Diabetes & Exercise: What Every Fitness Professional Should Know

Exercise is a safeguard against the disease, especially type 2.

By IDEA Authors
Aug 15, 2014

Diabetes affects nearly one-tenth of the U.S. population—a widening epidemic with more than 5,000 new cases per day and an economic cost of $245 billion per year (ADA 2013).

These alarming statistics and their worrisome health consequences (see Figure 1) make it imperative for us to understand how to manage or prevent diabetes safely and effectively. Fortunately, research demonstrates that regular exercise may combat some of the deleterious effects of diabetes and can sometimes prevent it from striking high-risk individuals (Colberg et al. 2010). Colberg et al. say studies find that exercise supervised by qualified trainers has the greatest impact on controlling blood glucose—the pivotal factor in all diabetes cases. That’s why it’s so important for certified exercise professionals to take the lead in educating clients on the risks, management and deterrence of diabetes.

Historical Roots of Diabetes and Insulin

The combined symptoms of rapid weight loss, extreme thirst and constant urination have confronted medical practitioners for more than 3,000 years. The term diabetes, Greek for “to pass through,” was first used by Apollonius of Memphis in 230 bc (Zajac et al. 2010). Aretaeus of Cappadocia, a Greek physician in the second century ad, helped to clarify diabetes symptoms (excessive thirst and urination; also see Figure 2) and outcomes (shorter life) (Zajac et al. 2010).

Attempts to treat diabetes failed for millennia, though doctors did come to understand that the disease had something to do with blood glucose. The biggest breakthroughs happened after Frederick Grant Banting and Charles Best from Canada were credited with discovering the efficacy of insulin in 1921, leading to many treatment and research advances (Zajac et al. 2010). Banting and Best created a pancreatic extract that improved the condition of diabetic dogs. In 1922, the two scientists injected the first human subject, a 14-year-old diabetic boy, with a variety of the extract that came to be called insulin. Within 24 hours, the boy’s blood glucose plunged from a dangerously high 520 milligrams per deciliter to 120 mg/dL, which is just above normal in nondiabetics (Zajac et al. 2010). That same year, insulin was purified and commercially produced by Eli Lilly Company, which worked closely with Banting and Best (Zajac et al. 2010).

What Are the Varieties of Diabetes?

Diabetes has three main types: type 1, type 2 and gestational. Prediabetes is not a distinct type, though it is sometimes characterized as a precursor that indicates an increased risk of developing type 2 diabetes.

Type 1

Type 1 diabetes, formerly called juvenile-onset diabetes, accounts for 5%–10% of all diabetes cases (Colberg et al. 2010). Type 1 is an autoimmune disease where the body’s defense system mistakenly attacks the pancreatic islet beta cells that produce insulin (IDF 2014), totally depleting the body’s insulin secretions. To survive, type 1 diabetics need daily insulin injections or an insulin pump to control their blood glucose levels. Type 1 diabetes is usually diagnosed in children or young adults, yet it may affect people at any age. A type 1 diabetes intervention is built on creating a healthy lifestyle with increased physical activity, a healthy diet, weight control and proper insulin medication.

Type 2

Type 2 diabetes, formerly called non-insulin-dependent diabetes or adult-onset diabetes, accounts for about 90% of diabetes cases (IDF 2014). It is described as a condition of insulin resistance, which means the body is misusing the insulin the pancreas produces (see “What Is the Pathophysiology of Type 2 Diabetes?”). As blood glucose levels rise in a type 2 patient, the body’s cells become unable to take up the extra glucose. A diagnosis of type 2 diabetes may occur at any age. Insulin resistance and type 2 diabetes are highly associated with overweight and/or obesity (IDF 2014). People with type 2 diabetes can manage their condition by exercising, following a healthy meal plan, losing excess weight and taking oral medications (Colberg et al. 2010).

