Several studies have shown that a sedentary lifestyle is associated with higher overall and cardiovascular mortality. People who do not do enough physical activity have a higher mortality rate due to cardiovascular disease, but people who do physical exercise and have a very sedentary overall behavior also have a higher mortality rate. This has led to the development of programs against sedentary lifestyles in some countries.
Adults are advised to minimize the amount of time spent in sedentary activities over prolonged periods. Sedentary behavior is assumed to be an independent risk factor for health. This recommendation is probably appropriate, but there are uncertainties about the association between sedentary time and health, the cause of the association, and the relationship between quantity and response.
Definition of sedentary
One of the first questions that arises is the definition of “sedentary,” which etymologically means “staying seated in one place.” Excessive sedentary behavior has been defined as a person who does not engage in moderate to vigorous physical activity.
However, given the evidence that sedentary time is a risk factor, the definition of sedentary behavior should be distinct from just the lack of moderate to vigorous physical activity.
One of the definitions that has been suggested for sedentary lifestyle is that of waking behavior characterized by an energy expenditure ≤1.5 metabolic equivalents, with a metabolic equivalent equal to 3.5 ml of oxygen consumed per kilogram of body weight per minute.
Assessment of sedentary lifestyle
In Western countries, people spend 6 to 8 hours on sedentary behaviors, mainly sitting at work, watching television, movies, the computer, reading, eating or traveling.
When assessing sedentary behavior, one of the main problems that arises is its measurement. Sedentary behavior has traditionally been assessed through surveys or direct observation, but specific measuring devices are increasingly being used, which are more objective.
It has been claimed that measuring devices are the ones that should really be considered when assessing sedentary behavior. However, some studies have shown that the information provided by the individual is important, as it allows us to know the causes, places, and situations that condition sedentary behavior.
Accelerometers have been the most widely used devices to objectively measure the degree of sedentary behavior. Accelerometers measure acceleration, which is defined as the change in the speed of movement. The movement detected by accelerometers is converted into electrical signals or “counts,” which are typically displayed as a percentage of total time or by hours per day.
Logically, accelerometers are not completely effective, as they can overestimate the degree of sedentary lifestyle if they do not record some movements. They depend on their detection system and the place on the body where they are placed, which can be on the wrist, waist or other parts of the body. In order to try to overcome this drawback, devices with new detection systems are being investigated.
The thresholds for accelerometer measurements to consider a behavior as sedentary are not well-defined. A cutoff point that has been proposed to quantify the time of sedentary behavior is less than 100 counts per minute, mainly using waist-worn accelerometers. Devices worn on the wrist or ankle may require different thresholds, which are not well-defined because these techniques are still being evaluated.
Sedentary lifestyle and risk
Sedentary behavior has been linked to the development of obesity, hypercholesterolemia, and diabetes. As mentioned above, sedentary behavior is associated with increased cardiovascular mortality, and has therefore been considered another risk factor. It has also been associated with increased overall mortality, including a higher incidence of cancer.
Logically, the first step to take to reduce sedentary lifestyle is to recommend regular physical exercise, which is the classic recommendation for this purpose. However, given that people can have a very sedentary behavior despite practicing a sport every day, actions to reduce sedentary behavior must be extended to other levels.
The sedentary behaviors that have been most prominent in studies are television viewing and low activity in the workplace. Therefore, interventions with adults to reduce sedentary behavior have focused primarily on targeting these behaviors, encouraging movement during sedentary times and avoiding prolonged sitting.
Various methods have been proposed to reduce sedentary time, but the goal has always been to move around rather than sit for long periods of time. Getting up and moving around for 3 minutes for every 30 minutes of sitting has been recommended, which seems to be the best, although breaks could be made for 6 minutes for every 60 minutes of sitting. It is possible that the more frequent the breaks from sedentary time, the more effective they may be.
Conclusion
In conclusion, sedentary time is a risk factor for mortality, so it should be reduced as much as possible. It is not just about doing physical exercise daily, which is recommended at least 30 minutes on 3 days of the week, but also about interrupting sedentary times, avoiding prolonged sitting, if possible no more than 30 minutes at a time.
