to Diabetes and Exercise. Alexandria, VA, American Diabetes Association, 1995, p 94
  16. Houmard JA, Egan PC, Neufer PD, et al: Elevated skeletal muscle glucose transporter levels in exercise-trained middle-aged men. Am J Physiol 1991;261(4 pt 1):E437-E443
  17. Tamis-Jortberg B, Downs DA Jr, Colten ME: Effects of glucose polymer sports drink on blood glucose, insulin, and performance in subjects with diabetes. Diabetes Educ 1996;22(5):471-487
  18. AMA Council on Scientific Affairs: Advisory Council on Diabetic Athletes, American Medical Association, Chicago, 1980
  19. Frid A, Ostman J, Linde B: Hypoglycemia risk during exercise after intramuscular injection of insulin in the thigh in IDDM. Diabetes Care 1990;13(5):473-477
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  21. Zinker BA: Nutrition and exercise in individuals with diabetes. Clin Sports Med 1999;18(3):585-606

Dr Birrer is senior vice president and chief medical officer, and Dr Sedaghat is chief resident in the department of medicine and pediatrics at Saint Joseph's Regional Medical Center in Paterson, New Jersey. Address correspondence to Richard B. Birrer, MD, MPH, 703 Main St, Paterson, NJ 07503; e-mail to [email protected].

Disclosure information: Drs Birrer and Sedaghat disclose no significant relationship with any manufacturer of any commercial product mentioned in this article. No drug is mentioned in this article for an unlabeled use.


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