Gestational

Gestational diabetes mellitus (GDM) is a form of diabetes in which high blood glucose levels develop during pregnancy. It occurs once in every 25 pregnancies worldwide, with complications to both mother and baby (IDF 2014). GDM usually disappears after pregnancy, but women with GDM and their children have an increased risk of developing type 2 diabetes later in life. Furthermore, about half of women with a history of GDM develop type 2 diabetes within 5–10 years after delivery (IDF 2014).

Prediabetes

People with prediabetes have impaired fasting glucose or impaired glucose tolerance—or both. With the former, the fasting blood sugar level is 100–125 mg/dL after an overnight fast—higher than normal (75–100 in nondiabetics), but too low to be classified as diabetes. With the latter, the blood sugar level is 140–199 mg/dL after a 2-hour oral glucose tolerance test, which is also above normal but not high enough to be classified as diabetes (ADA 2014a).

What Is the Pathophysiology of Type 2 Diabetes?

Because diet and exercise can play a large role in treating or preventing type 2 diabetes, it’s helpful to understand the role of blood glucose regulation in the hormonal pathophysiology that leads to this variety of the disease. Glucose, a simple sugar from carbohydrates, is a primary fuel that the body’s cells break down to liberate energy for life, work and exercise. The body stores glucose in the form of glycogen in muscle and the liver, and regulates glucose levels with insulin and glucagon, two hormones secreted by the pancreas.

Insulin and glucagon are made by specialized islets of Langerhans cells, named after the German physician Paul Langerhans, who described them in 1869 (Ruder 2011). Islet beta cells create insulin, which helps the body uptake glucose from the blood (Ruder 2011). Islet alpha cells produce glucagon, which stimulates the liver to raise glucose levels if they are low (Ruder 2011). Normal glucose regulation involves a complex interplay of insulin, glucagon and circulating glucose to maintain a homeostatic balance (see Figure 3).

Normally, insulin binds to insulin receptors on the muscle cells that signal glucose transporters known as GLUT4 proteins to shuttle glucose into the cells (Ploug & Ralston 2002) (see Figure 4). Disruptions to this process prevent glucose from being deposited into the cells, which causes blood glucose levels to rise—the condition called insulin resistance (see Figure 4).

High blood glucose levels cause the pancreas to produce more insulin, which creates an excess in the blood stream. Eventually, type 2 diabetes presents if nothing is done to rectify this impaired metabolic imbalance of elevated glucose and insulin.

Muscle Cell Uptake

What Are the Main Risk Factors for Developing Type 2 Diabetes?

The American Diabetes Association (ADA 2014a) has established the following risk factors for type 2 diabetes:

  • adults who are overweight (BMI ≥25 kg/m2) and have additional risk factors from this list
  • physical inactivity
  • first-degree relative with diabetes
  • high-risk race/ethnicity (such as African American, Latino, Native American, Asian American, Pacific Islander)
  • women who have delivered a baby weighing more than 9 pounds or were diagnosed with gestational diabetes
  • hypertension (140/90 mm Hg or on therapy for hypertension)
  • HDL cholesterol level <35 mg/dL (0.90 mmol/L) and/or a triglyceride level >250 mg/dL (2.82 mmol/L)
  • women with polycystic ovarian syndrome
  • A1C ≥5.7%, impaired glucose tolerance or impaired fasting glucose on previous testing
  • other clinical conditions associated with insulin resistance (such as severe obesity and acanthosis nigricans—a skin disorder in which there is darker, thick, velvety skin in body folds)
  • history of cardiovascular disease

Note: In the absence of the above criteria, testing for diabetes should begin at age 45. If results are normal, testing should be repeated at least every 3 years, with consideration of more frequent testing depending on initial results and risk status (those with prediabetes should be tested yearly).

Assessment Criteria

How Is Diabetes Diagnosed?

