Effects of breaking up sitting on adolescents' postprandial glucose after consuming meals varying in energy: a cross-over randomised trial

Cross-sectional comparison of the association between three different insulin resistance surrogates and frailty: NHANES 1999-2018

Background

The correlation between various insulin resistance surrogates and frailty remains under investigation in the scientific community.

Methods

Data from NHANES (1999-2018) were used. We utilized weighted binary logistic regression, trend tests, RCS analysis, and subgroup analysis to comprehensively assess the link between METS-IR, HOMA-IR, and TyG, and frailty risk.

Results

The results revealed a significant positive association between high levels of METS-IR, HOMA-IR, and TyG with the risk of frailty in all models. Notably, in model 4, the highest quintile of METS-IR showed the strongest link (OR: 2.960, 95% CI: 2.219-3.949), with HOMA-IR (OR: 2.522, 95% CI: 1.927-3.301) following closely behind. Trend tests revealed a positive trend between METS-IR, HOMA-IR, and TyG with the risk of frailty (P for trend < 0.05). RCS analysis showed a linear relationship between METS-IR and the risk of frailty (P for nonlinearity > 0.05). In contrast, HOMA-IR and TyG exhibited a U-shaped nonlinear relationship (P for nonlinearity < 0.05).

Conclusion

The research identified a linear association between METS-IR and frailty risk, whereas HOMA-IR and TyG displayed a U-shaped, nonlinear relationship pattern with the risk of frailty. Among the varying levels examined, the linkage between METS-IR and frailty was most pronounced in the top quintile.

Enhancing cardiometabolic health through physical activity and breakfast manipulations in children and adolescents: good for humans, good for the planet

The human health benefits of cardiometabolic disease prevention can be accompanied by planetary co-benefits. Focusing efforts towards young people, including children and adolescents, is conducive to disease prevention. In the context of cardiometabolic disease prevention, this review paper critically summarises the available literature on the acute cardiometabolic responses to physical activity and breakfast manipulations among young people. Given the seriousness of global climate change, which will disproportionally affect our younger generations, this review paper offers new insights into the inherent interactions between child-adolescent behaviour and cardiometabolic health from an environmental sustainability perspective to aid climate change mitigation efforts, including exploring future research avenues. A growing evidence base suggests acute moderate- to high-intensity exercise bouts can attenuate postprandial plasma glucose, insulin and triacylglycerol concentrations for up to 24-48 h in young people. Whether accumulating physical activity throughout the day with short, frequent bouts promotes cardiometabolic risk marker attenuations is unclear. Breakfast consumption may enhance free-living physical activity and reduce glycaemic responses to subsequent meals for a possible additive impact. If repeated habitually, attenuations in these cardiometabolic risk factors would be conducive to disease prevention, reducing the greenhouse gas emissions associated with disease diagnosis and treatment. To progress current understanding with high public health and planetary relevance, research among samples of 'at risk' young people that span cellular-level responses to ecologically valid settings and address human and planetary health co-benefits is needed. Indeed, certain physical activity opportunities, such as active travel to school, offer important direct co-benefits to humans and planetary health.

Performance of the FreeStyle Libre Flash Glucose Monitoring System during an Oral Glucose Tolerance Test and Exercise in Healthy Adolescents

This study's aim was to assess FreeStyle Libre Flash glucose monitoring (FGM) performance during an oral glucose tolerance test (OGTT) and treadmill exercise in healthy adolescents. This should advance the feasibility and utility of user-friendly technologies for metabolic assessments in adolescents. Seventeen healthy adolescents (nine girls aged 12.8 ± 0.9 years) performed an OGTT and submaximal and maximal treadmill exercise tests in a laboratory setting. The scanned interstitial fluid glucose concentration ([ISFG]) obtained by FGM was compared against finger-prick capillary plasma glucose concentration ([CPG]) at 0 (pre-OGTT), -15, -30, -60, -120 min post-OGTT, pre-, mid-, post- submaximal exercise, and pre- and post- maximal exercise. Overall mean absolute relative difference (MARD) was 13.1 ± 8.5%, and 68% (n = 113) of the paired glucose data met the ISO 15197:2013 criteria. For clinical accuracy, 84% and 16% of FGM readings were within zones A and B in the Consensus Error Grid (CEG), respectively, which met the ISO 15197:2013 criteria of having at least 99% of results within these zones. Scanned [ISFG] were statistically lower than [CPG] at 15 (-1.16 mmol∙L^-1, p < 0.001) and 30 min (-0.74 mmol∙L^-1, p = 0.041) post-OGTT. Yet, post-OGTT glycaemic responses assessed by total and incremental areas under the curve (AUCs) were not significantly different, with trivial to small effect sizes (p ≥ 0.084, d = 0.14-0.45). Further, [ISFGs] were not different from [CPGs] during submaximal and maximal exercise tests (interaction p ≥ 0.614). FGM can be a feasible alternative to reflect postprandial glycaemia (AUCs) in healthy adolescents who may not endure repeated finger pricks.

