DURHAM, N.C. -- The amount of exercise may be more important thanintensity to improve cardiovascular health, according to a new analysisof the first randomized clinical trial evaluating the effects ofexercise amount and intensity in sedentary overweight men and women.This finding of the value of moderate exercise should be encouragingnews for those who mistakenly believe only intense exercise can improvehealth, said the researchers who conducted the trial.
The trial, led by researchers at Duke University Medical Center,found that a moderate exercise regimen, such as 12 miles of briskwalking each week, can provide significant improvements in fitnesslevels while reducing the risks of developing cardiovascular disease.Furthermore, the researchers found that any additional increase inamount or intensity can yield even more health benefits.
The results of the analysis were published in the October, 2005, issue of the journal Chest.
"People only need to walk up to 12 miles per week or for about125 to 200 minutes per week to improve their heart health," said thelead author Brian Duscha. "Our data suggest that if you walk brisklyfor 12 miles per week you will significantly increase yourcardiovascular fitness levels compared to baseline. If you increaseeither your mileage or intensity, by going up an incline or jogging,you will achieve even greater gains."
The researchers said that their findings should inspire thosecouch potatoes who have been hesitant to begin exercising regularly --especially since earlier analysis of the same participants (will insertlink to inactivity study) by the same Duke team found that people whodo not exercise and maintain the same diet will gain up to four poundseach year.
"The participants in our study received the fitness benefitswithout losing any weight," Duscha said. "Many people exercise to loseweight, and when that doesn't occur, they stop exercising. However, thetruth is that you can improve cardiovascular fitness and reduce therisk of heart disease by exercising without losing weight."
To better understand the effects of differing amounts ofexercise, the researchers studied 133 overweight sedentary men andwomen who were beginning to show signs of blood lipid levels highenough to affect their health. They were randomized into one of fourgroups: no exercise, low amount/moderate intensity (equivalent of 12miles of walking per week), low amount/vigorous intensity (12 miles ofjogging per week) or high amount/vigorous intensity (20 miles ofjogging per week).
Since the trial was designed solely to better understand therole of exercise, patients were told not to alter their diet during thecourse of the trial, which lasted six months for the group that did notexercise or eight-months for the exercise groups. The additional twomonths for the exercise group came at the beginning of trial, whenparticipants slowly ramped up their exercise to their designatedlevels. The exercise was carried out on treadmills.
For their analysis, the team compared two measurements offitness -- peak VO2 and time to exhaustion (TTE) -- before and afterthe trial. Peak VO2 is a calculation that measures the maximum amountof oxygen that can be delivered by circulating blood to tissues in agiven period of time while exercising.
While all the exercise groups saw improvements in peak VO2 andTTE after completing their exercise regimens, the researchers noticedsome interesting trends.
"We found that when we compared the low amount/moderateintensity group to the low amount/vigorous intensity group, we did notsee a significant improvement in peak oxygen consumption," Duscha said."However, when we increased the amount of exercise from 12 to 20 miles-- at the same intensity -- we did see an improvement in peak oxygenconsumption."
Also, although no statistically significant difference wasdetected between the low amount/moderate intensity group and the lowamount/high intensity group, the researchers did see a trend towardboth a separate and combined effect of exercise intensity and amount onincreased peak VO2 levels.
The Duke team was led by cardiologist William Kraus, M.D., whoreceived a $4.3 million grant from the National Heart, Lung and BloodInstitute in 1998 to investigate the effects of exercise on sedentaryoverweight adults at risk for developing heart disease and/or diabetes.The results of that five-year trial, known as STRRIDE (Studies ofTargeted Risk Reduction Interventions through Defined Exercise), andother analyses of the data collected, began to be published in 2002.
The Duke team is currently enrolling patients in STRRIDE II, inwhich researchers are seeking to determine the effects of weighttraining, alone and in combination with aerobic training, oncardiovascular health.
Joining Duscha were Duke colleagues Cris Slentz, Ph.D., JohannaJohnson, Daniel Bensimhon, M.D., and Kenneth Knetzger. Joseph Houmard,Ph.D., East Carolina University, was also a member of the team.
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