Healthcare professionals use several tests based on plasma glucose criteria to diagnose prediabetes or diabetes. The fasting blood glucose test measures blood glucose after an 8-hour fast. The oral glucose tolerance test measures blood glucose 2 hours after consumption of a glucose-laden drink (75 g of glucose). One of the preferred tests measures hemoglobin A1C, which reflects average blood glucose over 2–3 months.

If a test result exceeds the diagnostic cut point, the test is repeated to rule out lab error, unless the diagnosis is clear, as may happen, for example, when a person displays classic symptoms of hyperglycemia (ADA 2014b). If a person’s results are above the criterion level in one test and normal in another, the test with the elevated result is repeated. Criteria levels for normal, prediabetes and diabetes are shown in Figure 5.

What Are the Management Goals for Type 2 Diabetics?

The major focus of managing type 2 diabetes is to protect against the long-term complications of the disease. Since insulin resistance is a key player in type 2 diabetes, which also influences cardiovascular disease, interventions focus on improving insulin sensitivity by enhancing glucose uptake. Lifestyle interventions, healthy eating, exercise, weight loss, self-care behaviors and oral medications are all considered (ADA 2014a).

Centerpieces of most type 2 diabetes management plans are exercise and diet, because they improve glucose metabolism, blood lipids and blood pressure abnormalities, and contribute to sustained weight loss (Colberg et al. 2010). Colberg et al. propose that medications should complement lifestyle improvements, not replace them.

What Are the Metabolic Effects of Exercise?

During exercise, the most important factors influencing fuel use are intensity and duration (Colberg et al. 2010). Muscle glycogen provides plenty of fuel for working muscles, but as those stores are depleted with increased intensity, muscles increase their uptake and utilization of circulating blood glucose and free fatty acids (Colberg et al. 2010).

The breakdown of stored glycogen is called glycogenolysis. Even in the presence of type 2 diabetes, blood glucose uptake by working muscles is normal because muscle contractions trigger GLUT4 transporters (also called translocators) (Colberg et al.
2010). Colberg and colleagues note that this independent muscle contraction–mediated uptake of blood glucose remains elevated for several hours, a very noteworthy benefit of exercise. Type 2 diabetes impairs insulin-stimulated GLUT4 translocation, which is why exercise is so vital. Importantly, resistance exercise and aerobic training increase GLUT4 abundance and blood glucose uptake (Colberg et al. 2010).

Recent research has shown that resistance exercise is as important as, and perhaps even more important than, aerobic training in diabetes management (Colberg et al. 2010). An increase in muscle mass resulting from resistance training can contribute profoundly to glucose uptake. However, a combination of aerobic exercise and resistance training is more effective for blood glucose control than either type of exercise alone (Colberg et al. 2010).

Physical activity of any intensity will provide acute effects by enhancing blood glucose uptake for glycogen synthesis and by stimulating fat oxidation (breakdown) in muscle (Colberg et al. 2010). Colberg and colleagues add that current research suggests that longer-duration and more-intense training sessions elicit the best results for blood glucose reductions.

In educating clients on preventing or managing diabetes, personal trainers need to stress the importance of aerobic exercise and resistance training, because both improve long-term insulin action, blood glucose control and fat oxidation in muscle (Colberg et al. 2010). Trainers should encourage clients to achieve higher levels of physical fitness and physical activity, as they are associated with lower rates of cardiovascular disease and mortality in both healthy and diabetic patients (Colberg et al. 2010).

Preexercise Evaluation

Diabetes-related health complications like cardiovascular disease, hypertension, neuropathy (nerve damage) and microvascular changes (i.e., changes to small blood vessels) can complicate safe exercise participation. For those planning low-intensity activity, such as walking, conducting an exercise stress test before starting is unnecessary. Requiring these people to do a stress test may discourage them from participating (Colberg et al. 2010).

Sedentary and older diabetics who plan to engage in activities more intense than brisk walking should be assessed before they start. Conditions of concern include uncontrolled hypertension, severe autonomic neuropathy (damage to nerves that control body functions such as blood pressure, heart rate, sweating, bowel and bladder emptying, and digestion), severe peripheral neuropathy (affecting nerves outside the brain and spinal cord), history of foot lesions, and unstable proliferative retinopathy (growth of new blood vessels on retina that can bleed).