Effects of interrupting daily sedentary behavior on children's glucose metabolism: A 6-day randomized controlled trial

BACKGROUND

Metabolic disease risk in youth is influenced by sedentary behaviors. Acute in-lab studies show that, during a single day, interrupting a sedentary period with short bouts of physical activity improves glucometabolic outcomes.

OBJECTIVE

To determine if acutely improved glucose metabolism persists after multi-day interruptions of sitting with walking brief bouts. We hypothesized that children who underwent interrupting sitting on multiple days would demonstrate lower insulin area under the curve during an oral glucose tolerance test compared to uninterrupted sitting.

METHODS

Healthy, normoglycemic children (N = 109) ages 7-11 years were randomized to one of two conditions: Control (3 h of daily Uninterrupted Sitting) or Interrupted Sitting (3-min of moderate-intensity walking every 30 min for 3 h daily); with dietary intake controlled through provision of foodstuffs for the entire experiment. Participants attended six consecutive daily visits at a research ambulatory unit. The primary outcome was insulin area under the curve during the oral glucose tolerance test on day 6 during interrupted or uninterrupted sitting; secondary outcomes included glucose and c-peptide area under the curve, energy intake at a buffet meal on day 6, and free-living activity.

RESULTS

Among 93 children (42 uninterrupted sitting, 51 interrupted sitting), daily interrupted sitting resulted in 21% lower insulin (β = 0.102 CI:0.032-0.172, p = 0.005) and a 10% lower C-peptide (β = 0.043, CI:0.001-0.084, p = 0.045) area under the curve. Matsuda and Glucose Effectiveness Indices were also improved (p's < 0.05). There were no group differences in energy intake or expenditure.

CONCLUSIONS

Sustained behavioral change by interrupting sedentary behaviors is a promising intervention strategy for improving metabolic risk in children.

Breaking Sitting Time with Physical Activity Increases Energy Expenditure but Does Not Alter Postprandial Metabolism in Girls

PURPOSE

Young people spend a substantial proportion of their time at school sedentary; therefore, this setting represents an important target for interventions aimed at displacing sedentary time with physical activity. This study aimed to examine the postprandial metabolic effects of breaking sedentary time by accumulating walking and repeated bouts of nonambulatory standing during simulated school days in inactive adolescent girls.

METHODS

Seventeen girls (mean ± SD = 12.8 ± 0.4 yr) completed two 3-d experimental conditions. On days 1 and 2 of the standing + walking (STD-WLK) experimental trial, participants interrupted sedentary time by completing 4 × 10 min bouts of self-paced walking and accumulated 18 × 5 min standing bouts during each simulated school day. On day 3 of STD-WLK, participants attended school as normal with no additional physical activity or standing prescribed. On all 3 d of the control condition (CON), participants attended school as normal with no physical activity intervention. On days 2 and 3 of both STD-WLK and CON, a baseline capillary blood sample was provided to determine fasting [TAG] and [glucose]. Participants then consumed a standardized breakfast (0 h) and lunch (4.7 h), and blood samples were provided postprandially at 2.7, 5.3, and 7.3 h for [TAG] and [glucose].

RESULTS

Energy expenditure was 28% (95% confidence interval = 8% to 52%) higher during school hours on day 1 and day 2 during STD-WLK compared with CON (2171 vs 1693 kJ; effect size = 0.89, P = 0.008). However, no reduction of fasting or postprandial [TAG] or [glucose] was observed on day 2 or day 3 ( P ≥ 0.245).

