News & Research

Abnormal skeletal muscle recruitment during exercise in patients with type 2 diabetes mellitus and microvascular complications, by Lisa Womack and colleagues. Journal of the American College of Cardiology 53:2175–2183, 2009

What is the problem and what is known about it so far?

In healthy individuals without diabetes, high insulin levels that may occur, for example, after a carbohydrate-rich meal, trigger tiny blood vessels in muscles to take in more blood and thus more quickly process glucose from the bloodstream. Exercise has the same stimulating effect on blood vessels in the muscle, resulting in more rapid blood flow. In people with type 2 diabetes who are insulin resistant (whose bodies do not respond appropriately to insulin) this triggering of muscle blood vessels is impaired. This may contribute to high blood glucose levels and the development of diabetes complications. It is not known whether the similar triggering of muscle blood vessels by exercise is also impaired in people with diabetes.

Why did the researchers do this particular study?

The researchers wanted to find out whether exercise properly triggers muscle blood vessels in people with type 2 diabetes.

Who was studied?

The study included 20 healthy control subjects, 22 patients with diabetes, and 8 patients with both diabetes and microvascular (small blood vessel) complications of diabetes.

How was the study done?

With participants fasting, researchers used high-tech imaging devices to measure blood flow and blood volume in participants’ forearms at rest and while during low- and high-intensity handgrip exercises.

What did the researchers find?

Muscle blood vessels responded to exercise similarly in those with and without diabetes, but responses were reduced in those with diabetic blood vessel complications.

What were the limitations of the study?

The small number of subjects in this study did not allow researchers to perform statistical tests to rule out other factors that may have affected muscle blood vessel performance. Also, this study was performed only in fasting participants, while other studies have reported similar results in nonfasting participants as well. Finally, researchers did not estimate the size of participants’ forearm muscles, which could have influenced blood-flow responses.

What are the implications of the study?

Exercise seems to trigger muscles to take in blood and process glucose appropriately in uncomplicated type 2 diabetes, but this triggering mechanism is hindered in people with diabetic blood vessel complications. Larger studies are needed to learn more about the causes of this problem.

FOR MORE INFORMATION

Insulin resistance

Diabetes complications

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