The client’s age and previous physical activity level should be considered. People with complications may require a more thorough evaluation by a qualified health practitioner.

Summary Thoughts

Exercise professionals can make a major difference in helping clients prevent or manage diabetes. Colberg et al. (2010) stress that combining aerobic exercise with resistance training is the best way to enhance blood glucose control. The authors also recommend that clients increase their daily unstructured movement (spontaneous physical activity), as this will increase caloric expenditure and contribute to weight loss goals.

Personal trainers are advised to help their diabetic clients monitor blood glucose before, during and after exercise. With higher-intensity exercise programs, which elevate metabolism for hours after exercise, clients with diabetes are also encouraged to check their blood glucose a few hours after exercise (and even before going to sleep) and to have a snack if glucose falls below 100 mg/dL. Cardiovascular exercise and resistance training are persuasive pillars for the prevention and treatment of type 2 diabetes. Let’s combat this disease now!

10 Questions & Answers on Diabetes
  1. Are older people more likely to have diabetes?
    Yes, approximately 27% of people aged 65 or older have diabetes, compared with about 11% of people aged 20 or older (Ruder 2011).
  2. What countries around the world have the most people (20-79 years old) with diabetes?
    According to the IDF (2014), countries that have the most people with diabetes are (in order) China, India, United States, Brazil and the Russian Federation.
  3. What and when is World Diabetes Day?
    World Diabetes Daywas created in 1991 by the International Diabetes Federation and the World Health Organization. The United Nations passed a resolution in 2007 declaring November 14 (birthday of Frederick Banting, co-developer of insulin) as World Diabetes Day. On this day, U.N. member countries promote diabetes awareness with 5 radio and television programs, sports events, free screenings for diabetes, public information meetings, events for children, and walks, runs and more.
  4. What do I do if a diabetic client is experiencing hypoglycemia?
    Hypoglycemia is defined as blood glucose below 70 mg/dL aDa 2014b). Symptoms can include shakiness, nervousness, anxiety, sweating, chills, irritability, confusion, rapid resting heartbeat, light-headedness, dizziness, hunger, nausea, blurred/ impaired vision, tingling in the lips or tongue, headache, weakness and lack of coordination. The ADA recommends the following treatment for hypoglycemia:
    • Consume 15-20 g of glucose or some simple carbohydrates (examples: 2 tablespoons of raisins; 1Ôüä2 cup of juice or regular soda [not diet]; 1 tablespoon of sugar, honey or corn syrup; or 8 ounces of nonfat or 1% milk).
    • Retest blood glucose after 15 minutes.
    • If hypoglycemia continues, repeat first step.
    • Once blood glucose has returned to normal, eat a small snack if the next planned meal or snack is more than an hour or two away.
  5. What is diabetic ketoacidosis?
    When muscle cells become deficient in glucose uptake, the body burns more fat than usual for energy. This metabolic imbalance produces ketone byproducts from the fat metabolism. When these ketones continually build up, they become toxic acids in the bloodstream. symptoms include those observed with diabetes (Figure2) as well as nausea, vomiting, abdominal pain, difficulty breathing and a fruity odor to the breath (ADA 2014c). The condition is serious and requires medical attention.
  6. What type of diet is best for the prevention and management of diabetes?
    Evidence suggests that a Mediterranean-inspired diet may help prevent type 2 diabetes and improve glucose utilization. This type of diet generally consists of moderate consumption of fish, poultry, vegetables, cereals, fruit, legumes, whole grains, olive oil and wine, and relatively low consumption of red meat (Esposito 2011).
  7. Does yoga help people with type 2 diabetes?
    Yes. Gordon et al. (2008) had 77 adult diabetic subjects (average age 64) complete hathayoga exercise at least 1 day a week for 6 months. Subjects improved their fasting blood glucose and lipid profiles, indicating that hatha yoga may be a safe and viable therapy for type 2 diabetes mellitus. Although these findings are promising, more research is needed in this area.
  8. How should teenagers with type 2 diabetes exercise?
    The ADA (2014d) recommends aerobic exercise, resistance training and recreational activities. With aerobic exercise, start with 10 minutes per day, and progress gradually to 1 hour each day. Resistance training three to four times a week is a target goal. ADA encourages teens to stay active recreationally by dancing, hiking, walking and playing sports with friends and family.
  9. Will eating too much sugar cause diabetes?
    According to the AFA (2014e), evidence suggests that drinking sugary beverages is linked to type 2 diabetes. To prevent the disease, the organization recommends limiting intake of regular soda, fruit punch, fruit drinks, energy drinks, sports drinks, sweet tea and other sugary drinks.
  10. Should people with diabetes avoid starchy foods?
    According to the ADA (2014e), evidence suggests that drinking sugary beverages is linked to type 2 diabetes. To prevent the disease, the organization recommends limiting intake of regular soda, fruit punch, fruit drinks, energy drinks, sports drinks, sweet tea and other sugary drinks.
  11. Resistance Training Recommendations for People With Type 2 Diabetes