CONCLUSIONS

Two consecutive days of breaking prolonged sitting with self-paced walking and intermittent standing had no meaningful effect on postprandial metabolism in adolescent girls.

Does light-intensity physical activity moderate the relationship between sitting time and adiposity markers in adolescents?

BACKGROUND

While the relationship between sedentary time and adiposity markers may be independent of moderate-to-vigorous intensity physical activity (MVPA) among adolescents, little is known about the role of light-intensity physical activity (LIPA) in this relationship. The aim of this cross-sectional study was to examine whether device-measured LIPA and MVPA moderate the associations between objectively measured sitting time and adiposity markers (body mass index (BMI)) and waist circumference (WC)) among adolescents.

METHODS

This study included accelerometer and inclinometer data obtained from 219 adolescents (age = 14.9 ± 1.6 years, mean ± SD), collected during 2014 and 2015 in Melbourne, Australia. ActiGraph GT3X accelerometers were used to determine time spent in total-LIPA (101 counts/min to 3.99 metabolic equivalents (METs)) was dichotomized into low-LIPA (101-799 counts/min) and high LIPA (800 counts/min to 3.99 METs), and MVPA (≥ 4 METs). The average time spent sitting was obtained from activPAL inclinometers. Anthropometric measures were assessed by trained staff. Interactions between sitting and total-LIPA, low-LIPA, high-LIPA, and MVPA on BMI z-score (zBMI) and WC z-score (zWC), respectively, were examined using linear regression, adjusting for age and sex; and moderation by total-LIPA, low-LIPA, high-LIPA, and MVPA were examined by adding interaction terms. Significant interaction effects were probed by comparing associations at the mean and at 1 SD below and above the mean.

RESULTS

Total-LIPA significantly moderated the association between sitting time and zBMI, and low-LIPA significantly moderated the association between sitting time and zBMI and zWC. No other associations were found for total-LIPA, high-LIPA, or MVPA. Specifically, at high levels of total-LIPA (+1 SD), there is a negative association between sitting time and zBMI. In addition, at high levels of low-LIPA (+1 SD), there is a negative association between sitting time and zBMI and zWC.

CONCLUSION

Associations between sitting and adiposity depended on time spent in total-LIPA and low-LIPA, but not high-LIPA or MVPA. Results suggest that increasing time spent in LIPA may provide protection from the deleterious effects of sitting on adiposity markers among adolescents. Experimental evidence is needed to support these conclusions.

Diet and Physical Activity as Determinants of Continuously Measured Glucose Levels in Persons at High Risk of Type 2 Diabetes

We examined how dietary and physical activity behaviors influence fluctuations in blood glucose levels over a seven-day period in people at high risk for diabetes. Twenty-eight participants underwent a mixed meal tolerance test to assess glucose homeostasis at baseline. Subsequently, they wore an accelerometer to assess movement behaviors, recorded their dietary intakes through a mobile phone application, and wore a flash glucose monitoring device that measured glucose levels every 15 min for seven days. Generalized estimating equation models were used to assess the associations of metabolic and lifestyle risk factors with glycemic variability. Higher BMI, amount of body fat, and selected markers of hyperglycemia and insulin resistance from the meal tolerance test were associated with higher mean glucose levels during the seven days. Moderate- to vigorous-intensity physical activity and polyunsaturated fat intake were independently associated with less variation in glucose levels (CV%). Higher protein and polyunsaturated fatty acid intakes were associated with more time-in-range. In contrast, higher carbohydrate intake was associated with less time-in-range. Our findings suggest that dietary composition (a higher intake of polyunsaturated fat and protein and lower intake of carbohydrates) and moderate-to-vigorous physical activity may reduce fluctuations in glucose levels in persons at high risk of diabetes.

