Leisurely walking for distance combined with low-impact cardiovascular activity appears to be the best formula for obese people seeking to get into shape and stay healthy, according to a University of Colorado at Boulder study.

Ray Browning, a doctoral student in CU-Boulder's integrative physiology department and lead author on the new study, said the results show that people who walk a mile at a leisurely pace burn more calories than if they walk a mile at their normal pace. In addition, those who walk at 2 miles per hour rather than 3 miles per hour reduce the loads on their knee joints by up to 25 percent.

"The message is that by walking more slowly, obese individuals can burn more calories per mile and may reduce the risk of arthritis or joint injury," he said.

Browning and his CU colleagues also found the number of calories burned per pound of body weight is similar for obese adults as normal sized adults walking at the same speed. Because obese people generally have heavier legs, wider stances and swing their legs in a wider arc, the researchers expected the cost of walking for obese people to be significantly higher.

"This was a surprise," said Browning. "The subjects probably are unwittingly altering their posture and walking with straighter legs, conserving calories in the process."

A paper by Browning, CU-Boulder integrative physiology Associate Professor Rodger Kram and undergraduates Emily Baker and Jessica Herron was presented at the June 2005 meeting of the American College of Sports Medicine meeting in Nashville and published recently in the journal, "Obesity Research."

The CU-Boulder researchers based their expectations that obese adults would have a greater energy cost when walking on previous studies by Kram's lab team. In one study, energy expenditure increased by about 25 percent when normal-weight people walked with a deliberately wider stance, said Browning.

Other CU studies conducted in CU's Locomotion Laboratory have shown that normal weight people wearing "winged" shoes designed to force them to increase their lateral leg swing increased the metabolic cost of walking by 30 percent, Browning said.

"As people become gradually obese, they also seem to become particularly graceful," said Kram. "There appears to be some sort of a physiological drive for them to minimize the amount of energy they expend."

The researchers tested 20 men and 20 women on treadmills and sidewalks, half of whom were of normal weight and half classified as class 2 obese, meaning they have a body mass index, or BMI, of 30 to 40. A 5-foot 4-inch tall woman with a BMI of 30 weighs about 175 pounds, while a 6-foot man with a BMI of 30 weighs about 225 pounds.

The researchers measured each subject's body composition using an instrument known as a DEXA scanner to measure fat mass, lean tissue mass and bone mineral content of the total body. They also measured the oxygen consumption and carbon dioxide production of the test subjects to determine the energy and calories expended while walking.

As part of the ongoing research, the research team is using a unique treadmill that can independently measure loads placed on the left and right feet while walking, Browning said. The treadmill helps them measure how the biomechanical forces increase with body weight and walking speed.

The results show that brisk walking dramatically increases the knee joint forces, which can lead to a variety of problems including joint injuries and arthritis, the researchers said.

"This study also pointed up the phenomenal accomplishments of obese people," said Kram. "Our test subjects lead productive lives, and if you weigh 300 pounds, many everyday activities are athletic endeavors."

Walking doesn't require special clothing, stressed Browning. "It's doing some simple things, like using the stairs rather the elevator, parking your car further from your destination, or getting off the bus one stop early and walking. Rather than trying to walk fast, obese individuals can gain both caloric and biomechanical benefits from walking at a more leisurely pace."

Because walking slowly may not significantly improve an obese person's level of cardiovascular fitness, performing other vigorous lower-impact activities like swimming, cycling, step routines and elliptical training workouts also are recommended, said Browning.

Much of the research was carried out at the General Clinical Research Center housed within CU-Boulder's Wardenburg Health Center, which receives more than $1 million in funding annually from the National Institutes of Health.