Look around your exercise floor. Although there are no outward or telltale signs, it is likely that several of your members or clients have some form of diabetes. It is also likely that many of these people either are unaware of their condition or have difficulty managing and regulating the disorder.
According to the Centers for Disease Control and Prevention (CDC), 20.8 million people who live in the United States currently have diabetes, accounting for 7% of Americans (CDC 2005). In fact, it is estimated that 6.2 million of these people have not been diagnosed with diabetes (CDC 2005).
Diabetes has an enormous medical and financial impact on our nation. Estimated diabetes costs in the U.S. in 2002 were $132 billion, of which $40 billion resulted from disability, work loss and premature death (CDC 2005). People with diabetes are at high risk for heart disease, stroke, blindness, and kidney and nervous-system diseases, which is why the medical costs of this condition are so high.
While it is outside of your scope of practice as a fitness professional to dispense medical advice to diabetic clients about specific issues such as blood glucose levels or medications, you are in a unique position to help. As the number of people with diabetes (or related conditions like hyperglycemia and hypoglycemia) continues to grow, it is imperative that fitness professionals have a practical understanding of how exercise benefits and affects these clients. This article outlines the mechanisms of diabetes; risk factors; signs and symptoms; complications of the condition; exercise considerations and contraindications; and recommendations for daily care.
When blood glucose levels begin to rise, beta cells in the pancreas secrete insulin, a hormone that regulates blood glucose, into the bloodstream. Subsequently, insulin receptors on the cell walls allow insulin (coupled with one or more glucose molecules) to enter the cells for metabolism. This series of events lowers serum blood sugar levels.
Type 1 diabetes occurs when the body cannot manufacture its own insulin because the beta cells of the pancreas that are responsible for insulin production have been destroyed. As a result, supplemental insulin must be injected or infused into the body to normalize glucose levels. As type 1 diabetes progresses, the number of insulin receptors diminishes slightly. This, in turn, decreases the ability of insulin and the glucose molecule pair to enter cells, even when the client is getting adequate supplemental insulin. Over time, the person’s blood glucose levels become even more difficult to stabilize and manage.
Unlike type 1 diabetes, which results from an inability to produce insulin, type 2 diabetes occurs when the body’s cells are unable to utilize insulin properly; this inability is known as insulin resistance. Over decades, the pancreas gradually loses its ability to produce insulin, and the number of insulin receptors on the cell walls markedly decrease, especially in people who are inactive and overweight or obese.
Gestational diabetes mellitus (GDM) is a condition that occurs in some women during pregnancy. GDM is a form of insulin resistance; however, the exact cause is unknown. It is theorized that hormones in the placenta may block the action of the mother’s insulin (American Diabetes Association 2007). Because diet management alone does not improve glucose control in women with GDM, exercise is key to controlling blood glucose levels in women with this condition.
It is also possible for diabetes to result from causes such as surgery or illness. (Other conditions that are related to diabetes, such as exercise-induced hypoglycemia and hyperglycemia, will be discussed later.)
Type 1 diabetes currently accounts for 5%–10% of all diagnosed cases of diabetes (CDC 2005). Although it can occur at any age, type 1 diabetes is diagnosed mostly in children and in young adults. The factors that put people at risk of developing type 1 diabetes include autoimmune disorders, genetic traits and environmental conditions.
Presently, there is no known way to prevent or cure type 1 diabetes. However, it can be managed with some crucial steps. First and foremost, it is imperative that individuals with type 1 diabetes take precautions to avoid extreme blood sugar fluctuations by judiciously monitoring their blood glucose levels and by being vigilant about carbohydrate counting and ingestion. People with type 1 diabetes should receive nutrition counseling from a registered dietitian (RD) and/or a certified diabetes educator to learn about macronutrient and medication impact on blood sugar levels.
The signs and symptoms of type 1 diabetes include increased thirst and sudden weight loss (American Diabetes Association 2007). Type 1 diabetes is most often confirmed by performing a fasting plasma glucose (FPG) test, which involves drawing a blood sample after an 8-hour fasting period; the FPG test measures the amount of glucose present in the blood. An FPG score of 126 milligrams per deciliter (mg/dl) or higher is considered a positive result for type 1 diabetes.