The influence of sex and maturation on carotid and vertebral artery hemodynamics and associations with free-living (in)activity in 6-17-year-olds

We explored the influence of sex and maturation on resting cervical artery hemodynamics (common carotid artery, CCA; internal carotid artery, ICA; and vertebral artery, VA), free-living physical activity, and sedentary behavior in children 6-17 yr of age. In addition, we investigated the relationship between physical activity, sedentary behavior, and cervical artery hemodynamics. Seventy-eight children and adolescents, girls (n = 42; mean age, 11.4 ± 2.5 yr) and boys (n = 36; mean age, 11.0 ± 2.6 yr), completed anthropometric measures, duplex ultrasound assessment of the cervical arteries, and wore an activPAL accelerometer to assess physical activity (indexed by steps/day) and sedentary behavior for 7 days. The ICA and VA diameters were similar between prepubertal and pubertal groups, as was volumetric blood flow (Q); however, the CCA diameter was significantly larger in the pubertal group (P < 0.05). Boys were found to have larger diameters in all cervical arteries than girls, as well as higher Q_CCA, Q_ICA, and global cerebral blood flow (P < 0.05). The pubertal group was more sedentary (100 min/day more; P < 0.05) and took 3,500 fewer steps/day than the prepubertal group (P < 0.05). Shear rate (SR) and Q of the cervical arteries showed no relationship to physical activity or prolonged bouts of sedentary behavior; however, a significant negative relationship was apparent between total sedentary time and internal carotid artery shear rate (ICA_SR) after covarying for steps/day and maturation (P < 0.05). These findings provide novel insight into the potential influence sedentary behavior may have on cerebrovascular blood flow in healthy girls and boys.NEW & NOTEWORTHY Cerebral blood flow is known to change with age; however, assessing these age-related changes is complex and requires consideration of pubertal status. This, to our knowledge, is the first study to investigate the influence of sex and maturation on resting cervical artery hemodynamics and subsequently explore associations with physical activity and sedentary behavior in healthy children and adolescents. Our findings suggest that habitual sedentary behavior may influence cervical artery hemodynamics in youth, independent of physical activity, maturation, and sex.

Acute Effects of Frequent Light-Intensity Standing-Based Exercises That Interrupt 8 Hours of Prolonged Sitting on Postprandial Glucose in Stroke Survivors: A Dose-Escalation Trial

BACKGROUND

Interrupting prolonged sitting can attenuate postprandial glucose responses in overweight adults. The dose-response effect in stroke survivors is unknown. The authors investigated the effects of interrupting 8 hours of prolonged sitting with increasingly frequent bouts of light-intensity standing-based exercises on the postprandial glucose response in stroke survivors.

METHODS

Within-participant, laboratory-based, dose-escalation trial. Participants completed three 8-hour conditions: prolonged sitting and 2 experimental conditions. Experimental conditions involved light-intensity standing-based exercises of increasing frequency (2 × 5 min to 6 × 5 min bouts). Postprandial glucose is reported.

RESULTS

Twenty-nine stroke survivors (aged 66 y) participated. Interrupting 8 hours of prolonged sitting with light-intensity standing-based exercises every 90 minutes significantly decreased postprandial glucose (positive incremental area under the curve; -1.1 mmol/L·7 h; 95% confidence interval, -2.0 to -0.1). In the morning (08:00-11:00), postprandial glucose decreased during the 4 × 5 minutes and 6 × 5 minutes conditions (positive incremental area under the curve; -0.8 mmol/L·3 h; 95% confidence interval, -1.3 to -0.3 and -0.8 mmol/L·3 h; 95% confidence interval, -1.5 to -0.2, respectively) compared with prolonged sitting.

CONCLUSION

Interrupting 8 hours of prolonged sitting at least every 90 minutes with light-intensity standing-based exercises attenuates postprandial glucose in stroke survivors. During the morning, postprandial glucose is attenuated when sitting is interrupted every 60 and 90 minutes.

Volume and accumulation patterns of physical activity and sedentary time: longitudinal changes and tracking from early to late childhood

BACKGROUND

Physical activity (PA) decreases and sedentary time (SED) increases across childhood, with both behaviours tracking. However, no studies have examined how accumulation patterns of PA and SED (i.e., prolonged bouts, frequency of breaks in sedentary time) change and track over time. The aim of this study was to investigate longitudinal changes in and tracking of total volume and accumulation patterns of SED, light-intensity PA (LPA), moderate-intensity PA (MPA), vigorous-intensity PA (VPA) among boys and girls.