    Frequency. At least twice weekly on nonconsecutive days (Colberg et al. 2010); ideally at least three times a week. Colberg and colleagues propose that resistance training should be coordinated with other regular aerobic activities.

    Intensity. For optimal gains in strength and insulin action, resistance training should be performed at moderate intensity (50% of 1-repetition maximum) or vigorous intensity (75%-80% 1-Rm) (Colberg et al. 2010).

    Duration. Five to 10 exercises performed for the major muscles of the upper/lower body and core with at least 10-15 repetitions performed to near fatigue (Colberg et al. 2010). in time, resistance load should increase so the client can attain momentary muscular fatigue with 8-10 reps. a minimum of 1 set to near fatigue is encouraged, but 3-4 sets are recommended for optimal strength gains (Colberg et al. 2010).

    Mode. Resistance machines and/or free weights are appropriate for gains in strength and mass (Colberg et al. 2010). For optimal blood glucose regulation, heavier weights or resistance may be required as strength increases (Colberg et al. 2010).

    Progression. The rate should be slow, to prevent injury. once the target number of repetitions can consistently be exceeded, resistance can begin to increase (Colberg et al. 2010).

    Is High-Intensity Training Appropriate for Type 2 Diabetes?

    Not having enough time for long-duration training sessions prevents a lot of people from sticking with an exercise regimen. in their research review, bird & Hawley (2012) propose that preliminary research indicates that high-intensity interval training is more time efficient than longer-duration aerobic exercise and can produce similar insulin-sensitivity improvements in untrained adults.

    For example, Little et al. (2011) had eight type 2 diabetes subjects (63 ┬▒ 8 years of age) perform six sessions of HIIT training over 2 weeks. The HIIT protocol included 60 seconds of cycling at about 90% of maximal heart rate followed by60 seconds of rest (subjects self-selected to pedal at a very light intensity or to rest passively). Participants completed 10 intervals, and the workout included a 3-minute cycle warm-up and a 2-minute cycle cool-down for a total workout time of25 minutes. Findings showed that this 2-week HIIT program enhanced glucose control and induced skeletal-muscle adaptations that are linked to metabolic-health improvements in patients with type 2 diabetes.

    These encouraging results warrant further long-term research with large-scale clinical trials to determine the most appropriate and effective HIIT training guidelines for type 2 diabetes clients.

    Aerobic Training Recommendations for People With Type 2 Diabetes

    Frequency. At least 3 days a week with no more than 2 consecutive rest days (because of the transient nature of exercise-induced improvements in blood glucose uptake). Colberg et al. (2010) say current guidelines recommend five sessions of moderate activity per week.

