An Idle Body Doesn’t Make a Healthy Body

Sedentary behavior linked to lower levels of cardiorespiratory fitness

(RxWiki News) Even with daily workout sessions, too much sitting can jeopardize your overall health, according to new research.

A recent study found that individuals who spent more time being sedentary (physically inactive) also had lower cardiorespiratory fitness—meaning their bodies were not as efficient in pumping oxygen to their muscles during exercise as individuals who were less sedentary.

The study authors noted that the negative effect of sitting for six to seven hours per day was similar to the positive effect of one hour of moderately intense exercise.

"Set a goal to stand, walk and stretch every hour."

This research study was led by Jarrett D. Berry, MD, MS, at UT Southwestern Medical Center. The research team examined the relationship between cardiorespiratory fitness and sedentary behavior.

Cardiorespiratory fitness refers to how well a person is able to pump blood and oxygen to the muscles while doing exercise. Individuals who regularly exercise have hearts that can pump blood and oxygen to the muscles more efficiently than the hearts of individuals who don’t engage in regular exercise.

Sedentary behavior included activities that required little energy to complete including sitting, watching television, reading and driving.

Data was analyzed from 2,223 participants between the ages of 12 and 49 years old who participated in the National Health and Nutrition Examination Survey from 2003-2004. Participants were excluded if they:

  • had a history of heart disease
  • had any physical limitations that would prevent them from using a treadmill
  • had asthma or other lung and breathing conditions
  • were more than 12 weeks pregnant
  • were using medications that affected the heart, including beta blockers (slow down heart beat) and anti-arrhythmic agents (regulates heart beat)

Study participants were asked to wear an accelerometer (a device that measures motion) for seven consecutive days except while sleeping and when doing water-based activities (e.g. swimming or bathing). Data from the accelerometer would reveal when participants were being sedentary and when they were being active.

Using age, gender and body mass index (a measure of height and weight) as a guide, researchers assigned each participant to one of eight treadmill tests to determine cardiorespiratory fitness level. Each test included a two minute warm-up, two three-minute exercise segments, and a two minute cool-down. During these tests, heart rate was monitored and blood pressure was measured at the end of each segment.

Participants were asked to classify their typical daily activity into one of the following four groups: sits during the day and does not walk very much, stands or walks frequently during the day, but does not have to carry or lift things often, lifts light loads or has to climb hills or stairs often, and does heavy work or carries heavy loads.

They were also asked to report their current smoking status.

Several factors were taken into account when analyzing their findings including age, gender, body mass index, current smoking status and cholesterol levels.

The researchers found that on average, women were more sedentary than men, spending about seven hours per day being sedentary, while men spent on average 6.6 hours per day being sedentary. Women were also found to spend less time engaged in moderate and vigorous physical activity (7.8 minutes per day) compared to men (16.8 minutes per day)

Based on the length and intensity of physical activity, the researchers determined a metabolic equivalent task (MET) score for participants. MET is the ratio of calories that the body burns during an activity to calories that the body burns at rest. A 4-MET activity, for example, burns four times the amount of calories than what the body burns while at rest.

The researchers found that an extra hour of daily exercise activity time was associated with a 0.88 unit increase in MET score for men and a 1.37 unit increase in MET score for women.

An additional hour of sedentary time, however, was associated with a 0.12 unit decrease in MET score for men and a 0.24 unit decrease in MET score for women.

The study authors noted that for those with lower fitness levels, more time spent engaging in sedentary behavior, adds to the problem and has a greater negative effect on health.

They concluded that along with regular exercise, limiting sedentary behavior such as sitting or watching tv, may be a potential strategy to improve health.

"We've known for some time that regular exercise has health benefits. Unfortunately, if it's followed by several hours of physical inactivity, we don't reap the benefits that we had worked so hard to receive," said Rusty Gregory, a wellness coach, personal fitness trainer and author of "Self-Care Reform: How to Discover Your Own Path to Good Health" and "Living Wheat-Free For Dummies."

"Staying active throughout the day ensures that we are doing everything we can from a physical activity standpoint to reach optimal health," Gregory told dailyRx News.

Gregory offered some ideas to increase activity levels:

1. Take the stairs, not the elevator.
2. Park farther away and walk to your destination.
3. Perform exercises throughout the day if you find yourself sedentary for long periods of time.
4. Look for ways to be more physically active, like family bicycle rides, playing with your children or taking your dog for a walk.

This study by Dr. Berry and team was published on July 7 in Mayo Clinic Proceedings.

Some of the study authors reported competing interests with companies including Astra Zeneca, Technogym and Novo Nordisk.

Review Date: 
July 13, 2014