Sitting all day may significantly boost the risk of disease even for those who exercise regularly, say scientists who suggest that our bodies were simply not designed to sit all day.
While we've long been told that sedentary lifestyles are not healthy, many have assumed that maintaining a healthy weight and exercising a few times a week is enough to offset the time spent on our rear ends.
But in a new editorial published in the British Journal of Sports Medicine, Swedish scientists say that may not be true. They say the evidence is mounting that people who sit still for prolonged periods of time -- such as desk workers -- have a higher risk of disease than those who move around during the day, even if both groups still exercise.
Elin Ekblom-Bak of the Swedish School of Sport and Health Sciences in Stockholm suggests that people need to rethink how they define physical activity to highlight the dangers of sitting.
"Sedentary time should be defined as muscular inactivity rather than the absence of exercise," she and her team write.
"We need to consider that we are dealing with two distinct behaviors and their effects."
Her team proposes a new "paradigm of inactivity physiology," and they urge fellow researchers to rethink the definition of "sedentary lifestyle" so that is doesn't just include those who don't exercise but those who spend most of their days in a chair.
Although the relationship between prolonged sitting and poor health and premature death needs to be more clearly understood, researchers say it appears that muscle movement may be crucial because it plays a role in controlling blood fats.
So even people of normal weight who are tied to a desk, their car or glued to their TV most are at risk of health problems, the evidence suggests.
They point to recent research that found that lipoprotein lipase, an enzyme that plays a crucial role in breaking down fat within the body was significantly lower in rats with restrained muscle activity.
The LPL levels in the mice allowed to simply walk about "was not significantly different from that of rats exposed to higher levels of exercise," the scientists reported.
"This stresses the importance of local muscle contraction per se, rather than the intensity of the contraction," they said.
Several recent studies have found that people who spend most of their days sitting are more likely to be overweight, develop heart disease or die prematurely.
For example, a study released last week showed that sitting in front of the TV for hours can raise the risk of early death from heart disease, cancer or any cause.
Another recent study found that a woman's risk of metabolic syndrome, a precursor to diabetes and heart disease, jumps 26 per cent for every extra hour she sits in front of the TV.
The Swedish researchers say that even small bouts of activity through the day can help ward off bad health, even if the activity doesn't raise the heart rate.
They encourage health care practitioners to emphasize the importance of simple, non-exercise activities.
"Climbing the stairs, rather than using elevators and escalators, five minutes of break during sedentary work, or walking to the store rather than taking the car will be as important as exercise," the team said in a news release.
