With commentary by Michael Trenell, PhD, researcher, Newcastle University, Newcastle upon Tyne, UK.
In the study, Professor Michael Trenell and his team from Newcastle University in the U.K. randomly assigned 23 men and women, ages 45 to 71, all with type 2 diabetes, to one of two groups. One group engaged in 12 weeks of intense but brief bursts of exercise. The others did not and served as the comparison or control group.
In the high-intensity group, the men and women rode an indoor cycle three times a week. They gradually increased their pedaling from very light to very hard, putting in five brief intervals of high-intensity pedaling. The high-intensity bouts lasted just two minutes at first and up to nearly four minutes by the final week.
The high-intensity, short bursts improved how the heart works, Trenell says. Experts know that those with type 2 diabetes often have early changes in the structure and function of the heart, affecting the left ventricle, which receives blood from the left atrium and pumps it out to the body.
Trenell found that the high-intensity bursts of exercise improved the ability of the left ventricle to take in blood by 24 percent and made it more efficient. "This means that for every heart beat, the heart is able to not only pump more blood around the body, but it also does this in a more efficient way," Trenell says.
As for why it works, he says that ''raising your heart rate helps make the heart adapt by becoming larger and working more efficiently."
Currently, exercise guidelines suggest less intensity and longer durations, he says. However, "higher intensities of exercise for shorter duration but repeated are, for some people, easier to do than longer bouts of exercise at a lower level," he says. Trenell and other experts say that adherence to the advice to exercise is not heeded by many with diabetes.
Trenell also found modest improvements in blood sugar control in the high-intensity exercisers. On average, these exercisers saw a .3 percent reduction in A1C, a measure of blood sugar control over the past two to three months. The improvement was only modest, he says. "However, the changes in the heart were pronounced, highlighting the importance of exercise beyond diabetes control alone," he says.
The high-intensity, short bursts of exercise reduced liver fat by 39 percent, the researchers also found. And that can translate to better blood sugar control, Trenell says. "Excess fat in the liver plays a critical role in blood sugar control, affecting both fasting and post-prandial [meal] glycemia," he says. "Our data highlights the important of liver fat, as the greater the reduction in liver fat, the greater the improvement in diabetes control."
The study is published in the journal Diabetologia.
The study findings are important, says Om Ganda, MD, director of the Lipid Clinic at Joslin Diabetes Center, Boston, noting that ''patients with type 2 diabetes have two times the incidence of heart failure, compared to the healthy population."
He reviewed the findings. Among the study limitations, however, is the relatively short duration of the study, just 12 weeks, he says. Those in the study already had relatively well controlled blood sugar levels, he says, with A1C averaging about 7 percent. An A1C of 7 percent is a common treatment target, according to the American Diabetes Association. It would be important to know how well the exercise plan works in those with poor blood sugar control, Ganda adds.
Even so, he says, "this study adds to the evidence that intensity and duration of exercise has additional cardiovascular benefits." The Joslin clinical guidelines currently say that "a target of 60-90 minutes, 6-7 days per week is encouraged for weight loss in overweight or obese people with diabetes." Other guidelines suggest exercising 30 minutes, five days a week, moderately, Dr. Ganda says. "Unfortunately, most patients are relatively sedentary and the adherence to recommendations is poor," he says. Even so, more study is needed about the high-intensity exercise before any firm recommendations can be made, he says.