The American Heart Association and other advisory groups recommend that all Americans regularly participate in moderate-to-vigorous exercise that boosts the heart rate to more than 55 percent of its maximum.
"A large segment of the population still believes exercise must be vigorous, demanding or involve more complicated activities than walking to adequately raise one's heart rate. This perception of 'no pain, no gain' can discourage people from starting to exercise at all," said lead investigator Kyle McInnis, Sc.D., professor of exercise science at the University of Massachusetts in Boston.
The researchers studied 84 obese adults (72 women, 12 men, average age 41), who were seeking professional advice on a safe level of exercise.
"These were middle-aged people like many others. They were between 30 and 100 pounds overweight, with below-average aerobic endurance, and had been thinking about starting to exercise and lose some weight," McInnis said.
At the first visit, researchers measured heart rate and oxygen use, while the subjects walked on a treadmill with a gradually increasing steepness until they felt fatigued.
On a different day, the subjects walked one mile on the treadmill with instructions to maintain a "brisk but comfortable" pace. Participants completed the walk in an average of 18.7 minutes, at an average speed of 3.2 miles per hour.
During the self-paced walk, all the participants achieved the recommended levels of exercise intensity, based on their previous heart rate measures. Thirteen were at moderate intensity (55-69 percent of maximum heart rate), 58 at hard intensity (70-89 percent) and 13 at very hard intensity (90-100 percent).
"Comparison with the treadmill tests showed that when participants self-selected a speed that was comfortable but brisk, their heart rate and level of exertion was in a safe range but high enough to improve their cardiovascular fitness," McInnis said. "You really can get your heart rate up to the level that your doctor would recommend, and you don't have to jog or run to do it."
McInnis hopes these results encourage sedentary people to begin exercising.
"Walking is commonly identified as the single most enjoyable form of recreational exercise. Our study asked whether walking at a self-selected, comfortable pace is adequate to elicit the cardiovascular response associated with improved health and fitness," he said.
The American Heart Association, the Centers for Disease Control and Prevention and the American College of Sports Medicine suggest people walk or perform other moderate-intensity exercises for at least 30 minutes five days or more a week.
Being able to give simple advice on walking may get more physicians talking to their patients about the importance of physical activity. Currently, only about one in three physicians counsels patients about exercise, McInnis said.
The message is particularly important for the growing segment of the population that is overweight or obese. Obesity is a major independent risk factor for heart disease. Most obese persons have one or more additional risk factors, such as high blood pressure, high cholesterol or insulin resistance.
"Increasing physical activity is key to reducing these risks. Even if weight stays the same - and physical exercise is a big help in reducing excess weight - physical activity can improve blood pressure, blood glucose and cholesterol levels, and significantly lower the risk of death and disability from heart disease," McInnis said.
Co-authors are Justin Fiutem, M.S.; Heather Williams, B.S.; Barry Franklin, Ph.D. and James Rippe, M.D.