Once diagnosed with the condition, people with type 1 diabetes undergo routine blood tests to measure glycosylated hemoglobin (HbA1c) levels. HbA1c is a form of hemoglobin that has been altered by high levels of blood glucose. This simple test measures the blood glucose levels over the preceding 2–3 months and gives an indication for blood glucose control. HbA1c levels lower than 7.0% are desirable (American Diabetes Association 2007).
Previously called non-insulin-dependent diabetes or adult-onset diabetes, type 2 diabetes mostly afflicts older people, although more and more children and adolescents are being diagnosed with the condition each year. This should come as no surprise, given that type 2 diabetes is associated with obesity and physical inactivity, both of which are on the rise in younger people. Other risk factors for type 2 diabetes include a family history of the condition, impaired glucose metabolism, ethnicity and race. African Americans, Hispanic/Latino Americans, American Indians, some Asian Americans and some Native Hawaiians and other Pacific Islanders are at particularly high risk for type 2 diabetes and its complications (CDC 2005). (See sidebar “Risk Factors for Type 2 Diabetes,” below.) Type 2 diabetes accounts for 90%–95% of all diagnosed cases of diabetes (CDC 2005).
Measuring FPG is also the preferred way to test for type 2 diabetes, with a score of 126 or higher leading to a positive diagnosis. If the FPG score is 100 mg/dl to 125 mg/dl, the person is diagnosed as having impaired fasting glucose (IFG) levels, which is officially known as prediabetes (American Diabetes Association 2007).
The good news is that the progression from prediabetes to type 2 diabetes is not inevitable. Studies have shown that if people with prediabetes lose weight and increase their physical activity, they can prevent or delay diabetes and even return their blood glucose levels to normal (American College of Sports Medicine [ACSM] 2006).
The bad news is that prediabetes has been identified as a major cause of metabolic syndrome, a cluster of different risk factors that are associated with cardiovascular disease (CVD). Other risk factors included in metabolic syndrome are obesity, hypertension, low high-density lipoprotein (HDL) cholesterol levels and elevated plasma triglyceride levels.
By the age of 45, individuals should undergo screening to detect prediabetes or type 2 diabetes. Diabetes screening is especially important for people with a body mass index (BMI) of 25 or higher (American Diabetes Association 2007). Screening should also be considered for overweight or obese people under age 45 years of age if they have another risk factor for diabetes (American Diabetes Association 2007).
Studies have revealed a strong relationship between both types of diabetes and CVD. Adults with diabetes are two to four times more likely to experience a stroke or die from heart disease than their counterparts who do not have the condition (CDC 2005). Together, heart disease and stroke account for about 65% of deaths in people with diabetes. Approximately 73% of adults with diabetes have blood pressure ≥ 130/80 millimeters of mercury (mm Hg) or use prescription medications for high blood pressure (CDC 2005).
Chronically high levels of glucose in the blood predisposes a person with diabetes to CVD. Elevated blood sugar levels modify plasma low-density lipoprotein (LDL) cholesterol. Because this modified version of LDL cholesterol is more readily taken up by cells in the arterial walls, there is a higher likelihood of developing arterial plaque and ultimately CVD.
As noted, prediabetes is a major cause of metabolic syndrome, which, in turn, is associated with CVD. Individuals with three or more of the risk factors for metabolic syndrome have a significantly increased risk of dying from CVD.
In addition to increasing the risk of heart disease, diabetes can have other negative effects on the body. Diabetes is the leading cause of new cases of blindness among adults 20–74 years old and the number-one cause of kidney failure (CDC 2005). In addition, roughly 60%–70% of people with diabetes have mild to severe forms of nervous-system damage (CDC 2005). The results of such damage include impaired sensation or pain in the feet or hands; slowed digestion of food in the stomach; carpal tunnel syndrome; and other neurological problems.
Other complications of both types of diabetes include amputations; tooth and gum disease; complications during pregnancy; and increased susceptibility to many other diseases, such as pneumonia or influenza.
Regulating blood glucose levels and carefully monitoring carbohydrate consumption can help clients with type 1 and type 2 diabetes manage their condition and reduce their risk for future complications.
