VOL. 17 NO. 4 1999
Diabetes Mellitus and Exercise
American Diabetes Association
Reprinted with permission from Diabetes Care 22
(Suppl 1):S49-53, 1999. The recommendations in this article are based on the evidence
reviewed in the following publications: Exercise and NIDDM (Technical Review). Diabetes
Care 13:785-89, 1990; and Exercise in individuals with IDDM (Technical Review). Diabetes
Care 17:924-37, 1994.
During exercise, whole-body
oxygen consumption may increase by as much as 20-fold, and even greater increases may
occur in the working muscles. To meet its energy needs under these circumstances, skeletal
muscle uses, at a greatly increased rate, its own stores of glycogen and triglycerides, as
well as free fatty acids (FFAs) derived from the breakdown of adipose tissue triglycerides
and glucose released from the liver. To preserve central nervous system function, blood
glucose levels are remarkably well maintained during exercise. Hypoglycemia during
exercise rarely occurs in nondiabetic individuals. The metabolic adjustments that preserve
normoglycemia during exercise are in large part hormonally mediated. A decrease in plasma
insulin and the presence of glucagon appear to be necessary for the early increase in
hepatic glucose production during exercise, and during prolonged exercise, increases in
plasma glucagon and catecholamines appear to play a key role. 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 counterinsulin hormones during exercise 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 exercise, and hypoglycemia may ensue. Similar concerns exist
in patients with type 2 diabetes on insulin or sulfonylurea therapy; however, in general,
hypoglycemia during exercise tends to be less of a problem in this population. Indeed, in
patients with type 2 diabetes, exercise may improve insulin sensitivity and assist in
diminishing elevated blood glucose levels into the normal range.
of this position statement is to update and crystallize current thinking on the role of
exercise in patients with types 1 and 2 diabetes. With the publication of new clinical
reviews, it is becoming increasingly clear that exercise may be a therapeutic tool in a
variety of patients with, or at risk for diabetes, but that like any therapy its effects
must be thoroughly understood.13 From a practical point of view, this means
that the diabetes health care team will be required to understand how to analyze the risks
and benefits of exercise in a given patient. Furthermore, the team, consisting of but not
limited to the physician, nurse, dietitian, mental health professional, and patient, will
benefit from working with an individual with knowledge and training in exercise
physiology. Finally, it has also become clear that it will be the role of this team to
educate primary care physicians and others involved in the care of a given patient.
EVALUATION OF THE
Before beginning an
exercise program, the individual with diabetes mellitus should undergo a detailed medical
evaluation with appropriate diagnostic studies. This examination should carefully screen
for the presence of macro- and microvascular complications that may be worsened by the
exercise program. Identification of areas of concern will allow the design of an
individualized exercise prescription that can minimize risk to the patient. Most of the
following recommendations are excerpts from The Health Professional's Guide to Diabetes
medical history and physical examination should focus on the symptoms and signs of disease
affecting the heart and blood vessels, eyes, kidneys, and nervous system.
A graded exercise
test may be helpful if a patient, about to embark on a moderate- to high-intensity
exercise program (Table 1)46, is at high risk for underlying cardiovascular
disease, based on one of the following criteria:
- age >35
- type 2 diabetes of
>10 years' duration
- type 1 diabetes of
>15 years' duration
- presence of any
additional risk factor for coronary artery disease
- presence of
microvascular disease (retinopathy or nephropathy, includng microalbuminuria)
patients who exhibit nonspecific electrocardiogram (ECG) changes in response to exercise,
or who have nonspecific ST and T wave changes on the resting ECG, alternative tests such
as radionuclide stress testing may be performed. In patients planning to participate in
low-intensity forms of exercise (<60% of maximal heart rate) such as walking, the
physician should use clinical judgment in deciding whether to recommend an exercise stress
test. Patients with known coronary artery disease should undergo a supervised evaluation
of the ischemic response to exercise, ischemic threshold, and the propensity to arrhythmia
during exercise. In many cases, left ventricular systolic function at rest and during its
response to exercise should be assessed.