METHODS

In 2008/09 (T1), children in HAPPY (3-5y; n = 758) in Melbourne, Australia wore ActiGraph GT1M accelerometers to objectively assess SED, LPA, MPA and VPA. This was repeated at age 6-8y (T2; n = 473) and 9-11y (T3; n = 478). Ten pattern variables were computed: bouts of ≥ 5-, ≥ 10-, ≥ 15- and ≥ 20-min for SED, ≥ 1- and ≥ 5-min for LPA, ≥ 1-min for MPA, ≥ 1- and ≥ 5-min for VPA, and breaks in SED (interruptions of > 25 counts 15 s^- 1). Longitudinal mixed models examined changes from T1-3, controlling for T1 age. Generalized estimating equations assessed tracking over the three time points, controlling for T1 age and time between measurements. Analyses were stratified by sex.

RESULTS

Total volume and bouts of SED and SED breaks increased, while total volume and bouts of LPA decreased for both sexes. There was a small decrease in total volume of MPA for girls, but time spent in ≥ 1-min bouts increased for both sexes. Total volume of VPA increased for both sexes, with time spent in ≥ 1-min bouts increasing for boys only. All volume and pattern variables tracked moderately for boys, except for all SED bouts ≥ 15-min, LPA bouts ≥ 5-min and MPA bouts ≥ 1-min (which tracked weakly). For girls, total SED and SED bouts ≥ 1-min tracked strongly, total volume of LPA, MPA and VPA, ≥ 5- and ≥ 10-min SED bouts, and ≥ 1-min LPA and MPA bouts tracked moderately, and SED breaks, all SED bouts ≥ 15 min, LPA bouts ≥ 5 min and all VPA bouts tracked weakly.

CONCLUSIONS

Patterns of SED and PA change from early to late childhood; with the exception of SED breaks and VPA, changes were detrimental. Total volumes and short bouts tended to track more strongly than longer bouts. Interventions to prevent declines in PA and increases in SED are important from early in life.

Moving More and Sitting Less as Healthy Lifestyle Behaviors are Protective Factors for Insomnia, Depression, and Anxiety Among Adolescents During the COVID-19 Pandemic

PURPOSE

This study aimed to investigate associations of physical activity time (PAT) and sitting time (ST) independently and jointly with insomnia, depressive and anxiety symptoms among Chinese adolescents in the context of COVID-19.

METHODS

A cross-sectional study including 965 adolescents (mean age = 15.26, SD = 0.46) was conducted in May 2020. PAT, ST and the symptoms of insomnia, depression and anxiety were assessed with the International Physical Activity Questionnaire Short Form, the Youth Self-Rating Insomnia Scales, the 9-item Patient Health Questionnaire and the Generalized Anxiety Disorder scale via an online survey platform. Logistic regression was used to analyze the association between COVID-19-related fear, PAT, ST and combinations of PAT and ST with insomnia, depressive and anxiety symptoms.

RESULTS

COVID-19-related fear was associated with higher odds of insomnia, depressive and anxiety symptoms. PAT was associated with lower odds of insomnia and depressive symptoms, while ST was associated with higher odds of these three symptoms. After combining PAT and ST, the group with both low PAT and high ST was set as the referent. For insomnia, groups with low ST reported significantly lower odds of symptoms. For depression, groups with high PAT and/or low ST reported lower odds of symptoms. Regarding anxiety, only the group with both high PAT and low ST reported lower odds of symptoms. Generally, group with both high PAT and low ST reported lower odds of the three symptoms than the referent.

CONCLUSION

COVID-19-related fear was a risk factor for developing insomnia, depressive and anxiety symptoms among Chinese adolescents. Fortunately, moving more and sitting less were good for sleep and mental health in Chinese adolescents during the pandemic. Educators should help adolescents to be more physically active in their daily life in the primary prevention of adolescent insomnia, depression and anxiety.

Impact of prolonged sitting and physical activity breaks on cognitive performance, perceivable benefits, and cardiometabolic health in overweight/obese adults: The role of meal composition

BACKGROUND & AIMS

Physical activity (PA) breaks may effectively attenuate the detrimental impact of prolonged sitting on acute cognitive performance, perceivable benefits (e.g. mood), vascular function, and metabolic health. To date, the impact of meal composition on the effects of sedentary behavior and/or PA breaks on health has been scarcely studied. Therefore, our aim was to investigate whether meal composition alters how sedentary behavior and PA breaks affect these acute health outcomes.

