CONTEXT: Sparse data exist on the combined associations between physical activity and sedentary time with cardiometabolic risk factors in healthy children.

OBJECTIVE:To examine the independent and combined associations between objectively measured time in moderate- to vigorous-intensity physical activity (MVPA) and sedentary time with cardiometabolic risk factors.

DESIGN, SETTING, AND PARTICIPANTS: Pooled data from 14 studies between 1998 and 2009 comprising 20 871 children (aged 4-18 years) from the International Children’s Accelerometry Database. Time spent in MVPA and sedentary time were measured using accelerometry after reanalyzing raw data. The independent associations between time in MVPA and sedentary time, with outcomes, were examined using meta-analysis. Participants were stratified by tertiles of MVPA and sedentary time.

MAIN OUTCOME MEASURES: Waist circumference, systolic blood pressure, fasting triglycerides, high-density lipoprotein cholesterol, and insulin.

RESULTS:Times (mean [SD] min/d) accumulated by children in MVPA and being sedentary were 30 (21) and 354 (96), respectively. Time in MVPA was significantly associated with all cardiometabolic outcomes independent of sex, age, monitor wear time, time spent sedentary, and waist circumference (when not the outcome). Sedentary time was not associated with any outcome independent of time in MVPA. In the combined analyses, higher levels of MVPA were associated with better cardiometabolic risk factors across tertiles of sedentary time. The differences in outcomes between higher and lower MVPA were greater with lower sedentary time. Mean differences in waist circumference between the bottom and top tertiles of MVPA were 5.6 cm (95% CI, 4.8-6.4 cm) for high sedentary time and 3.6 cm (95% CI, 2.8-4.3 cm) for low sedentary time. Mean differences in systolic blood pressure for high and low sedentary time were 0.7 mm Hg (95% CI, -0.07 to 1.6) and 2.5 mm Hg (95% CI, 1.7-3.3), and for high-density lipoprotein cholesterol, differences were -2.6 mg/dL (95% CI, -1.4 to -3.9) and -4.5 mg/dL (95% CI, -3.3 to -5.6), respectively. Geometric mean differences for insulin and triglycerides showed similar variation. Those in the top tertile of MVPA accumulated more than 35 minutes per day in this intensity level compared with fewer than 18 minutes per day for those in the bottom tertile. In prospective analyses (N = 6413 at 2.1 years’ follow-up), MVPA and sedentary time were not associated with waist circumference at follow-up, but a higher waist circumference at baseline was associated with higher amounts of sedentary time at follow-up.

CONCLUSION:Higher MVPA time by children and adolescents was associated with better cardiometabolic risk factors regardless of the amount of sedentary time.

The May 16 issue of JAMA contains further discussion of this important study.  Drs JP Chaput, Ian Janssen, and John Spence write:

Although the authors studied 20 871 children and adolescents and measured sedentary time in an objective way, we believe it is premature to conclude that sedentary time is not associated with adverse cardiometabolic health outcomesin children.

First, different types of sedentary behavior may have different metabolic effects and future studies should therefore investigate specific sedentary behaviors and not only the total accumulated time spent sedentary.

…

Second, though the cut point used to define sedentary behavior (100 counts/min on an accelerometer) provides a useful estimate of sitting time, standing still time may also be included as sedentary time.

…

Third, it is surprising that children with lower levels of sedentary time combined with lower levels of MVPA had the worst cardiometabolic outcomes. This group of children moves around a lot but at a low intensity.

Finally, food intake was not measured in this study and should be included in future research because of the strong link between poor dietary habits and cardiometabolic health and also because screen-time sedentary behavior has been shown to increase caloric intake in the absence of hunger

Drs Ekelund and colleagues replied to these concerns:

Dr Chaput and colleagues argue that it is premature to conclude that sedentary time is not associated with
cardiometabolic health outcomes in children. Our study concluded that “higher levels of time in MVPA appear to be associated with better cardiometabolic risk factors regardless of the amount of time spent sedentary in youth.” Our conclusion was strongly supported by the data, but we do not dismiss a potential role of specific sedentary behaviors in relation to cardiometabolic risk.

