{mosimage}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
1. 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.
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Clinical Context
The 1995 Centers for Disease Control and American College of Sports Medicine position statement recommends 30 minutes of moderate intensity activity on most, if not all, days of the week in all adults. However, there is currently controversy as to whether 30 or 60 minutes per day of exercise should be the national recommendation, although experts agree that inactivity is detrimental to health, some exercise is better than none at all, and more exercise leads to better health benefits. The metabolic syndrome is defined with use of revised ATP III criteria as meeting 3 or more of the following criteria: increased waist circumference of 102 cm or more in men and 88 cm or more in women, increased triglyceride levels of 150 mg/dL or higher, decreased HDL cholesterol levels of 40 mg/dL or less in men and 45 mg/dL or less in women, increased blood pressure (BP) of 130 mm Hg systolic or higher or 85 mm Hg diastolic or higher, and increased fasting blood glucose level of 100 mg/dL or higher.
This is a 6-month randomized controlled trial of overweight and obese men and women in the STRRIDE study to examine the effect of various predefined intensity and durations of exercise on risk factors for the metabolic syndrome in men and women.
Study Highlights
- Included were 334 subjects who were overweight or mildly obese (BMI, 25 – 35 kg/m2), sedentary, and aged 40 to 65 years with no history of cardiovascular disease, diabetes, or hypertension.
- All women were postmenopausal.
- Inclusion criteria included increased low-density lipoprotein cholesterol (130 – 190 mg/dL) or decreased HDL cholesterol levels (< 40 mg/dL for women and < 45 mg/dL for men).
- Excluded were those who smoked or used lipid-lowering drugs.
- 334 subjects were randomized to 1 of 4 groups; of 227 who completed the study, 171 had complete data for all 5 criteria for the metabolic syndrome and were included in the analysis.
- 1 control group was assigned to no exercise, and 3 exercise groups were assigned as follows: low-amount/moderate-intensity group equal to 19 km or 12 miles a week at 40% to 55% peak oxygen consumption, low-amount/vigorous-intensity group, and high-amount/vigorous-intensity group at 65% to 80% peak oxygen consumption.
- Energy expenditure was 14 kcal/kg for the 2 low-amount groups and 23 kcal/kg for the high-amount group.
- Adherence was calculated for each exercise group as minutes at assigned heart rate per week divided by minutes prescribed.
- Intensity of exercise was based on maximal cardiopulmonary exercise, and all groups had 2 to 3 months of gradual increase in exercise intensity to minimize injury, followed by 6 months of training at the assigned exercise prescription.
- All exercise sessions were verified by direct supervision or heart rate monitors that supplied recorded heart rate files.
- The control group was instructed to maintain an inactive lifestyle for 6 months.
- All groups maintained their usual diet.
- At baseline anthropometric measurements, BP, lipid levels, and insulin sensitivity were measured.
- A z score was used as a continuous score for the 5 variables of the metabolic syndrome.
- Sex-specific z scores were used to account for variations in ATP III criteria for men and women.
- Main outcomes were improvement in z score and number of risk factors at the end of 6 months.
- Mean age at baseline was 53 years, half were men, mean BMI was 30 kg/m2, mean systolic BP was 130 mm Hg, and mean diastolic BP was 84 mm Hg.
- Mean fasting blood glucose level was 95 mg/dL at baseline.
- At baseline, women showed more desirable risk profile than men.
- 40% of 171 subjects had 3 or more criteria for the metabolic syndrome (46% men and 34% women).
- Both low-amount/moderate-intensity and high-amount/vigorous-intensity groups had significantly decreased ATP III z scores vs controls.
- There was evidence that moderate-intensity was better than vigorous-intensity exercise in improving z score.
- The high-amount/vigorous-intensity group had the highest number of improved risk factors for the metabolic syndrome.
- Waist circumference significantly improved for all 3 exercise groups.
- Triglyceride levels were significantly lower in the low-amount/moderate-intensity but not in the low-amount/vigorous-intensity group.
- In men, z score decreased significantly for both the moderate- and vigorous-intensity groups.
- Women in the high-amount/vigorous-intensity group had a significant decrease in z score.
- In all 3 exercise groups, the number of subjects with ATP III–defined criteria for the metabolic syndrome decreased, whereas in the control group the number of subjects with such criteria increased in 6 months.
- There was a significant decrease in the prevalence of the metabolic syndrome and numbers of subjects who met criteria for waist circumference, triglyceride levels, and BP in the exercise groups in 6 months.
Pearls for Practice
- In middle-aged overweight and obese men and women, moderate- and vigorous-intensity exercise, even modest amounts equivalent to walking 17 km for an average of 170 minutes per week during 6 months, is associated with significant improvement in risk factors for the metabolic syndrome.
- The benefit of exercise for the metabolic syndrome is dose dependent, with greater improvement with higher amounts of exercise.
