Irvine, C., & 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, 237–46.
Diabetes is a metabolic disorder resulting in elevated blood plasma glucose levels. It can lead to numerous health maladies, including neuropathy (disease affecting nerves), retinopathy (disease of retina), nephropathy (kidney disease) and increased risk for cardiovascular disease (Irvine & Taylor 2009). Obesity and 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, owing 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-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.
The Body’s Regulation of Glucose
The primary organs that regulate blood glucose (glucose is Greek for “sweet”) are skeletal muscle, the liver and the 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 the glucose into circulation between meals to maintain proper blood sugar levels. Insulin is released from pancreatic 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).
Resistance Training and Glycemic Control
The Study Methods. Irving and Taylor completed a review of nine randomized controlled studies that met rigorous scientific criteria for inclusion (449 studies were originally evaluated). Study subjects were 232 men and 120 women (average age 58 years) who had lived with type 2 diabetes for 5–9 years. All studies followed resistance training guidelines established by the American College of Sports Medicine (i.e., 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 1-repetition maximum (1-RM). In eight of the nine studies, participants met 3 days a week for resistance training, while in one study they met twice a week. The resistance training interventions lasted 8–26 weeks (average was 20 weeks), with each workout session lasting 45–50 minutes. Most studies had subjects completing 2–3 sets of 8–15 repetitions on five to 10 exercises (major muscle groups). All studies had subjects progressively increasing the resistance training intensity throughout the study duration.
The primary outcome measure to determine if resistance training was effective for improving glycemic control was percentage of glycosylated hemoglobin (HbA1c). HbA1c is a form of hemoglobin used to identify the average blood glucose concentration over a prolonged period of several months (Mathur 2009). (See the sidebar “Important Questions About Diabetes” for more about HbA1c, and see Figure 1 for an explanation of laboratory tests for prediabetes and diabetes).
The Study Results. Compared with nonexercise controls in seven studies, the progressive resistance training lowered HbA1c in study participants by a small (0.3%) but significant amount. The studies with aerobic training groups showed similar changes in HbA1c. Irving and Taylor 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%–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%–1% in those with established diabetes. Secondary measurements of muscle strength in all studies also showed significant improvement.
Irving and Taylor summarize that the lowered HbA1c values from a progressive resistance training program are very positive. The authors advocate that resistance training should not be considered a “stand-alone” intervention for men and women with diabetes, given the contributing importance of diet and other lifestyle changes. However, exercise professionals now have solid research-based evidence that resistance training not only helps to prevent diabetes for those who do not have it, but also helps to manage diabetes for clients who have this metabolic disorder.
Successful resistance training programs followed a progressive resistance training regimen (45%–50% to 70%–80% of 1-RM; 1–3 sets per exercise) focusing on the major muscles of the body (e.g., gluteals, thighs, chest, back, core, shoulders and arms). For the most part, they met 3 days a week. For some personal trainers working with 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 3 days per week), resistance exercise (1–3 sets of seven different major muscle exercises) and combined (aerobic and resistance exercise) with 251 adults (39–70 years) for 22 weeks. They 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.