peripheral arterial disease (PAD) is based on signs and symptoms, including intermittent
claudication, cold feet, decreased or absent pulses, atrophy of subcutaneous tissues, and
hair loss. The basic treatment for intermittent claudication is nonsmoking and a
supervised exercise program. The presence of a dorsalis pedis and posterior tibial pulse
does not rule out ischemic changes in the forefoot. If there is any question about blood
flow to the forefoot and toes on physical examination, toe pressures as well as Doppler
pressures at the ankle should be carried out.
The eye examination
schedule should follow the American Diabetes Association's Clinical Practice
Recommendations. For patients who have proliferative diabetic retinopathy (PDR) that
is active, strenuous activity may precipitate vitreous hemorrhage or traction retinal
detachment. These individuals should avoid anaerobic exercise and exercise that involves
straining, jarring, or Valsalva-like maneuvers.
|Table 2. Considerations for Activity Limitation in
|Level of DR
by medical status
by medical status
by medical status
by medical status
by medical status
that dramatically elevated blood pressure
by medical status
that substantially increase systolic blood presure, Valsalva maneuvers, and active jarring
Heavy competitive sorts
months (may require laser surgery)
activities, Valsalva maneuvers, pounding or jarring
Strenuous trumpet playing
months (may require laser surgery)
diabetic retinopathy; NPDR, nonproliferative diabetic retinopathy.
On the basis of the Joslin Clinic experience, the degree
of diabetic retinopathy has been used to stratify the risk of exercise, and to
individually tailor the exercise prescription. Table 2 is reproduced, with minor
modifications, from The Health Professional's Guide to Diabetes and Exercise.3
recommendations have not been developed for patients with incipient (microalbuminuria
>20 mg/min albumin excretion) or overt nephropathy (>200 mg/min). Patients with
overt nephropathy often have a reduced capacity for exercise, which leads to
self-limitation in activity level. Although there is no clear reason to limit low- to
moderate-intensity forms of activity, high-intensity or strenuous exercises should
probably be discouraged in these individuals.
|Table 3. Exercises
for Diabetic Patients With Loss of Protective Sensation
Other non-weight-bearing exercise
neuropathy (PN) may result in loss of protective sensation in the feet. Significant PN is
an indication to limit weight-bearing exercise. Repetitive exercise on insensitive feet
can ultimately lead to ulceration and fractures. Evaluation of PN can be made by checking
the deep tendon reflexes, vibratory sense, and position sense. Touch sensation can best be
evaluated by using monofilaments. The inability to detect sensation using the 5.07 (10 g)
monofilament is indicative of the loss of protective sensation. Table 3 lists
contraindicated and recommended exercises for patients with loss of protective sensation
in the feet.
The presence of
autonomic neuropathy may limit an individual's exercise capacity and increase the risk of
an adverse cardiovascular event during exercise. Cardiac autonomic neuropathy (CAN) may be
indicated by resting tachycardia (>100 beats per minute), orthostasis (a fall in
systolic blood pressure >20 mmHg upon standing), or other disturbances in autonomic
nervous system function involving the skin, pupils, gastrointestinal, or genitourinary
systems. Sudden death and silent myocardial ischemia have been attributed to CAN in
diabetes. Resting or stress thallium myocardial scintigraphy is an appropriate noninvasive
test for the presence and extent of macrovascular coronary artery disease in these
individuals. Hypotension and hypertension after vigorous exercise are more likely to
develop in patients with autonomic neuropathy, particularly when starting an exercise
program. Because these individuals may have difficulty with thermoregulation, they should
be advised to avoid exercise in hot or cold environments and to be vigilant about adequate
individual with diabetes for a safe and enjoyable exercise program is as important as
exercise itself. The young individual in good metabolic control can safely participate in
most activities. The middle-aged and older individual with diabetes should be encouraged
to be physically active. The aging process leads to a degeneration of muscles, ligaments,
bones, and joints, and disuse and diabetes may exacerbate the problem. Before beginning
any exercise program, the individual with diabetes should be screened thoroughly for any
underlying complications as described above.