METHODS

A total of 24 overweight and obese, sedentary adults completed four conditions in randomized order in a cross-over design: [a] high-protein, low-fat breakfast (HPLF) + 4hrs uninterrupted sitting (SIT), [b] HPLF + 4hrs interrupted sitting (ACT; 5-min cycling every 30 min), [c] Western breakfast (WEST; higher in fats/simple sugars, lower in protein/fiber) + SIT, [d] WEST + ACT. WEST and HPLF were isocaloric. Linear mixed models were used to examine changes in cognitive performance (Test of Attentional Performance), perceivable benefits (Likert-scales, Profile of Mood States questionnaire), vascular health (carotid artery reactivity, blood pressure), and metabolic health (post-breakfast glucose, insulin, lipids).

RESULTS

Independent of meal composition, we did not observe any effect of PA breaks on cognitive performance, vascular health and post-breakfast lipid responses. PA breaks delayed post-breakfast mood and vigor decrements, as well as increases in fatigue and sleepiness (all p < 0.05), but effects were independent of meal composition (p > 0.05). WEST resulted in higher post-breakfast glucose levels compared to HPLF (p < 0.05), while PA breaks did not impact this response (p > 0.05). PA breaks reduced post-breakfast insulin (p < 0.05), which did not differ between meals (p > 0.05).

CONCLUSIONS

The acute impact of PA breaks and/or prolonged sitting on cognitive performance, perceivable benefits, and vascular and metabolic health was not altered by the composition of a single meal in overweight/obese, sedentary adults. Possibly, breaking up prolonged sitting, rather than meal composition, is a more potent strategy to impact acute health outcomes, such as perceivable benefits and insulin levels.

Physical Activity, Sedentary Behaviour and Sleep, and Their Association with BMI in a Sample of Adolescent Females in New Zealand

Despite activity guidelines moving towards a 24-h focus, we have a poor understanding of the 24-h activity patterns of adolescents. Therefore, this study aims to describe the 24-h activity patterns of a sample of adolescent females and investigate the association with body mass index (BMI). Adolescent females aged 15-18 years (n = 119) were recruited across 13 schools in 8 locations throughout New Zealand. Actigraph GT3X+ accelerometers were worn 24-h a day for seven days and the output was used to identify time spent in each 24-h component (sleep, sedentary, light-intensity physical activity and moderate-to-vigorous intensity physical activity). In a 24-h period, adolescent females spent approximately half their time sedentary, one third sleeping and the remainder in light-intensity physical activity (15%) and moderate-to-vigorous intensity physical activity (5%). Higher BMI z-scores were associated with 16 min more time spent in light-intensity physical activity. Additionally, those with higher BMI were less likely to meet the sleep and physical activity guidelines for this age group. Compliance with the moderate-to-vigorous intensity physical activity guidelines, sleep guidelines, or both, was low, especially in those classified as overweight or obese. The association between BMI and light activity warrants further investigation.

Interstitial glucose and subsequent affective and physical feeling states: A pilot study combining continuous glucose monitoring and ecological momentary assessment in adolescents

OBJECTIVE

Circulating glucose may relate to affective and physical feeling states reflective of emotional disorder symptoms. No prior studies have investigated within-day associations between glucose and subsequent affective and physical feeling states (positive affect, negative affect, and fatigue) as they occur naturally among healthy adolescents; this pilot study assessed these associations by combining data collected from ecological momentary assessment (EMA) and continuous glucose monitors (CGM).

METHODS

Participants (N = 15, mean age = 13.1[±1.0] years, 66.7% female, 40.0% Hispanic, 66.7% healthy weight) wore a CGM for 7-14 days. Simultaneously, participants reported on their current positive affect, negative affect, and fatigue randomly during specified windows up to 7 times daily via EMA. CGM-measured mean interstitial glucose was calculated during the time windows (mean minutes = 122.5[±47.3]) leading up to each EMA prompt. Multilevel models assessed within-subject (WS) associations between mean interstitial glucose since the previous EMA prompt and EMA-reported affective and physical feeling states at the current prompt.