…

We only examined the associations with total sedentary time. Specific sedentary behaviors, such as TV viewing, may have different associations with cardiometabolic health outcomes. We stated that: “decreasing TV time in youth may still be an important public health goal as TV viewing may be associated with other unhealthy behaviors such as snacking and soft drink consumption. Further TV viewing is also associated with exposure to advertisements that often promote unhealthy dietary habits.”

In their conclusion, Drs Ekelund and colleagues suggest that both groups have reached a common conclusion:

Finally, Chaput et al state that “the take-home message should be to increase children’s participation in MVPA and reduce their screen-related sedentary time”; this is exactly what we proposed in our article.

The full article and the letters are available through the JAMA website.

Sedentary behaviour has been added to The Source, a site which provides introductory sex- and gender-based analyses (SGBA) on prominent topics in women’s health, as well as links to both local and international data sources.  Their article examines issues related to sex, gender, diversity and equity in relation to current sedentary behaviour research, as well as links to original data sources.

Their article ends with the following critique:

The relationships between sedentary behaviour and morbidity and mortality have not received as much research and policy attention as the relationship between physical activity, morbidity, and mortality. Most studies to date include only a limited selection of sedentary behaviours, such as watching television and computer games; involvement in these activities may vary by sex, income, and neighbourhood. Measuring sedentary behaviour is a challenge as these behaviours are often engaged in sporadically throughout the day and may be harder to recall than scheduled physical activities. Self-reports, a common measure of both physical activity and sedentary behaviour, may therefore not be a reliable measure of sedentary behaviour [3,6]. Further research using tools such as accelerometers or inclinometers is needed.

The full article is available for free via The Source.

People who drive long distances to work are more likely to be overweight and have poorer fitness levels than people who live closer to their jobs, a US study said Tuesday.

The study in the American Journal of Preventive Medicine was based on data from nearly 4,300 people in Texas near the major metropolitan hubs of Dallas-Fort Worth — one of the top five most congested areas in the United States — and nearby Austin.

People who drove longer distances to work were found generally to have larger waist circumferences, lower cardiovascular fitness levels, higher blood pressure and higher body-mass index.

The full article is available at Yahoo! News, and the pdf of the AJPM article is available for free here.  Hat tip to Rachel Laxer for locating the pdf!

Earlier today, the Sedentary Behaviour Research Network published an updated definition of the terms “sedentary” and “sedentary behaviour” in French and English in the journals Applied Physiology, Nutrition and Metabolism and Movement & Sport Sciences – Science & Motricité.  

The letter was created in response to confusion regarding the usage of the above terms in the published literature, and was signed by 52 individual SBRN members, including many of the most prominent researchers in the field.  It takes into account several factors including energy expenditure, posture, and whether or not a person is awake.

Thanks to the many individuals who contributed to the drafting and revising of the letter, and to Drs Gilles Thoni and Jean-Philippe Chaput for translating the letter into French.

Here is the definition of sedentary behaviour, as proposed by the SBRN membership:

We suggest that journals formally define sedentary behaviour as any waking behaviour characterized by an energy expenditure ≤1.5 METs while in a sitting or reclining posture. In contrast, we suggest that authors use the term “inactive” to describe those who are performing insufficient amounts of MVPA (i.e., not meeting specified physical activity guidelines).

Nous suggérons que les revues définissent de façon formelle le comportement sédentaire comme une situation d’éveil caractérisée par une dépense énergétique ≤1,5 METs en position assise ou allongée. En revanche, nous suggérons que les auteurs utilisent le terme « inactif » pour décrire les individus ayant un niveau insuffisant d’activité physique d’intensité modérée à intense (MVPA), c’est-à-dire, n’atteignant pas le seuil d’activité physique recommandé.

You can also access the full letter at the following links: English Letter / French Letter.

We are encouraging organizations working in this area to adopt this new common definition. In fact, the definition has already been endorsed by the Canadian Society for Exercise Physiology and La Société Française des Professionnels en Activités Physiques Adaptées.  Please cite the letter when defining sedentary behaviour in your papers, and please distribute it to other individuals who may find it useful.  Finally, please refer people to this definition when acting as a peer reviewer.

