Sedentary time, not just lack of exercise, detrimental to fitness
A new report published in Mayo Clinic Proceedings indicates that 1 hour of daily exercise increased fitness in men and women, while an hour of sedentary time decreased overall cardiorespiratory fitness.
In an interview with Cardiology Today, Jarett D. Berry, MD, MS, assistant professor of internal medicine and clinical science at UT Southwestern Medical Center, said, “We asked to what extent sitting could be associated with lower exercise capacity. If we think about the benefit of exercise, part of it is not only risk factor reduction, but also an improvement in our exercise capacity.”
Jarett D. Berry
Using data from the National Health and Nutrition Examination Survey 2003-2004, Berry and colleagues studied the activity levels of 2,223 participants aged 12 to 49 years (mean 22 years) who each wore an accelerometer for at least 1 day and self-reported their normal activity levels. Measurements of CV fitness indicators were taken, including BP, lipid profiles, blood glucose, smoking status and BMI. Cardiorespiratory fitness was determined using an exercise treadmill test and categorized as low, moderate or high.
Compared with those in the high fitness group, those with low fitness tended to report more sedentary time and spent less time exercising. Men with low fitness scores spent 36 more minutes being sedentary each day compared with those with high fitness scores (7 hours vs. 6.4 hours; P<.001) and engaged in 8 fewer minutes of exercise each day (12 minutes vs. 19.8 minutes; P<.001). According to researchers, results were similar among women.
“With exercise capacity, as expected, more exercise time is associated with higher fitness, but even when you account for that, more sitting time is associated with lower fitness,” Berry said. “These data appear to suggest that prolonged sitting may be detrimental to heart health through its impact on exercise capacity.”
Participants were separated into four groups: those who sit during the day and do not walk much, those who stand or walk frequently during the day but without lifting or carrying objects, those who lift light loads or have to climb stairs or hills frequently, and those who do heavy work or carry heavy loads. Researchers observed that the negative impact on fitness from sitting for 6 to 7 hours per day was of the same magnitude as the positive impact of 1 hour of exercise per day.
“We’ve known for decades that we should exercise, but there is a theme in the literature suggesting that sitting too much can harm one’s health. What isn’t known is the mechanisms through which sitting might be associated with CV risk,” Berry said.
More research needs to be conducted, Berry added.
“Going forward, these data suggest more work needs to be done to understand this connection between sitting and exercise capacity. More importantly, many of the questions that have been raised by this are questions that can really only be answered in the context of a randomized clinical trial.” – by Shirley Pulawski
Disclosure: See the full study for a complete list of relevant financial disclosures.