recommendation for diabetic patients, as for nondiabetic individuals, is that exercise
includes a proper warm-up and cool-down period. A warm-up should consist of 510 min
of aerobic activity (walking, cycling, etc.) at a low-intensity level. The warm-up session
is to prepare the skeletal muscles, heart, and lungs for a progressive increase in
exercise intensity. After a short warm-up, muscles should be gently stretched for another
510 min. Primarily, the muscles used during the active exercise session should be
stretched, but warming up all muscle groups is optimal. The active warm-up can either take
place before or after stretching. Following the activity session, a cool-down should be
structured similarly to the warm-up. The cool-down should last about 510 min and
gradually bring the heart rate down to its pre-exercise level.
several considerations that are particularly important and specific for the individual
with diabetes. Aerobic exercise should be recommended, but taking precautionary measures
for exercise involving the feet is essential for many patients with diabetes. The use of
silica gel or air midsoles as well as polyester or blend (cotton-polyester) socks to
prevent blisters and keep the feet dry is important for minimizing trauma to the feet.
Proper footwear is essential and must be emphasized for individuals with PN. Individuals
must be taught to monitor closely for blisters and other potential damage to their feet,
both before and after exercise. A diabetes identification bracelet or shoe tag should be
clearly visible when exercising. Proper hydration is also essential, as dehydration can
affect blood glucose levels and heart function adversely. Exercise in heat requires
special attention to maintaining hydration. Adequate hydration prior to exercise is
recommended (e.g., 17 ounces of fluid consumed 2 h before exercise). During exercise,
fluid should be taken early and frequently in an amount sufficient to compensate for
losses in sweat reflected in body weight loss, or the maximal amount of fluid tolerated.
Precautions should be taken when exercising in extremely hot or cold environments.
High-resistance exercise using weights may be acceptable for young individuals with
diabetes, but not for older individuals or those with long-standing diabetes. Moderate
weight training programs that utilize light weights and high repetitions can be used for
maintaining or enhancing upper body strength in nearly all patients with diabetes.
AND TYPE 2 DIABETES
benefits of exercise for the patient with type 2 diabetes are substantial, and recent
studies strengthen the importance of long-term exercise programs for the treatment and
prevention of this common metabolic abnormality and its complications. Specific metabolic
effects can be highlighted as follows.
studies have demonstrated a consistent beneficial effect of regular exercise training on
carbohydrate metabolism and insulin sensitivity, which can be maintained for at least 5
years. These studies used exercise regimens at an intensity of 5080% Vo2max
three to four times a week for 3060 min a session. Improvements in HbA1c
were generally 1020% of baseline and were most marked in patients with mild type 2
diabetes and in those who are likely to be the most insulin resistant. It remains true,
unfortunately, that most of these studies suffer from inadequate randomization and
controls, and are confounded by associated lifestyle changes. Data on the effects of
resistance exercise are not available for type 2 diabetes although early results in normal
individuals and patients with type 1 disease suggest a beneficial effect.
appears that long-term programs of regular exercise are indeed feasible for patients with
impaired glucose tolerance or uncomplicated type 2 diabetes with acceptable adherence
rates. Those studies with the best adherence have used an initial period of supervision
followed by relatively informal home exercise programs with regular, frequent follow-up
assessments. A number of such programs have demonstrated sustained relative improvements
in Vo2max over many years with little in the way of significant complications.
of cardiovascular disease
In patients with
type 2 diabetes, the insulin resistance syndrome continues to gain support as an important
risk factor for premature coronary disease, particularly with concomitant hypertension,
hyperinsulinemia, central obesity, and the overlap of metabolic abnormalities of
hypertriglyceridemia, low HDL, altered LDL, and elevated FFA. Most studies show that these
patients have a low level of fitness compared with control patients, even when matched for
levels of ambient activity, and that poor aerobic fitness is associated with many of the
cardiovascular risk factors. Improvement in many of these risk factors has been linked to
a decrease in plasma insulin levels, and it is likely that many of the beneficial effects
of exercise on cardiovascular risk are related to improvements in insulin sensitivity.
has consistently been shown to be effective in reducing levels of triglyceride-rich VLDL.
