The amount of exercise may be more important than intensity to improve cardiovascular health, according to a new analysis of the first randomized clinical trial evaluating the effects of exercise amount and intensity in sedentary overweight men and women.
This finding of the value of moderate exercise should be encouraging news for those who mistakenly believe only intense exercise can improve health, 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 brisk walking each week, can provide significant improvements in fitness levels while reducing the risks of developing cardiovascular disease. Furthermore, the researchers found that any additional increase in amount 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 about 125 to 200 minutes per week to improve their heart health," said the lead author Brian Duscha. "Our data suggest that if you walk briskly for 12 miles per week you will significantly increase your cardiovascular fitness levels compared to baseline. If you increase either 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 those couch potatoes who have been hesitant to begin exercising regularly -- especially since earlier analysis of the same participants (will insert link to inactivity study) by the same Duke team found that people who do not exercise and maintain the same diet will gain up to four pounds each year.
"The participants in our study received the fitness benefits without losing any weight," Duscha said. "Many people exercise to lose weight, and when that doesn't occur, they stop exercising. However, the truth is that you can improve cardiovascular fitness and reduce the risk of heart disease by exercising without losing weight."
To better understand the effects of differing amounts of exercise, the researchers studied 133 overweight sedentary men and women who were beginning to show signs of blood lipid levels high enough to affect their health. They were randomized into one of four groups: no exercise, low amount/moderate intensity (equivalent of 12 miles of walking per week), low amount/vigorous intensity (12 miles of jogging per week) or high amount/vigorous intensity (20 miles of jogging per week).
Since the trial was designed solely to better understand the role of exercise, patients were told not to alter their diet during the course of the trial, which lasted six months for the group that did not exercise or eight-months for the exercise groups. The additional two months for the exercise group came at the beginning of trial, when participants slowly ramped up their exercise to their designated levels. The exercise was carried out on treadmills.
For their analysis, the team compared two measurements of fitness – peak VO2 and time to exhaustion (TTE) – before and after the trial. Peak VO2 is a calculation that measures the maximum amount of oxygen that can be delivered by circulating blood to tissues in a given period of time while exercising.
While all the exercise groups saw improvements in peak VO2 and TTE after completing their exercise regimens, the researchers noticed some interesting trends.
"We found that when we compared the low amount/moderate intensity group to the low amount/vigorous intensity group, we did not see 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 oxygen consumption."
Also, although no statistically significant difference was detected between the low amount/moderate intensity group and the low amount/high intensity group, the researchers did see a trend toward both a separate and combined effect of exercise intensity and amount on increased peak VO2 levels.
The Duke team was led by cardiologist William Kraus, M.D., who received a $4.3 million grant from the National Heart, Lung and Blood Institute in 1998 to investigate the effects of exercise on sedentary overweight adults at risk for developing heart disease and/or diabetes. The results of that five-year trial, known as STRRIDE (Studies of Targeted Risk Reduction Interventions through Defined Exercise), and other analyses of the data collected, began to be published in 2002.
The Duke team is currently enrolling patients in STRRIDE II, in which researchers are seeking to determine the effects of weight training, alone and in combination with aerobic training, on cardiovascular health.
Joining Duscha were Duke colleagues Cris Slentz, Ph.D., Johanna Johnson, Daniel Bensimhon, M.D., and Kenneth Knetzger. Joseph Houmard, Ph.D., East Carolina University, was also a member of the team.