Blood glucose levels should be measured at scheduled intervals using a glucometer, which measures blood sugar levels, along with a glucometer test strip and lancet. A baseline blood glucose measurement, known as fasting blood glucose, should be taken upon waking and before eating. In addition, clients with diabetes should measure their blood glucose levels before and 2 hours after meals, as well as before, during and after exercise, until levels are considered stable. Clients new to exercise should check their blood sugar levels more frequently, to ensure that blood glucose levels are maintained. Optimal blood glucose levels obtained before meals should be in the range of 90–130 mg/dl, while levels taken 1–2 hours after beginning a meal should be lower than 180 mg/dl (American Diabetes Association 2007).
Carbohydrate intake can have a dramatic effect on blood glucose levels. Individuals with either type 1 or type 2 diabetes must monitor their carbohydrate intake carefully by counting carbohydrates, following an exchange plan or using experience-based estimates to help achieve glycemic control. (An exchange plan is a diet regimen in which foods within the same food group are exchanged in order to maintain or stabilize blood glucose levels.) Refined simple carbohydrates, such as white bread, white rice, pasta and sugary drinks, can be used to raise blood glucose levels both dramatically and immediately. These kinds of carbohydrates are recommended for clients who experience temporary hypoglycemia or who need to raise blood glucose levels quickly. Complex carbohydrates, such as whole-grain bread and whole-grain cereals, are less likely to produce dramatic fluctuations in blood glucose and thus are not as effective for quickly raising blood glucose levels.
Fortunately, the majority of the clients you will encounter while training will not require special care for diabetes. However, some clients may have difficulties with vision and may need assistance setting up or handling fitness equipment. Similarly, clients with active retinopathy (damage to the blood vessels in the eye) should avoid strenuous activity and any exercise that involves straining, jarring or Valsalva-like maneuvers.
Clients who experience pain or impaired sensation in their fingers or feet may need you to provide alternatives to handheld weights and treadmills. Individuals with limited capacity for exercise because of obesity and severe deconditioning will require your patience and inspiration. Some clients will come to you with medical restrictions resulting from cardiac complications; if you cannot meet the needs of these people, you must use your professional discretion and refer them to other health professionals.
Most clients with diabetes are prescribed several medications to help manage their condition. The most widely prescribed medicines for diabetes are metformin, glyburide, chlorpropamide and glypizide, which decrease glucose produced by the liver and stimulate insulin production by the pancreas. Generally speaking, diabetic medications have not been shown to affect exercise tolerance, electrocardiographic data, blood pressure or heart rate. However, clients who take a class of drugs called sulfonylureas, which include glyburide, chlorpropamide and glypizide, may be less likely to achieve higher workloads than nonusers.
Exercise is an established adjunctive therapy in diabetes management. Regular exercise helps control blood glucose levels in clients with type 2 diabetes and in women with GDM in the following ways:
• It increases glucose uptake by the cells.
• It improves insulin sensitivity by improving glucose metabolism.
• It reduces the risk of CVD.
Unfortunately, few studies to date have found that exercise helps control blood glucose levels in clients with type 1 diabetes. This is probably because people with type 1 diabetes have to increase their carbohydrate intake to avoid exercise-induced hypoglycemia. The effects of eating more and the resultant elevated blood glucose levels counteract the potential improvement in HbA1c. However, clients with type 1 diabetes do see improvements in insulin sensitivity, glucose metabolism and CVD risk factors after establishing a regular exercise program (ACSM 2001).
Many type 1 diabetics use an insulin pump to deliver a calculated dose of insulin at designated intervals. Each person’s pump, which is the size of a deck of cards and can be worn on a belt at the waist, is programmed to his or her individual needs. The pump delivers a continuous supply of insulin and, when necessary, a bolus to accommodate the carbohydrate load of a meal. Other type 1 diabetics use insulin syringes to inject insulin one or more times a day. A pump is more effective at controlling blood glucose levels because it can deliver very small amounts of insulin, which is not possible with a syringe. With physician approval, most users can safely disconnect their pumps for 1–2 hours. Clients need to inspect their pump insertion sites before and after exercise and must be prudent about changing sites every 2–3 days to prevent infection.
For insulin pump users involved with aquatic exercise, waterproof models are available; however, some health professionals recommend removing pumps before water exercise to prevent damage. Protective cases for pumps are available for those who engage in light-contact sports. Because pumps can become dislodged from their insertion sites, wearing a pump while engaged in high-contact activity is not recommended.