The definition can be cited as:

Studies of daily movement patterns, though, show that your typical modern exerciser, even someone who runs, subsequently sits for hours afterward, often moving less over all than on days when he or she does not work out.

The health consequences are swift, pervasive and punishing. In a noteworthy recent experiment conducted by scientists at the University of Massachusetts and other institutions, a group of healthy young men donned a clunky platform shoe with a 4-inch heel on their right foot, leaving the left leg to dangle above the ground. For two days, the men hopped about using crutches (and presumably gained some respect for those people who regularly toddle about in platform heels). Each man’s left leg never touched the ground. Its muscles didn’t contract. It was fully sedentary.

After two days, the scientists biopsied muscles in both legs and found multiple genes now being expressed differently in each man’s two legs. Gene activity in the left leg suggested that DNA repair mechanisms had been disrupted, insulin response was dropping, oxidative stress was rising, and metabolic activity within individual muscle cells was slowing after only 48 hours of inactivity.

The full article is available through the New York Times website.

In the coming months we will be having informal SBRN meetups at conferences including ISBNPA (Austin, USA), ACSM (San Francisco, USA) and ICDAM (Rome, Italy).  We also have an official SBRN publication In Press in 2 journals urging the adoption of a consistent definition of sedentary behaviour (signed by 53 separate SBRN members!), which will be unveiled as soon as possible.  For more info on how to get involved in these initiatives be sure to look for emails from the SBRN list serve in your inbox.

Finally, the website has become increasingly popular since going online in September of 2011.  The site has received just under 5000 visits, and now ranks among the top Google results for searches related to sedentary behaviour (using both American and Commonwealth spelling).

If anyone else has ideas for SBRN initiatives or meetups feel free to contact us through the website or through the SBRN member list serve.

The impact of sitting and energy imbalance on appetite and appetite-regulating hormones (acylated ghrelin and leptin) was assessed in response to 1 day of sitting, with and without changes in energy intake. Fourteen men and women completed each of three 24-h conditions: high energy expenditure (standing) with energy balance (STAND), low energy expenditure (sitting) with energy surplus (SIT), and sitting with energy balance (SIT-BAL). Ghrelin, leptin, and appetite were measured in the fasted state and following a standardized meal. In the fasted state, there were no differences among conditions. Following the meal, ghrelin was lower in SIT than in STAND, with no change in appetite. When intake was reduced (SIT-BAL), the decrease in ghrelin when sitting was attenuated, hunger increased, and fullness decreased. SIT led to lower ghrelin concentrations in the men, whereas in the women, leptin increased. SIT-BAL led to an increase in ghrelin in the men but attenuated the leptin response, reduced ghrelin, increased hunger, and decreased fullness in the women. Because a dramatic reduction in energy expenditure was not accompanied by reduced appetite, prolonged sitting may promote excess energy intake, leading to weight gain in both men and women.

The full text of the article is available through the Applied Physiology, Nutrition and Metabolism website.

A group  of researchers based in Britain are attempting to create a taxonomy of terms related to sedentary behaviour.

From the SIT website:

SIT is a open science project setup to develop a common taxonomy (naming and classification system) of sedentary behaviours through a formal consensus process taking into account the opinion of experts and of the general public.

Aim: To develop a common taxonomy of sedentary behaviours in order to

- Facilitate systematic and standardised investigation and analysis
- Enable systematic and standardised reporting
- Facilitate comparison and metanalysis
- Facilitate development of measurement tools sensors and outcome measures.

They have contacted 200 researchers in the area of sedentary behaviour (many of them SBRN members), and have received an excellent response so far.  If you are interested in learning more about SIT or joining in their efforts, please visit their website at http://sedentarybehaviourclassification.net/.

The full-text of today’s study is available for free through the website of Applied Physiology, Nutrition and Metabolism.  The article can be accessed here.

