Interval training may be the best type of exercise to affect metabolic syndrome

Excessive caloric intake, increased refined carbohydrate consumption and lack of regular, sustained, brisk physical activity have led to a steady increase in the incidence of abdominal obesity and an emerging epidemic of insulin resistance.

Abdominal obesity has tripled in the United States during the last four decades, currently affecting about half of all adults. Along with the rise in obesity, the incidence of metabolic syndrome is expected to increase in the coming years and people with metabolic syndrome are more likely to die from coronary heart disease than those people without it.

Exercise can help

The good news, however, is that exercise has been shown to reverse metabolic syndrome, allowing those people diagnosed with this disorder to decrease their risk for having or dying from an MI.

In a 2002 study, researchers followed more than 3,200 people with elevated glucose levels. They found that lifestyle changes, which included exercise and weight loss, reduced the progression to type 2 diabetes by >50% vs. those who did not partake in the diet and exercise program. Moreover, the diet and exercise program was even more effective than taking medication alone, showing the importance of exercise for those people with metabolic syndrome.

Currently, experts recommend more than 30 minutes of moderate, brisk exercise about five times a week. These 30 minute sessions can be done all at once, or they can be done in many short bursts, such as walking up the stairs instead of taking the elevator. Moderate exercise involves increasing one’s heart rate to 50% to 70% of its maximum level or walking at about three miles per hour. (An easier way to determine moderate exercise levels is to make sure you can still have a conversation while exercising.)

A short warm-up period before exercising and a five minute cool down period after exercising are advised to limit any danger associated with rapidly increasing or decreasing one’s heart rate. If at any time during exercise people experience any symptoms such as pain or pressure in the chest, arms, neck, or jaw, dizziness, nausea, shortness of breath, or rapid heartbeat, they should stop immediately and contact a doctor.

Interval vs. continuous exercise

From 2004 to 2005, researchers in Norway performed a study to look at the effect that different types of exercise programs had on people diagnosed with metabolic syndrome. They looked at two different exercise programs in an attempt to identify which is most effective at reversing metabolic syndrome. Thirty-two people diagnosed with metabolic syndrome were divided into three groups; aerobic interval training, continuous moderate exercise or a control group.

The aerobic interval training 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 three minute recovery periods at 70% of their maximum heart rate between these intense intervals. The program ended with a five minute cool-down period.

Participants performed the continuous moderate exercise program a session about 45 minutes at 70% of their maximum heart rate. Both exercise programs were designed to expend equal amount of calories per workout section and occurred three times a week for 16 weeks.

The researchers performed tests and measurements throughout the study to evaluate the effect of the two different exercise routines on the criteria for the diagnosis of metabolic syndrome and other markers of cardiovascular health. Slightly lower weights were observed in the aerobic interval training group (3%) and the continuous moderate exercise group (4%), as well as lower BMI and waist circumference, all important components of metabolic syndrome.

BP was lowered in both the aerobic interval training and continuous moderate exercise groups. Systolic BP was lowered by about 10 mmHg, and diastolic BP was lowered by about 6 mmHg in both groups. Although it may seem like a relatively small change, in observational studies this decrease in BP is associated with a 30% to 40% decrease in the risk for premature death due to stroke or ischemic heart disease.

Despite having similar effects on body weight and BP, the aerobic interval training group showed more improvement in insulin sensitivity, aerobic capacity and HDL levels. Along with higher insulin sensitivity, participants from the aerobic interval training group had lower blood glucose levels than participants from the continuous moderate exercise or control groups.

Of all the risk factors for heart disease, low aerobic exercise capacity has been shown to be the strongest predictor of death. Participants in the aerobic interval training group increased their maximal oxygen uptake by 35% during the 16-week program, whereas the continuous moderate exercise group increased their maximal oxygen uptake by 16%. The aerobic interval training group probably was able to increase their maximal oxygen uptake by a greater margin because performing short work periods at high intensities challenges the heart’s pumping ability more than just performing at a constant, lower intensity.

Participants in the aerobic interval training program had an increase of 25% in HDL levels, whereas participants from the continuous moderate exercise and control groups showed no change in HDL levels. Also, participants noted that the aerobic interval training program’s varying procedure kept them more interested and motivated, whereas the continuous moderate exercise program’s constant walking was perhaps not as interesting. Thus besides being more beneficial, the aerobic interval training program may be more appealing for the average person to complete on a regular basis.

Overall, the findings from this study confirmed the findings from prior studies that showed the importance of exercise, in any form, in reducing cardiovascular risk. Additionally, the findings from this study were the first to show that the intensity of exercise can be an important factor for reversing factors of metabolic syndrome and improving other measures of cardiovascular health, including aerobic capacity. These findings suggest that high-intensity interval exercise training is more beneficial to preventing and reversing metabolic syndrome compared with constant, moderate-intensity programs.

With the incidence of metabolic syndrome expected to increase in the future, the researchers provided important information about the most effective type of exercise training to prevent cardiovascular events in individuals with metabolic syndrome.

Before beginning any new exercise program, people who already have or are at high risk for developing CHD should consult their doctor to create a safe and effective plan.

George Clements is a premedical student at The Johns Hopkins Ciccarone Center for the Prevention of Heart Disease.

Andrew DeFilippis, MD, MSc, is a Cardiology Fellow at The Johns Hopkins Ciccarone Center for the Prevention of Heart Disease.

Roger S. Blumenthal, MD, is a Professor of Medicine and Director at The Johns Hopkins Ciccarone Center for the Prevention of Heart Disease.

For more information:

• Blaha MJ, Bansal S, Rouf R, et al. A practical “ABCDE” approach to the metabolic syndrome. Mayo Clinic Proceedings. In press.
• LaMonte MJ, Barlow CE, Jurca R, et al. Cardiorespiratory fitness is inversely associated with the incidence of metabolic syndrome. Circulation. 2005;112:505-512.
• Orakzai RH, Orakzai SH, Nasir K, et al. Association of increased cardiorespiratory fitness with low risk for clustering of metabolic syndrome components in asymptomatic men. Arch Med Re. 2006;37:522-528.
• Pollin IS, Kral BG, Shattuck T, et al. High prevalence of cardiometabolic risk factors in women considered low risk by traditional risk assessment. J Womens Health. 2008;doi:10.1089/jwh.2007.0640.
• Tjonnas AE, Lee SJ, Rogonmo O, et al. Aerobic interval training vs. continuous moderate exercise as a treatment for the metabolic syndrome: a pilot study. Circulation. 2008;doi:10.1161/circulationaha.108.772822.