Walk, Don't Run, to Prevent or Reverse Metabolic Syndrome

Michael O'Riordan
December 19, 2007 — For overweight or obese individuals who are physically inactive, brisk walking might be the best exercise prescription for shedding excess pounds and reducing the risk of metabolic syndrome. Data from a new analysis showed that in a middle-aged at-risk physically inactive population, moderate-intensity exercise in the absence of dietary changes significantly reduced the prevalence of metabolic syndrome.
"These results give a lot of credence to the fact that individuals don't necessarily have to go out and do a lot of intensive exercise to receive health benefits," senior investigator Dr William Kraus (Duke University Medical Center, Durham, NC) told heartwire.
The post hoc analysis of the National Institutes of Health-funded Studies of a Targeted Risk Reduction Intervention through Defined Exercise (STRRIDE) trial is now published in the December 15, 2007 issue of the American Journal of Cardiology.
Any exercise better than none, but intense not necessarily better
Speaking with heartwire, Kraus said the purpose of the study was to identify the effects of different exercise programs on the metabolic syndrome. Previous exercise studies have looked at the effects of exercise on various components of the syndrome — increased waist circumference, low high-density lipoprotein (HDL) cholesterol, increased triglyceride levels, hypertension, and impaired fasting glucose — but very few studies have examined how exercise affects the metabolic syndrome as a whole.
In this analysis, the investigators analyzed data from 171 men and women with complete pre- and posttraining data for all five metabolic syndrome criteria. All subjects were overweight to mildly obese sedentary adults — body mass index (BMI) 25 to 35 kg/m2 — with no known history of cardiovascular disease, diabetes, or hypertension.
Subjects were assigned to one of three exercise programs, each eight months in duration:
Low-amount/moderate-intensity exercise: approximately 12 miles/week at 40% to 55% peak oxygen consumption.
Low-amount/vigorous-intensity exercise: approximately 12 miles/week at 65% to 80% peak oxygen consumption.
High-amount/vigorous-intensity exercise: approximately 20 miles/week at 65% to 80% peak oxygen consumption.
Prior to beginning the exercise program, 40% of subjects met three of more of the criteria for metabolic syndrome. By the completion of the trial, 27% of the participants met the National Cholesterol Education Program (NCEP) Adult Treatment Panel (ATP) III criteria for the metabolic disorder.
Investigators also found that the low-amount/moderate-intensity exercise program reduced the prevalence of the metabolic syndrome relative to inactive controls, but this same amount of exercise at vigorous intensity was not significantly better than the inactive control group. Those who participated in high-amount/vigorous-intensity exercise improved the metabolic syndrome relative to controls as well as to the low-amount participants, all suggesting an exercise dose effect, say investigators.
These findings show that "inactivity is bad for you, and that anything is better than doing nothing, but more is not necessarily better than less," said Kraus. The findings supporting moderate-intensity exercise such as walking 30 minutes per day six days per week, added Krauss, are consistent with the American College of Sports Medicine/Centers for Disease Control exercise recommendations for health effects.
Asked about the possible reason those who participated in the low-amount/high-intensity exercise program did not improve as much as those who performed less intensive exercise, Kraus suggests that rigorous exercise recruits more fast-twitch muscle fibers and utilizes glucose to a much greater extent than low-intensity exercise. Low-intensity exercise, on the other hand, tends to recruit slow-twitch fibers and uses free fatty acids as a substrate for energy. This, he said, is more beneficial for preventing or reversing the metabolic syndrome.
Source
Johnson JL, Slentz CA, Houmard JA, et al. Exercise training amount and intensity on metabolic syndrome (from Studies of a Targeted Risk Reduction Intervention through Defined Exercise). Am J Cardiol 2007; 100:1759-1766.