(LifeWire) - After years of equating decreased body weight with increased health, things are starting to get more complicated. Recent research suggests that being thin doesn't necessarily mean you're "fit." The opposite can be true as well: being overweight doesn't always mean you're in poor cardiovascular shape. Experts say that the key issue is "cardiovascular fitness."
The National Health and Nutrition Examination Survey (NHANES), a national health survey conducted by the Centers for Disease Control and Prevention, defines cardiovascular fitness as the body's ability to take in, distribute and use oxygen.
The heart and blood system are central to this process. Simply put, the more effectively your heart pumps blood -- and therefore oxygen -- to your muscles and organs, the greater your cardiovascular fitness. The best indicator of cardiovascular fitness is your VO2 max, also termed maximal oxygen uptake or aerobic power.
What you look like on the outside may not reflect your cardiovascular fitness. For example, a 2007 study in the Journal of the American Medical Association found that individuals who are overweight but active can have better cardiovascular fitness than those who are thin but inactive.
Additional findings suggest that being thin doesn't rule out hidden fat that may surround internal organs. Studies funded by Britain's Medical Research Council have found that seemingly healthy, slim individuals may actually carry around internal fat that can lead to conditions, such as diabetes and heart disease.
Just because you get out and walk several times a week, however, doesn't give you a cardiovascular pass to pack on the pounds. A 2008 Harvard study in the Archives of Internal Medicine concluded that "even high levels of physical activity did not eliminate the excess risk of [coronary heart disease] associated with overweight and obesity."
To assess your own cardiovascular fitness you may want to try a simple VO2 max test. Ultimately, you may want to start heart rate training to increase cardiovascular fitness and weight loss, but remember, always consult a physician before beginning an exercise program.
How much exercise is really necessary to improve cardiac health? Read about it here.
"National Health and Nutrition Examination Survey: Cardiovascular Fitness Procedures Manual." cdc.gov. Jan 2004. Centers for Disease Control and Prevention. 6 Oct 2008. <http://www.cdc.gov/nchs/data/nhanes/cv.pdf>.
"Overweight? You Might Not Know It." mrc.ac.uk. 11 Dec 2006. Medical Research Council. 6 Oct 2008. <http://www.mrc.ac.uk/NewsViewsAndEvents/News/MRC003439>.
Sui, Xuemei, Michael J. LaMonte, James N. Laditka, James W. Hardin, Nancy Chase, Steven P. Hooker, and Steven N. Blair. "Cardiorespiratory Fitness and Adiposity as Mortality Predictors in Older Adults." Journal of the American Medical Association. 298:21 (2007): 2507-16. 6 Oct 2008. <http://jama.ama-assn.org/cgi/content/full/298/21/2507>.
Weinstein, Amy R., Howard D. Sesso, I-Min Lee, MBBS, Kathryn M. Rexrode, Nancy R. Cook, JoAnn E. Manson, Julie E. Buring, and J. Michael Gaziano. "The Joint Effects of Physical Activity and Body Mass Index on Coronary Heart Disease Risk in Women." Archives of Internal Medicine. 168 (2008): 884-90. 6 Oct 2008. <http://archinte.ama-assn.org/cgi/content/full/168/8/884>.