Introduction

Sedentary behaviour among children in the early years (defined in the paper as aged 0-4 years) is gaining increasing attention. Accumulating evidence suggests that the sedentary behaviour habits formed in this age group, in particular screen-based sedentary behaviour habits, have potential short- and long-term health implications. This evidence combined with the recognized public health importance of growth and development during this time period led the Canadian Society for Exercise Physiology to develop the first Canadian Sedentary Behaviour Guidelines for the Early Years (aged 0-4 years). These guidelines addressed a need established by health care professionals, child care providers, and other stakeholders in Canada regarding guidance on sedentary behaviour in the early years. The purpose of this paper was to outline the process and outcomes for the development of these new national guidelines, which have just been released.

What was done?

The paper outlines three main steps that were involved in developing the guidelines. First, a systematic review was conducted to identify the best available evidence regarding sedentary behaviour and six health outcomes (adiposity, bone health, motor development, psychosocial health, cognitive development, cardio-metabolic health) among infants (<1 year), toddlers (1-2 years), and preschoolers (3-4 years). The evidence from the systematic review was assessed using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system. Second, a consensus meeting was held in December 2011with the Guideline Development and Research Committee to discuss the evidence from the systematic review and draft the guidelines. Third, in addition to the stakeholder input that was acquired throughout the process, a stakeholder consultation was conducted through an on-line survey to obtain feedback on the draft guidelines. All components were guided by the Appraisal of Guidelines for Research Evaluation (AGREE) II instrument, which assessed the scientific rigour and transparency of the entire guideline development process.

What was found?

In terms of the systematic review, the detailed results are published in a separate paper. In summary, 23 papers were included in the review that examined the effects of television viewing on adiposity, cognitive development, or psychosocial health. Overall, there was low to high quality evidence across the infant, toddler, and preschool age groups to suggest that television viewing is positively associated with adiposity and negatively associated with cognitive development and psychosocial health. However, consistent dose-response evidence was lacking; therefore, expert consensus, international harmonization, and stakeholder input was used to inform the guidelines. In terms of the stakeholder consultation, 925 stakeholders completed the survey and 92% completely agreed or agreed with the guideline documents. Furthermore, the 212 additional comments provided by the stakeholders were used to make revisions to the final guideline documents.

What are the guidelines?

“For healthy growth and development, caregivers should minimize the time infants (aged<1 year), toddlers (aged 1-2 years), and preschoolers (aged 3-4 years) spend being sedentary during waking hours. This includes prolonged sitting or being restrained (e.g., stroller, high chair) for more than 1 h at a time. For those under 2 years, screen time (e.g., TV, computer, electronic games) is not recommended. For children 2-4years, screen time should be limited to under 1 hr per day; less is better.”

The guidelines paper can be found at the link below, while information sheets can be accessed at www.csep.ca/guidelines.

Reference

Tremblay MS, LeBlanc AG, Carson V, Choquette L, Connor Gorber S, Dillman C, Duggan M, Gordon MJ, Hicks A, Janssen I, Kho ME, Latimer-Cheung AE, LeBlanc C, Murumets K, Okely AD, Reilly JJ, Stearns JA, Timmons BW, & Spence JC. Canadian Sedentary Behaviour Guidelines for the Early Years (aged 0-4 years). Appl. Physiol. Nutr. Metab. 2012.

Valerie Carson

About the author: Valerie Carson is in the final year of her PhD in the School of Kinesiology and Health Studies at Queen’s University. Her current research focuses on sedentary behaviour and health in young people.

Canadian adults are now spending about three-quarters of their time sedentary, according to Mark Tremblay, director of the Healthy Active Living and Obesity Research Group (HALO) at the CHEO Research Institute in Ottawa. A growing body of research suggests that too much sedentary time carries risks—even for those who diligently exercise. In September, Tremblay’s group launched the Sedentary Behaviour Research Network (SBRN) to study the impact of all the time we spend inactive, the dangers of which we’re only starting to understand. Jean-Philippe Chaput, junior research chair at HALO, puts it bluntly: “Independent of physical activity, sitting too much is killing us.”

…

The researchers who study sedentary behaviour practise what they preach: when contacted by Maclean’s, each conducted the interview while standing up.

The complete article can be accessed for free on the Maclean’s website.