    Intensity. At least moderate, approximately 40%-60% of maximal aerobic capacity (Colberg et al. 2010). Brisk walking and other “somewhat hard” exercises usually qualify as moderately intense for most people with type 2 diabetes (Colberg et al. 2010). Gradual increases in intensity yield more health benefits. Training intensity is a better predictor of improved blood glucose control than training volume, so clients should increase intensity before increasing volume (Colberg et al. 2010).

    Duration. At least 150 minutes per week at moderate intensity or higher. Aerobic activities should last at least 10 minutes and be spread throughout the week. Around 150 minutes per week of moderate-intensity exercise is associated with reduced morbidity and mortality in all populations, though further benefits are likely for those who go beyond the recommended durations (Colberg et al. 2010).

    Mode. Aerobic exercises that innervate large muscle groups and cause sustained increases in heart rate are likely to be beneficial. engagement in a variety of aerobic exercise modes should be encouraged.


References

ADA (American Diabetes Association). 2013. American Diabetes Association fast facts. http://professional.diabetes.org; accessed June 7, 2014.

ADA. 2014a. Standards of medical care in diabetes—2014. Diabetes Care, 37 (Suppl. 1), S14-S80.

ADA. 2014b. Hypoglycemia (low blood glucose). www.diabetes.org/living-with-diabetes/treatment-and-care/blood-glucose-control/hypoglycemia-low-blook.html; accessed June 7, 2014.

ADA. 2014c. DKA (ketoacidosis) & ketones. www.diabetes.org/living-with-diabetes/complications/detoacidosis-dka.html?loc=lwd-slabnav; accessed June 6, 2014.

ADA. 2014d. Children and type 2 diabetes. www.diabetes.org/living-with-diabetes/parents-and-kids/children-and-type-2; accessed June 6, 2014.

ADA. 2014e. Diabetes myths. www.diatetes.org/diabetes-basics/myths/; accessed June 6, 2014. ADA 2014f. Diagnosing diabetes and learning about prediabetes. www.diabetes.org/diabetes-basics/diagnosis; accessed June 6, 2014.

Bird, S.R., & Hawley, J.A. 2012. Exercise and type 2 diabetes: New prescription for an old problem. Maturitas, 72 (4), 311-16.

CDC (Centers for Disease Control and Prevention). 2014. National Diabetes Statistics Report, 2014. www.cdc.gov/diabetes/pubs/statsreport14.htm; accessed July 8, 2014.

Colberg, S.R., et al. 2010. Exercise and type 2 diabetes. Diabetes Care, 33 (12), e147-67.

Esposito, K., et al. 2011. Prevention and control of type 2 diabetes by Mediterranean diet: A systematic review. Diabetes Voice, 56 (1), 29-31.

Gordon, L.A., et al. 2008. Effect of exercise therapy on lipid profile and oxidative stress indicators in patients with type 2 diabetes. BMC Complementary and Alternative Medicine, 8 (21). doi:10.1186/1472-6882-8-21.

IDF (International Diabetes Federation). 2014. Types of diabetes. www.idf.org/types-diabetes; accessed June 7, 2014.

Little, J.P., et al. 2011. Low-volume high-intensity interval training reduces hyperglycemia and increases muscle mitochondrial capacity in patients with type 2 diabetes. Journal of Applied Physiology, 111 (6), 1554-60.

Ploug, T., & Ralston, E. 2002. Exploring the whereabouts of GLUT4 in skeletal muscle(review). Molecular Membrane Biology, 19 (1), 39-49.
Ruder, K. 2011. American Diabetes Association Complete Guide to Diabetes. Alexandria, VA: American Diabetes Association.
Zajac, J., et al. 2010. The main events in the history of diabetes mellitus. In Leonid Poretsky (Ed.), Principles of Diabetes Mellitus (2nd ed., pp. 3-16). New York: Springer.

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