However, effects of regular exercise on levels of LDL cholesterol have not been
consistently documented. With one major exception, most studies have failed to demonstrate
a significant improvement in levels of HDL in patients with type 2 diabetes, perhaps
because of the relatively modest exercise intensities used.
There is evidence
linking insulin resistance to hypertension in patients. Effects of exercise on reducing
blood pressure levels have been demonstrated most consistently in hyperinsulinemic
Many patients with
type 2 diabetes have impaired fibrinolytic activity associated with elevated levels of
plasminogen activator inhibitor-1 (PAI-1), the major naturally occurring inhibitor of
tissue plasminogen activator (TPA). Studies have demonstrated an association of aerobic
fitness and fibrinolysis. There is still no clear consensus on whether physical training
results in improved fibrinolytic activity in these patients.
accumulated suggesting that exercise may enhance weight loss and in particular weight
maintenance when used along with an appropriate calorie-controlled meal plan. There are
few studies specifically dealing with this issue in type 2 diabetes, and much of the
available data is complicated by the simultaneous use of unusual diets and other
behavioral interventions. Of particular interest are studies suggesting a disproportionate
effect of exercise on loss of intra-abdominal fat, the presence of which has been
associated most closely with metabolic abnormalities. Data on the use of resistance
exercise in weight reduction are promising, but studies in patients with type 2 diabetes
in particular are lacking.
Prevention of type 2
great deal of evidence has been accumulated supporting the hypothesis that exercise, among
other therapies, may be useful in preventing or delaying the onset of type 2 diabetes.
Currently, a large randomized prospective National Institutes of Health (NIH) study is
under way to clarify the feasibility of this approach.
AND TYPE 1 DIABETES
All levels of
exercise, 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 (note previous section). The ability to adjust the
therapeutic regimen (insulin and medical nutrition therapy) to allow safe participation
and high performance has recently been recognized as an important management strategy in
these individuals. In particular, the important role played by the patient in collecting
self-monitored blood glucose data of the response to exercise and then using these data to
improve performance and enhance safety is now fully accepted.
which can occur during, immediately after, or many hours after exercise, can be avoided.
This requires that the patient have both an adequate knowledge of the metabolic and
hormonal responses to exercise and well-tuned self-management skills. The increasing use
of intensive insulin therapy has provided patients with the flexibility to make
appropriate insulin dose adjustments for various activities. The rigid recommendation to
use carbohydrate supplementation, calculated from the planned intensity and duration of
exercise, without regard to glycemic level at the start of exercise, the previously
measured metabolic response to exercise, and the patient's insulin therapy, is no longer
appropriate. Such an approach not infrequently neutralizes the beneficial glycemic
lowering effects of exercise in patients with type 1 diabetes.
guidelines that may prove helpful in regulating the glycemic response to exercise can be
summarized as follows:
Metabolic control before exercise
- Avoid exercise if
fasting glucose levels are >250 mg/dl and ketosis is present or if glucose levels are
>300 mg/dl, irrespective of whether ketosis is present.
- Ingest added
carbohydrate if glucose levels are <100 mg/dl.
glucose monitoring before and after exercise
- Identify when changes in
insulin or food intake are necessary
- Learn the glycemic
response to different exercise conditions.
- Consume added
carbohydrate as needed to avoid hypoglycemia.
