Resistance Training for Clients with Diabetes
Len Kravitz, Ph.D.
Article Reviewed: Irvine, C. and Taylor, N.F. (2009). Progressive resistance exercise improves glycaemic control in people with type 2 diabetes mellitus: a systematic review. Australian Journal of Physiotherapy, 55, 237-246.
Diabetes is a metabolic disorder resulting in individuals having elevated blood plasma glucose levels which may lead to numerous health maladies including neuropathy (disease affecting nerves), retinopathy (disease of retina), nephropathy (kidney disease) and increased risk to cardiovascular disease (Irvine and Taylor, 2009). Obesity and a lack of physical activity are major risk factors for the development of type 2 diabetes. The centerpieces of diabetes management are exercise, nutrition and oral medications. Traditionally, the exercise intervention for persons with diabetes has been cardiovascular exercise, due to its positive effect in helping to normalize the disordered glycemic (i.e., sugar in the blood) control in the body (Gulve, 2008). However, within the last decade the glucose (Greek word for sweet) lowering effects of resistance training have been documented. The results of this research and subsequent practical applications will be the topic of this research column.
How Does The Body Regulate Glucose?
The primary organs that regulate blood glucose are skeletal muscle, the liver and pancreas. Skeletal muscle is a major organ consumer of glucose for energy to power the force production needs of the muscle. The liver is the chief organ that stores glucose after food ingestion and distributes it into the circulation between meals for proper levels in the blood. Insulin is released from pancreas beta cells in response to the ingestion of food. Insulin then stimulates the uptake and storage of glucose in skeletal muscle (stored as glycogen for fuel) and the liver (stored as glycogen for fuel) and in adipose tissue (used to synthesize triglycerides).
Does Resistance Training Improve Glycemic Control? The Study Methods
Irvine and Taylor (2009) completed a review of 9 randomized control-group studies (352 adults; 232 men and 120 women with type 2 diabetes for 5-9 years; average age = 58 years), which met rigorous scientific criteria for inclusion (449 studies originally evaluated). All studies were 8 or more weeks in length and followed resistance training guidelines established by the American College of Sports Medicine (resistance exercise 2-3 times a week; 1-3 sets of 8-12 repetitions progressing from a load of 45/50% to 70/80% of the 1-repeition maximum). Eight of the nine studies met 3 times a week for resistance training while one study met two times a week. The resistance training interventions lasted 8 to 26 weeks (average was 20 weeks) with each workout session lasting 45-50 minutes. Most of the studies had subjects completed 2-3 sets of 8-15 repetitions on 5-10 exercises (major muscle groups). All studies had subjects progressively increase the resistance training intensity throughout the study duration.
The primary outcome measure to determine if resistance training was effective for improving glycemic control was measured by percentage of glycosylated hemoglobin (HbA1c). HbA1c is a form of hemoglobin that is used to identify the average blood glucose concentration over a prolonged period of several months (Mathur, 2009).
Does Resistance Training Improve Glycemic Control? The Study Results
When compared with non-exercise controls in 7 studies, the progressive resistance training lowered HbA1c by a small (0.3%) but significant amount. The studies with aerobic training groups showed similar changes in HbA1c. Irvine and Taylor (2009) summarize that a 1% decrease in HbA1c is associated with a 37% decrease in the risk of microvascular complications and a 21% decrease in the risk of death associated with diabetes. Comparatively, oral hypoglycemic medications can reduce HbA1c by 0.5 to 2%. The authors note that the medications are costly and often have adverse gastrointestinal side effects. Dietary interventions, such as individualized meal plans, tend to lower HbA1c about 0.43 to 1% in those with established diabetes (Irvine and Taylor). Secondary measurements of muscle strength in all studies also showed significant changes in improvement.
Practical Recommendations to Exercise Professionals
Irvine and Taylor (2009) summarize that the lowered HbA1c values from progressive resistance training program is very positive. The authors advocate that resistance training should not be considered a 'stand alone' intervention for men and women with diabetes (due to the contributing importance of diet and other lifestyle changes). However, exercise professionals now have solid evidence-based research that resistance training will not only help to prevent diabetes (for those who do not have it), but also help to manage diabetes for clients who have this metabolic disorder. Successful resistance training programs followed a progressive resistance training program (45/50% to 70/80% of the 1-repeition maximum; 1-3 sets per exercise) focusing on the major muscles of the body (e.g., gluteals, thighs, chest, back, core, shoulders and arms), and met for the most part for 3 times a week. For some personal trainers training diabetes clients with multiple morbidities (e.g., cardiovascular disease, osteoporosis, and peripheral vascular disease), aerobic exercise participation may be very limited. With these clients, progressive resistance training may serve as the primary exercise intervention. For clients capable of performing aerobic exercise, Sigal et al. (2007) compared aerobic exercise (15 minutes progressing to 45 minutes on 3 days per week), resistance exercise (1-3 sets on 7 different exercises of the major muscle groups) and combined (aerobic and resistance exercise) with 251 adults (39-70 years) for 22 weeks and concluded that glycemic control improvements (as measured by HbA1c) are greatest with the combined aerobic exercise and resistance training program. Be proactive with your clients! Exercise is a confirmed intervention that makes an impressive health difference with clients who have diabetes, and may help prevent it for those who do not.
