Sedentariness: A need for a definition
- 1UMR6024 Laboratoire de Psychologie Sociale et Cognitive (LAPSCO), France
- 2Preventive and Occupational Medicine, Centre Hospitalier Universitaire de Clermont-Ferrand, France
Sedentary behavior is acknowledge as a public health concern (1). However, the definition of sedentary behavior might not be enough to reveal the growing importance and the complexity of the sedentary lifestyle. Indeed, the terminology consensus projects from the sedentary behavior research network (SBRN) defines sedentary behavior as “any waking behavior characterized by an energy expenditure ≤1.5 metabolic equivalent of task (METs), while in a sitting, reclining or lying posture” (2). Yet, this definition refers to behaviors adopted at a precise moment in time. Thus, it doesn’t grant a better understanding of what a sedentary lifestyle is and what its features are. In the case of physical activity, there is a definition based on recommendations that distinguishes inactive and active individuals. It is known that practicing less than 150 minutes of moderate physical activity or 75 minutes of vigorous physical activity per week is considered as physical inactivity (i.e. a lack of physical activity) since it is detrimental to health (3). However, there is not such definition nor recommendation in the case of sedentary behaviors despite being independent of physical activity (4). Such definition would have a beneficial impact on the lifestyle in modern societies. In order to achieve those recommendations more studies are needed to define cut-offs that would determine the safe amount of sedentary behavior per day taking into consideration that it is especially prolonged and interrupted sedentary behaviors which are deleterious to health (1).
Sedentary behavior has been defined in many ways over the years (5). It has been mostly defined by energy expenditure (e.g., any behavior where the energetic expenditure is strictly below 2 METs (6), or between 1 MET and 1.8 METs (7)). That criterion alone was problematic since standing still has an energy cost close to sitting (8) without causing the detrimental health effects of sedentary behaviors (9). For instance, breaking up prolonged sitting time by standing during few minutes has a positive impact on postprandial glucose metabolism (9–11). It is essential to alternate posture and not sitting for prolonged periods of time (1). Of course, it is also true that standing for long periods is detrimental (12) that’s why the best adjustment in alternating postures should be investigated. Then, posture has been taken into consideration to clarify any ambiguities regarding the categorization of standing as sedentary or not. That makes sense since sedentary comes from the latin term “sedere” which means “to sit”. A recent consensus project by SBRN proposed that sedentary behavior can be defined as ““any waking behavior characterized by an energy expenditure ≤1.5 metabolic equivalent of task (METs), while in a sitting, reclining or lying posture”. Thus, this definition being based on both posture and energy expenditure excludes standing from sedentary behavior and grant a better understanding of what is a sedentary behavior and what distinguished those activities from others.
However, the definition proposed by the SBRN reflects only behaviors adopted at a specific moment in time. At a point in time, it seems that only METs scores and posture distinguish sedentary behaviors from physical activity. Although when the lifestyle is considered, energy expenditure and posture are not enough, it is necessary to include length, duration and interruption of those behaviors. In the case of Physical inactivity, it is define as a lack of physical activity, an insufficient energy expenditure (2,13) characterized by the minimum quantity of moderate or intense physical activity recommended per week (cf. World Health Organization recommendations (14)). Yet, around one third of the world’s population do not respect these recommendations (15,16). Fifty-five to 70% of Americans over the age of 65 seemingly do not appear to achieve the minimum recommended physical activity (16,17). According to the WHO recommendations (17), an adult aged between 18 and 64 should do at least 150 minutes of moderate physical activity per week or 75 minutes of intense physical activity per week (3,14). This physical activity should be performed in periods of at least 10 minutes within the week (18,19). However, there is not such definition to refer to a sedentary lifestyle. It is well known that people who practiced physical activity under those recommendations are considered as physical inactive since that this lack of physical activity is detrimental to health (3). Yet, the definition of recommendation for physical activity cannot reflect what a sedentary lifestyle is, since that physical inactivity and sedentary behavior are independent (4) even if some authors tend to confuse both notions (20–22).
Indeed, according to this definition of physical inactivity (i.e., practicing less than 150 minutes of moderate physical activity or 75 minutes of vigorous physical activity per week), it would correspond to one extremity of the physical exercise spectrum, with the other extremity corresponding to the practice of a regular and intense physical activity. But sedentariness can be an independent factor of physical activity (4,21), because it would have effects on health independent to those of physical activity (4,23–27). Thus, to adopt sedentary behaviors leads to an increased risk of mortality and morbidity, irrespective of the quantity of moderate or physical activity practiced (4,22). It is therefore important to differentiate physical inactivity from sedentariness. Though, what does it mean to be considered as sedentary? What is sedentariness as a way of life? How long humans need to sit per day to be considered as sedentary? Does sedentary time need to be uninterrupted to describe sedentary lifestyle? At the best of our knowledge, consensual answers to those questions are still missing. Thus, the definition of sedentary behavior might not be enough to reflect the social and health importance of the sedentary lifestyle into our modern societies and there would be a need to define sedentariness as a way of life.
Such definition, being complementary to the definition of sedentary behavior at a specific moment (2), would have a beneficial impact on the modern lifestyle since we would be able to give recommendations (as the ones existing for physical activity) to improve this way of life by making it healthier. This definition would have to be based on recommendations which need to be determined by cut-offs reflecting the total amount of sedentary time above which deleterious health effects appear as it was done for physical inactivity (i.e. at least 150 minutes of moderate physical activity per week or 75 minutes of intense physical activity per week (3,14)). Those health effects seem to arise only after a prolonged and uninterrupted exposure to those sedentary lifestyle and behavior. Regarding the duration of sedentary time per week, cut-offs have been proposed to define a sedentary lifestyle but there are still no consensus. Indeed, several studies have identified deleterious health consequences of sitting more than 4 (28,29), 7 (30) or 8 (31,32) hours per day. Another factor needs to be considered which is the interruption of sedentary bouts. Health benefits were demonstrated by breaking sedentary behavior every 20 (10,33), or 30 (34–37) minutes. Yet there is not a consensus for how often is it preferable to break up sedentary time. Therefore, consensual cut-offs should be define for both sedentary lifestyle and maximal duration of sedentary bouts in order to proposed a definition of sedentariness as a way of life in addition of the existing definition of sedentary behaviors at a point in time.
Sedentary behavior is a topic of importance nowadays (1). The consequences of adopting a sedentary behavior at a specific moment, in the short term, are more and more understood and known, especially regarding physiological factors. Although, when the accumulation of sedentary behavior over the years, the lifestyle, is considered new questions arise. In the long-term sedentariness as a way of life might have detrimental consequences not only on the physiological level but also on others aspects that would determine life quality and well-being. Therefore, there a need for a definition of sedentariness as a way of life that would provide a better understanding of this lifestyle and its implications on physiological, psychological and social levels.
Keywords: Sedentariness, physiacl activity, Health, Sitting, standing, sedentary behavior
Received: 06 Jul 2018;
Accepted: 04 Dec 2018.
Edited by:Daniel P. Bailey, University of Bedfordshire Bedford, United Kingdom
Reviewed by:Céline Aguer, Institut du savoir Montfort (ISM), Canada
Copyright: © 2018 Magnon, Dutheil and Auxiette. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Dr. Catherine Auxiette, UMR6024 Laboratoire de Psychologie Sociale et Cognitive (LAPSCO), Clermont-Ferrand, France, email@example.com