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Study: Obese Adults More Fit Than Previously Thought

DALLAS — Dallas researchers have found that otherwise healthy obese adults are more fit than previously thought and say physicians should not use traditional methods of determining the fitness level of their overweight or obese patients.

The scientists at the Institute for Exercise and Environmental Medicine (IEEM) at Texas Health Presbyterian Hospital Dallas say these findings could help overweight or obese Americans establish more appropriate exercise regimes.

“Obesity is one of the most important health challenges of the 21st century,” said Santiago Lorenzo, Ph.D., a cardiopulmonary researcher at the IEEM, which is a joint collaboration between Texas Health Dallas and UT Southwestern Medical Center. “Exercise is an important component in the prevention and treatment of obesity, making it critical that we accurately measure people’s cardiorespiratory fitness level, which can help people find their most optimal workout intensities and the best types of exercise for losing weight and improving overall fitness.”

Tony G. Babb, Ph.D.
Tony G. Babb, Ph.D.
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The cardiorespiratory system is made up for the body’s cardiovascular system (heart and blood vessels), combined with the respiratory system (respiratory muscles, lungs and airways). The cardiorespiratory system transports the air a person breathes into the bloodstream and circulates it throughout the body, supplying oxygen to muscles and organs, and removing waste products.

In recent years, researchers at the IEEM have become foremost experts in obesity, respiratory function, overall cardiorespiratory fitness and exercise tolerance. Their work has been published in numerous peer-reviewed scientific journals.

“It’s usually assumed that obese people are unfit, but that’s not true,” said Tony G. Babb, Ph.D., director the IEEM’s cardiopulmonary laboratory and principal investigator on the NIH sponsored project. “We’ve found that their cardiorespiratory systems are usually within normal limits.”

The traditional method to measure a person’s cardiorespiratory fitness level is called V•O2max, which represents the highest rate of oxygen the body utilizes during a maximal effort. The test involves a person undergoing increased efforts as they ride a stationary bike (by increasing resistance), or run on a treadmill (by increasing speed and/or grade). Scientists estimate V•O2 max by measuring the volume of air that the person breaths (ventilation) and the gas concentrations (oxygen, carbon dioxide) in the inspired and expired air. Competitive athletes commonly use V•O2max to determine their fitness levels and preparedness for upcoming competitions.

“But the test has also been widely used to measure the fitness level of non athletes, including obese adults who are often encouraged to take the tests by their physicians before starting an exercise program,” Lorenzo said.

In their recent paper, the IEEM researchers found that healthy obese adults were penalized (i.e. show lower V•O2max values than nonobese) when using traditional methods of reporting V•O2max (relative to their body weight or lean body mass), resulting in an inadequate assessment of their cardiorespiratory fitness. Their paper, “Quantification of cardiorespiratory fitness in healthy nonobese and obese men and women,” appears in the journal Chest.

“Without an acceptable way of assessing cardiorespiratory fitness, physicians can’t determine if an obese patient who has shortness of breath during exercise is simply deconditioned or suffering from an underlying medical issue,” Babb said.

The IEEM researchers found that the V•O2max test underestimates cardiorespiratory fitness in healthy obese adults when it’s expressed relative to overall body weight. When expressed relative to lean body mass, researchers found the test may be a better approach in mildly obese people, except when there is a significant increase in muscle mass as in moderate-to-extreme obese individuals. In fact, the researchers found that some of the obese subjects actually had higher than expected cardiorespiratory fitness levels, which scientists think could be from higher amounts of muscle.

The IEEM researchers say physicians should use existing predictive equations for patients, rather than using the traditional methods that report V•O2max relative to body weight or lean body mass. Predicted V•O2max using those equations factor in age, gender and predicted weight (based on height) and allow for adequate assessment and comparisons of cardiorespiratory fitness among obese as well as nonobese individuals. When overweight individuals undergo an exercise test, their physicians should be aware of this information to better evaluate what their true exercise capacity should be, the researchers found.

The study measured maximal cardiorespiratory function in 19 nonobese and 66 obese adults. The study participants underwent hydrostatic weighing to accurately measure their body composition (i.e. amount of lean body mass and fat mass). Their V•O2max was then measured while riding a stationary bike.

“Our results don’t mean an obese person can go out and run a 4-minute mile,” Lorenzo said. “It means their cardiorespiratory system is probably functioning fairly well and there’s probably not a reason they can’t get out and exercise. That’s really good news for obese individuals who want to be active and take part in an exercise program for weight loss or improving overall fitness.”

About the Institute for Exercise and Environmental Medicine
The Institute for Exercise and Environmental Medicine (IEEM) was founded as a joint program between Texas Health Presbyterian Hospital Dallas and UT Southwestern Medical Center. Its mission is to promote basic and clinical research, education, and clinical practice in defining the limits to human functional capacity in health and disease, with the objective of improving the quality of life for human beings of all ages. The IEEM includes ten major laboratories tightly integrated and organized intellectually along the “oxygen cascade” — the path that oxygen must follow through the body from the external environment through the lungs, heart, skeletal muscles, and brain to perform cognitive function and physical activity. The IEEM is among the few research centers in the world that fosters the fusion of basic science and clinical medicine in a program designed specifically to study human physiology.

About Texas Health Presbyterian Hospital Dallas
Texas Health Presbyterian Hospital Dallas is an 898-bed acute care hospital and recognized clinical program leader, having provided compassionate care to the residents of Dallas and surrounding communities since 1966. U.S. News and World Report has ranked Texas Health Dallas among the nation’s best hospitals in digestive disorders, orthopedics, and neurology and neurosurgery. An affiliate of the faith-based, nonprofit Texas Health Resources system, Texas Health Dallas has approximately 4,000 employees and an active medical staff of more than 1,000 physicians. For more information, call 1-877-THR-WELL, or visit

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