Clients with both types of diabetes can suffer from exercise-induced hypoglycemia, a condition that can cause undue anxiety or shakiness; changes in gait and coordination; inability to think or see clearly; excessive perspiration; dizziness; nausea; loss of consciousness; and even coma. Exercise-induced hypoglycemia is caused by a lack of glucose in the blood.
To prevent exercise-induced hypoglycemia, clients should measure their blood glucose levels before exercise, during exercise (if it lasts longer than 30 minutes) and again 15 minutes after exercise, to detect low blood glucose levels. Clients should also avoid exercise at peak time of insulin, the period in which insulin is most effective at lowering blood glucose levels. Instead, clients should be encouraged to exercise when insulin effects are low and blood glucose is on the rise (i.e., shortly after eating) (Funnell et al. 2004).
Clients with exercise-induced hypoglycemia may also benefit from eating a carbohydrate snack during their workouts. The amount and timing of the snack should depend on the intensity of the exercise, its duration, the pre-exercise blood glucose level and the individual’s response to exercise. (It is the available glucose in food rather than the amount of available carbohydrates that acutely affects blood glucose levels.) One rule of thumb is that if a client’s blood glucose level falls below 100 mg/dl, a carbohydrate snack should be eaten. (See sidebar “Carbohydrate Supplementation & Exercise Intensity,” below.) After eating the snack, the client should wait 15 minutes, then test the blood glucose level again and not return to exercising until the level is at least 100 mg/dl. Adding fat to the carbohydrate may prolong the glycemic response.
Although it is more common in type 1 diabetics, any client with diabetes can experience hypoglycemia up to 48 hours after an exercise session, so it is vital to monitor glucose levels frequently after a workout. Postexercise, late-onset hypoglycemia (PEL) is defined as a reaction more than 4 hours after exercise. Clients with diabetes should never exercise at night, because nocturnal hypoglycemia can result. Blood glucose responses to exercise in lean clients with type 2 diabetes are highly variable and less predictable than those that occur in their obese counterparts (ACSM 2007).
Hyperglycemia, defined as having blood glucose levels greater than 300 mg/dl, results when the body does not have enough glucose to meet its metabolic demands. This condition causes the body to break down proteins and fats in order to produce energy, which results in the production of compounds called ketones. The signs and symptoms of acute hyperglycemia include increased thirst; increased hunger; increased urine output; blurred vision; fatigue; and the presence of ketones in the urine as detected by a dipstick test (Wikipedia 2007). Ketoacidosis is the term used to describe an excessive formation or secretion of ketones in the body.
Fortunately, the incidence of hyperglycemia in the fitness setting is uncommon. However, ACSM recommends that clients should not exercise if their blood glucose levels exceed 250 mg/dl and ketones are detected in the urine; ACSM also recommends that clients use caution when working out if their blood glucose levels reach or exceed 300 mg/dl and no ketones are present (ACSM 2006). It is prudent to withhold exercise if ketoacidosis is detected in the dipstick test, because exercise can worsen hyperglycemia (American Diabetes Association 2007). According to ACSM guidelines, clients with blood glucose levels greater than 400 mg/dl should not participate in any form of exercise (ACSM 2001).
Developing a safe and effective exercise program for people living with diabetes can be a challenge but one that is worthwhile. As a fitness professional, you have the unique opportunity to educate, motivate and guide your clients toward a lifestyle that includes regular blood glucose monitoring, proper diet and regular physical activity.
- history of physical inactivity
- family history of diabetes
- ethnicity/race (e.g., African Americans, Hispanic/Latino Americans, American Indians, some Asian Americans and some Native Hawaiians and other Pacific Islanders)
- diagnosis of gestational diabetes or delivery of a baby weighing more than 9 pounds
- high blood pressure (> 140/90 mm Hg)
- HDL level < 35mg/dl and/or a triglyceride level > 250 mg/dl
- diagnosis of prediabetes
- polycystic ovarian syndrome
- history of vascular disease, such as heart disease
Source: American Diabetes Association. 2007. Standards of medical care in diabetes—2007 Position Statement. Diabetes Care, 30 (Suppl. 1).
Copy and distribute this checklist to clients who have been diagnosed with type 1 or type 2 diabetes.