- Carbohydrate-based foods
should be readily available during and after exercise
diabetes is associated with an increased risk of macrovascular disease, the benefit of
exercise in improving known risk factors for atherosclerosis is to be highly valued. This
is particularly true in that exercise can improve the lipoprotein profile, reduce blood
pressure, and improve cardiovascular fitness. However, it must also be appreciated that
several studies have failed to show an independent effect of exercise training on
improving glycemic control as measured by HbA1c in patients with type 1
diabetes. Indeed, these studies have been valuable in changing the focus for exercise in
diabetes from glucose control to that of an important life behavior with multiple
benefits. The challenge is to develop strategies that allow individuals with type 1
diabetes to participate in activities that are consistent with their lifestyle and culture
in a safe and enjoyable manner.
the principles recommended for dealing with exercise in adults with type 1 diabetes, free
of complications, apply to children, with the caveat that children may be prone to greater
variability in blood glucose levels. In children, particular attention needs to be paid to
balancing glycemic control with the normalcy of play, and for this the assistance of
parents, teachers, and athletic coaches may be necessary. In the case of adolescents,
hormonal changes can contribute to the difficulty in controlling blood glucose levels.
Despite these added problems, it is clear that with careful instructions in
self-management and the treatment of hypoglycemia, exercise can be a safe and rewarding
experience for the great majority of children and adolescents with type 1 diabetes.
IN THE ELDERLY
accumulated suggesting that the progressive decrease in fitness and muscle mass and
strength with aging is in part preventable by maintaining regular exercise. The decrease
in insulin sensitivity with aging is also partly due to a lack of physical activity. Lower
levels of physical activity are especially likely in the population at risk for type 2
diabetes. A number of recent studies of exercise training have included significant
numbers of older patients. These patients have done well with good training and metabolic
responses, levels of adherence at least as good as the general population, and an
acceptable incidence of complications. It is likely that maintaining better levels of
fitness in this population will lead to less chronic vascular disease and an improved
quality of life.
The recent Surgeon
General's Report on Physical Activity and Health4 underscores the pivotal role
physical activity plays in health promotion and disease prevention. It recommends that
individuals accumulate 30 min of moderate physical activity on most days of the week. In
the context of diabetes, it is becoming increasingly clear that the epidemic of type 2
diabetes sweeping the globe is associated with decreasing levels of activity and an
increasing prevalence of obesity. Thus, the importance of promoting exercise as a vital
component of the prevention, as well as management of type 2 diabetes must be viewed as a
high priority. It must also be recognized that the benefit of exercise in improving the
metabolic abnormalities of type 2 diabetes is probably greatest when it is used early in
its progression from insulin resistance to impaired glucose tolerance to overt
hyperglycemia requiring treatment with oral glucose-lowering agents and finally to
with type 1 diabetes, the emphasis must be on adjusting the therapeutic regimen to allow
safe participation in all forms of physical activity consistent with an individual's
desires and goals. Ultimately, all patients with diabetes should have the opportunity to
benefit from the many valuable effects of exercise.
SH, Ruderman NB: Exercise and NIDDM (Technical Review). Diabetes Care 13:785789,
DH, Zinman B: Exercise in individuals with IDDM (Technical Review). Diabetes Care
Diabetes Association: Diabetes and exercise: the risk-benefit profile. In The Health
Professional's Guide to Diabetes and Exercise. Devlin JT, Ruderman N, Eds. Alexandria,
VA, American Diabetes Association, 1995, p. 34.
Department of Health and Human Services: Physical Activity and Health: A Report of the
Surgeon General. Centers for Disease Control and Prevention, National Center for
Chronic Disease Prevention and Health Promotion, Washington, DC, U.S. Govt. Printing
for Disease Control and Prevention and the American College of Sports Medicine: Physical
activity and public health: a recommendation. JAMA 273:402407, 1995.
College of Sports Medicine: The recommended quantity and quality of exercise for
developing and maintaining cardiorespiratory and muscular fitness in healthy adults
(Position Statement). Med Sci Sports Exercise 22:265274, 1990.
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