Exercise and Metabolic Syndrome: Review
Pub Date: Thursday, August 21, 2008
Author: Roger S. Blumenthal, MD
From 2004-2005, researchers in Norway performed a study looking at the effect that different types of exercise programs had on people diagnosed with metabolic syndrome. Metabolic syndrome is diagnosed when a person has more than 3 of the following criteria: abdominal obesity (waist circumference >40 or >35 inches for men and women, respectively), high fasting-triglyceride level (>150 mg/dL) or taking triglyceride-lowering medication, low high-density lipoprotein cholesterol (HDL-C) level (<40 mg/dL in men or <50 mg/dL in women), blood pressure >130/85 mm Hg or taking medication to lower blood pressure, and fasting glucose level >100 mg/dL or taking diabetes medication to lower blood glucose.
Currently, more than 300 million people have metabolic syndrome worldwide with an estimated 25% of American adults being affected. People with metabolic syndrome are approximately two to three times more likely to die from coronary heart disease than those without metabolic syndrome. Along with the rise of obesity, the incidence of metabolic syndrome is expected to increase in the coming years. The good news, however, is that regular physical activity has been shown to reverse the metabolic syndrome, allowing those people diagnosed with it to greatly decrease their risk of having or dying from a heart attack.
This study looked at two different exercise programs to determine which was most effective at reversing the metabolic syndrome. Thirty-two people diagnosed with the metabolic syndrome were divided into three groups: (1) aerobic interval training (AIT), (2) continuous moderate exercise (CME), or (3) a control group.
The AIT program had people warm up at 70% of their maximum heart rate (determined by subtracting their age from 220 beats per minute) for 10 minutes followed by four 4-minute intervals of intense exercise (90% of their maximum heart rate) with 3-minute recovery periods at 70% of their maximum heart rate between these intense intervals. The program ended with a 5-minute cool-down period. The CME program had people perform a 47-minute session at 70% of their maximum heart rate. Both exercise programs occurred three times a week for 16 weeks.
Both before and after the 16-week exercise program, the researchers performed many tests and measurements in order to see exactly what effect the two workout routines had on the participants in the study. The researchers found that participants in both the AIT and CME groups had slightly lower weights (3% and 4%, respectively) as well as lower body mass index (BMI) and waist width, all important factors in diagnosing the metabolic syndrome.
Blood pressure, another component of the metabolic syndrome, was lowered in both the AIT and CME groups. Systolic blood pressure was lowered by about 10 mm Hg, while diastolic blood pressure was lowered by about 6 mm Hg in both groups. While it may seem like a relatively small change, in observational studies this decrease in blood pressure is associated with a 30%-40% decrease in the risk of premature death due to stroke or ischemic heart disease.
Despite having similar effects on body weight and blood pressure, the AIT group showed more improvement in insulin sensitivity and aerobic capacity, as well as HDL-C levels. Insulin resistance, leading to high blood-glucose levels, is one of the five conditions comprised in the metabolic syndrome. Participants from the AIT group had higher insulin sensitivity, as well as lower blood-glucose levels than participants from the CME or control groups.
Of all the risk factors for heart disease, low aerobic-exercise capacity has been shown to be the strongest predictor of mortality. Participants in the AIT group increased their maximal oxygen uptake by 35% over the 16-week program, while the CME group increased their maximal oxygen uptake by just 16%. The AIT group was probably able to increase their maximal oxygen uptake by a greater margin because the pumping capacity of the heart limits the maximal oxygen uptake; performing short work periods at high intensities challenges the heart's pumping ability more than just performing at a constant lower intensity.
The AIT program also showed benefits not directly related to the metabolic syndrome. Participants from the AIT program had an increase of 25% in HDL-C levels, while participants from the CME and control groups showed no change in HDL-C levels. Also, participants noted that the AIT program's varying procedure kept them more interested and motivated, while the CME program's constant walking was perhaps not as interesting. Thus, besides being more beneficial, the AIT program may be easier for the average person to complete on a regular basis.
This study showed that the intensity of exercise was an important factor for reversing factors of the metabolic syndrome as well as increasing aerobic capacity. More specifically, high-intensity training, such as the AIT program, is more beneficial in preventing and reversing metabolic syndrome compared to constant, moderate-intensity programs (like CME). With the incidence of metabolic syndrome expected to increase in the future, this study provides important information about what people can do to prevent or reverse the metabolic syndrome and, thus, decrease their risk for having and dying from a heart attack.
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The opinions expressed in this commentary are not necessarily those of the editors or of the American Heart Association