Extended sedentary behaviour of two hours or more could be as harmful to fitness levels as short stints of exercise are beneficial, a team of cardiologists at the University of Texas Southwestern Medical Center has concluded.
In parallel, six hours spent sitting is as harmful to cardiorespiratory fitness as one hour of exercise is beneficial, according to the study, which considers sedentary activities to be sitting, driving, Internet surfing and reading.
While sedentary behaviour has long been under attack by health-care professionals, the study breaks ground in understanding its pathways.
"Previous studies have reported that sedentary behaviour was associated with an increased risk for cardiovascular outcomes," says Dr. Jarett Berry, Assistant Professor of Internal Medicine and Clinical Science and senior author of the study. "However, the mechanisms through which this occurs are not completely understood."
Using data from 2,223 participants in the U.S. National Health and Nutrition Examination Survey (NHANES), researchers examined cardiorespiratory fitness levels in relation to exercise and the amount of time spent sedentary.
Participants included men and women between the ages of 12 and 49 with no known history of heart disease, asthma or stroke, and their fitness levels were assessed by means of a submaximal treadmill test, adjusting for differences in gender, age and body mass index.
They concluded that in measuring fitness levels, sedentary activity should be considered independent of exercise.
"Our data suggest that sedentary behaviour may increase risk through an impact on lower fitness levels," says Dr. Berry. "And that avoiding sedentary behaviour throughout the day may represent an important companion strategy to improve fitness and health, outside of regular exercise activity."
Researchers say desk workers should feel free to fidget, hoping their study will lead to a common understanding in the workplace about the need to avoid sedentary behavior.
"We also found that when sitting for prolonged periods of time, any movement is good movement, and was also associated with better fitness," said Dr. Jacquelyn Kulinski, a recent graduate from the UT Southwestern Cardiology Fellowship Training Program and first author of the paper. "So if you are stuck at your desk for a while, shift positions frequently, get up and stretch in the middle of a thought, pace while on a phone call, or even fidget."
The study was published in the online edition of the Mayo Clinic Preceedings.
Previously, the Mayo Clinic has advised desk workers to take breaks every 20 to 30 minutes, taking deep breaths to relieve muscle tension, and standing up to take phone calls.
Adding to the list of ways to avoid extended sedentary behaviour, UT Southwestern preventative cardiologists recommend purchasing a pedometre to track daily motion and replacing one's desk chair with a fitness ball.