- Get physician clearance before starting any exercise program.
- Test your blood glucose level before exercise; during exercise (if you are new to exercise or the session lasts longer than 30 minutes); and after exercise.
- Follow these general guidelines for a safe exercise session: warm up and cool down, stretch, adhere to your target heart rate zone and drink plenty of water. Wear well-fitting, well-cushioned, supportive shoes, as well as polyester or blended socks, to keep your feet dry and to minimize trauma to the feet.
- Avoid strenuous, high-impact or static activity unless specifically approved by your physician.
- Carry a carbohydrate snack with you.
- Wear identification that tells others you have diabetes.
- Know and monitor the signs of exercise-induced hypoglycemia.
- Do not exercise if your blood glucose level is < 70 mg/dl or
> 250 mg/dl and you have ketones in your urine. Use caution if your blood glucose level is > 300 mg/dl, whether ketones are present or not.
- If you have a condition related to diabetes, such as autonomic neuropathy, peripheral neuropathy, neuropathy or retinopathy, always get approval for exercise from your physician prior to starting a fitness program; these conditions require specific guidelines and strict limitations. (Fitness professionals: Be sure to ask clients if any of these conditions apply!)
Bob Edwards, a 52-year-old man, is a new member at your facility. He was recently diagnosed with type 2 diabetes, and his doctor has advised him to lose 40 pounds by improving his diet and becoming more physically active; he has been approved to start a regular exercise program. Bob has been seeing both a registered dietitian and a certified diabetes educator for guidance with lifestyle modification. Bob is new to exercise and comes to you seeking exercise instruction and guidance on how to set exercise limits.
During his initial visit to your facility, you meet with Bob to collect relevant information. Bob weighs 238 pounds, and his BMI is 32, which means he is considered obese. His blood pressure is slightly elevated (136/86 mm Hg), but he tells you he does not have heart disease or any other serious or orthopedic conditions that might impact his exercise program. He states that his recent exercise stress test was normal. Bob reports taking both metformin and a sulfonylurea to help control his blood glucose levels.
As a fitness professional, you need to set appropriate limits for intensity, duration and frequency of exercise for this client. ACSM recommends using a target heart rate zone of 50%–90% of maximum or 50%–80% of VO2 reserve or heart rate reserve (ACSM 2006). Exercise sessions should last 20–60 minutes and should include 5- to 10-minute warm-up and cool-down periods, as well as moderate-level resistance training (40%–60% 1RM). You should advise Bob to accumulate between 1,000 and 2,000 kilocalories of physical activity per week to reach his weight loss goal (ACSM 2006). Also advise him to exercise at least 3–5 days per week (ACSM 2001).
After 2 weeks of regular exercise at your facility, Bob reports that he has been having postexercise signs and symptoms (e.g., dizziness and excess perspiration) of exercise-induced hypoglycemia. He denies overexerting and claims to be adhering to the levels and recommendations you set in your initial meeting. When you ask Bob about his medication regimen, he says that he takes both medications in the morning about 2 hours before he comes to exercise. Because the medications peak at the time he is completing his exercise routine, Bob’s blood glucose levels are low. Tell Bob to speak with his physician about the timing and dosing of his medications. Insist that he make no medication changes without first speaking with his doctor.
One week after Bob has spoken to his doctor, you follow up with him. He reports that the doctor reduced the dosage of the medications, and the episodes of hypoglycemia have been eliminated. Now, 3 months after Bob’s initial visit to your facility, he is adhering to your guidelines and reports that he feels less fatigued and stronger—plus, he has lost 10 pounds in the process!