Side Bar 1: Important Questions About Diabetes
1) Since high blood glucose is dangerous, is low blood glucose healthy? When blood glucose levels fall below 70 mg/dl, it is called hypoglycemia or low blood glucose. Since the primary fuel of the central nervous system (CNS) is glucose, low blood glucose can dramatically impair CNS function. Hypoglycemia can lead to dizziness, confusion, slurred speech, blurred vision and sleepiness (Gulve, 2008).
2) What is glycosylated hemoglobin and the HbA1c test? Glycosylation is the process of adding sugar units to a molecule, When glucose links or sticks with the hemoglobin of red blood cells (called glycosylated hemoglobin) it may impair the function of other molecules in nerve cells, retina cells and blood vessels. As sugar sticks to these cells, it indicates how much sugar has been around for the preceding three months, as red blood cells live for about this long. This is what the HbA1c measurement assesses. The normal range of HbA1c is 4-5.9%, while in poorly controlled diabetes it is at 8.0% or above, and about 7.0% in persons with well-controlled diabetes (Mathur, 2009). The benefit of measuring HbA1c in studies and clinical medicine is that is gives a more realistic view of what's happening over the course of several months.
3) What are the risk factors for diabetes? According to the American Heart Association (2008), the risk factors for diabetes are family history, race (Asian, Hispanic, Native American, and African have higher risk), overweight/obesity, age (the older a person the higher the risk), hypertension, heavy alcohol consumption over time, cigarette smoking, and a history of gestational diabetes (developing diabetes during pregnancy or delivering a baby over 9 lbs). It is consequential to note that moderate alcohol consumption (1 drink/day for women and 2 drinks/day for men) may lower the risk of diabetes (Collazo-Clavell, 2009).
4) Will eating too many simple sugars cause diabetes? Not directly. Type 1 diabetes is a genetic disorder in which the body is unable to produce insulin. Type 2 diabetes is highly affected by lifestyle factors (see above) and a history of diabetes in your family. Eating too many sugars may lead to overweight and obesity, which then will become a risk factor for type 2 diabetes.
5) So, can people with diabetes eat sweets and chocolates? Yes, if eaten as part of a healthy meal plan and combined with exercise (American Diabetes Association, 2010). The American Diabetes Association encourages people with diabetes to eat a healthy diet that is high in whole grain foods, fruits, and vegetables but low in trans fat and saturated fat. The organization suggests moderation in sugar and salt intake.
6) Please explain what insulin resistance and glucose intolerance mean? Insulin resistance occurs when the body fails to respond properly to the insulin it already produces. This may lead to a condition referred to as glucose intolerance where the body has blood sugar levels higher than normal (in the pre-diabetes range; see Figure 1), but not high enough to classify as diabetes.
Additional References:
American Diabetes Association. (2010). Type 1
http://www.diabetes.org/diabetes-basics/type-1/ Retrieved March 23, 2010
American Heart Association. (2008). Prediabetes
http://www.americanheart.org/presenter.jhtml?identifier=3044760#what_does Retrieved March 23, 2010.
Collazo-Clavell, M. (2009). Does alcohol and tobacco use increase the risk of diabetes?
http://www.mayoclinic.com/health/diabetes/AN00548 Retrieved March 23, 2010.
Gulve, E.A. Exercise and glycemic control of diabetes: benefits, challenges, and adjustments to pharmacotherapy. Physical Therapy, 2008, 88, 1297-1321.
Mathur, R. Hemoglobin A1c Test. (2009). Hemoglobin A1c Test http://www.medicinenet.com/hemoglobin_a1c_test/article.htm Retrieved March 23, 2010.
Sigal R.J., Kenny G.P., Boulé N.G., Wells G.A. et al. (2007). Effects of aerobic training, resistance training, or both on glycemic control in type 2 diabetes: a randomized trial. Annals of Internal Medicine, 147(6):357-69.
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