|Intensity of Activity||Blood Glucose Level||Recommended Carbohydrate Intake||Suggestions|
|light||< 100 mg/dl||10-15 g per hour||1 fruit serving or 1 bread serving (1/2 cup orange juice or 1/4 bagel)|
|light||≥ 100 mg/dl||none|
|moderate||< 100 mg/dl||
15–30 g carbohydrate before exercise, then 10–15 g per 30–60 minutes of exercise
|1 milk serving and 1 fruit serving, or 1 milk serving and 1 bread serving (1 cup plain yogur and 1/2 banana, or cereal and 1 cup milk)|
|moderate||100-180 mg/dl||10-15 g per 30 minutes of exercise||1 fruit serving or 1 bread serving (1/2 banana or 8 saltine crackers)|
|strenuous||< 100 mg/dl||about 45 g carbohydrate; test blood glucose often||2 bread servings with either 1 milk serving or 1 fruit serving (2 slices of toast with either 1 cup fat-free milk or 1 small orange)|
|strenuous||100-180 mg/dl||30-50 g carbohydrate (depends on intensity and duration)||1 milk serving and 1 bread serving (1 slice bread and 1 cup milk) or 1 fruit serving and 1 bread serving|
|strenuous||180-300 mg/dl*||15-30 g carbohydrate per 30-60 minutes of excercise||1 milk serving and 1 fruit serving, or 1 milk serving and 1 bread serving (1 cup plain yogurt and 1/2 banana, or cereal and 1 cup milk)|
Light activity is defined as activity that lasts less than 30 minutes; elevates heart rate slightly, but does not bring on dyspnea; and requires approximately 2–4 METs (i.e., walking or biking leisurely, doing light housework).
Moderate activity is defined as activity that lasts 30–60 minutes; involves noticeable heavier breathing, with a pulse rate increase to more than 100 beats per minute (bpm); and requires approximately 4–7 METs (i.e., gardening, swimming at moderate level).
Strenuous activity is defined as activity that involves rapid breathing, with a pulse rate between 125 and 160 bpm, and requires approximately 7–9 METs (i.e., ice hockey, basketball, strenuous swimming).
*Check for ketones if blood glucose is over 250 mg/dl.
Adapted from Funnell, M., et al. 2004. Life With Diabetes: A Series of Teaching Outlines by the Michigan Diabetes Research and Training Center. (3rd ed.) Alexandria, VA: American Diabetes Association.
Check out these resources for more information on diabetes:
American College of Sports Medicine (ASCM) 2000.
Exercise and Type 2 Diabetes: Position Stand. Available at www.acsm-msse.org/pt/pt-core/templatejournal/msse/
American College of Sports Medicine (ASCM). 2005. ACSM’s Resource Manual for Guidelines for Exercise Testing and Prescription (5th ed.). Baltimore: Lippincott Williams & Wilkins.
American College of Sports Medicine (ASCM). 2006. ACSM’s Guidelines for Exercise Testing and Prescription (7th ed.). Baltimore: Lippincott Williams & Wilkins.
American Diabetes Association. 2002. Diabetes Mellitus and Exercise: 2002 Position Statement. Diabetes Care, (25), S64. www.diabetes.org.
Ruderman, N., and Devlin, J. (Eds.).1995. The Health Professional’s Guide to Diabetes and Exercise. American Diabetes Association.
Peggy Kraus, MA, RCEP, is an ACSM-registered clinical exercise physiologist who works in the CardioPulmonary Rehab & Fitness Center at Southampton Hospital in Southampton, New York. She educates diabetic patients about the benefits of exercise and weight control and encourages them to achieve optimal blood glucose control.
American College of Sports Medicine (ACSM). 2001. ACSM’s Resource Manual for Guidelines for Exercise Testing and Prescription (4th ed.). Baltimore: Lippincott Williams & Wilkins.
American College of Sports Medicine (ACSM). 2006. ACSM’s Guidelines for Exercise Testing and Prescription (7th ed.). Baltimore: Lippincott Williams & Wilkins.
American College of Sports Medicine (ACSM). 2007. ACSM Exercise and Type 2 Diabetes: Position Stand. www.acsm-msse.org/pt/pt-core/template-journal/msse/media/0700.pdf; retrieved June 19, 2007.
American Diabetes Association. 2007. Standards of medical care in diabetes—2007 Position Statement. Diabetes Care, 30 (Suppl. 1).
Centers for Disease Control and Prevention (CDC). 2005. National diabetes fact sheet: General information and national estimates on diabetes in the United States. Atlanta: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention.
Funnell, M., et al. 2004. Life With Diabetes: A Series of Teaching Outlines by the Michigan Diabetes Research and Training Center (3rd ed.). Alexandria, VA: American Diabetes Association.
Wikipedia. 2007. Ketoacidosis facts. http://en.wikipedia.org/wiki/Ketoacidosis; retrieved June 19, 2007.