RESULTS

Participants provided 532 interstitial glucose-matched EMA reports of affective and physical feeling states. During intervals when interstitial glucose was higher than one's usual, higher positive affect (WS β = 0.01, p < .0001, f² = 0.02) and lower fatigue (WS β = -0.01, p < .0001, f² = 0.09) were subsequently reported. Interstitial glucose was unrelated to negative affect (WS β = -0.002, p = .10, f² = 0.01). Associations were weakened, but remained significant following further adjustment for time of day.

CONCLUSIONS

Though effect sizes were small, within-person variations in interstitial glucose may relate to subsequent affective and physical feeling states among healthy youth. Investigations using similar methodologies in larger, more diverse samples are warranted.

Effects of Interrupting Prolonged Sitting with Physical Activity Breaks on Blood Glucose, Insulin and Triacylglycerol Measures: A Systematic Review and Meta-analysis

BACKGROUND

Physical activity (PA) breaks in sitting time might attenuate metabolic markers relevant to the prevention of type 2 diabetes.

OBJECTIVES

The primary aim of this paper was to systematically review and meta-analyse trials that compared the effects of breaking up prolonged sitting with bouts of PA throughout the day (INT) versus continuous sitting (SIT) on glucose, insulin and triacylglycerol (TAG) measures. A second aim was to compare the effects of INT versus continuous exercise (EX) on glucose, insulin and TAG measures.

METHODS

The review followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) recommendations. Eligibility criteria consisted of trials comparing INT vs. SIT or INT vs. one bout of EX before or after sitting, in participants aged 18 or above, who were classified as either metabolically healthy or impaired, but not with other major health conditions such as chronic obstructive pulmonary disease or peripheral arterial disease.

RESULTS

A total of 42 studies were included in the overall review, whereas a total of 37 studies were included in the meta-analysis. There was a standardised mean difference (SMD) of - 0.54 (95% CI - 0.70, - 0.37, p = 0.00001) in favour of INT compared to SIT for glucose. With respect to insulin, there was an SMD of - 0.56 (95% CI - 0.74, - 0.38, p = 0.00001) in favour of INT. For TAG, there was an SMD of - 0.26 (95% CI - 0.44, - 0.09, p = 0.002) in favour of INT. Body mass index (BMI) was associated with glucose responses (β = - 0.05, 95% CI - 0.09, - 0.01, p = 0.01), and insulin (β = - 0.05, 95% CI - 0.10, - 0.006, p = 0.03), but not TAG (β = 0.02, 95% CI - 0.02, 0.06, p = 0.37). When energy expenditure was matched, there was an SMD of - 0.26 (95% CI - 0.50, - 0.02, p = 0.03) in favour of INT for glucose, but no statistically significant SMDs for insulin, i.e. 0.35 (95% CI - 0.37, 1.07, p = 0.35), or TAG i.e. 0.08 (95% CI - 0.22, 0.37, p = 0.62). It is worth noting that there was possible publication bias for TAG outcomes when PA breaks were compared with sitting.

CONCLUSION

The use of PA breaks during sitting moderately attenuated post-prandial glucose, insulin, and TAG, with greater glycaemic attenuation in people with higher BMI. There was a statistically significant small advantage for PA breaks over continuous exercise for attenuating glucose measures when exercise protocols were energy matched, but no statistically significant differences for insulin and TAG. PROSPERO Registration: CRD42017080982.

PROSPERO REGISTRATION

CRD42017080982.

The effect of a split portion of flaxseed on 24-h blood glucose response

Purpose

Flaxseed can be effective at lowering and stabilising blood glucose responses. The aim of this study was to determine whether flaxseed could lower blood glucose response more effectively when consumed as a single portion of 30 g, or a split portion consumed three times per day (10 g flaxseed per portion).

Methods

The study was a randomised, repeated measures, cross-over design. Fifteen healthy participants consumed either (1) three flaxseed muffins containing a total of 30 g of flaxseed once in the morning, (2) three flaxseed muffins consumed at three different timepoints across the day (10 g flaxseed per muffin) or (3) three control muffins consumed at three different timepoints across the day (0 g flaxseed). The 24-h blood glucose response was measured using a continuous glucose monitor.

Results

The results of this study demonstrated that flaxseed muffins given three times a day were effective at lowering and maintaining blood glucose levels over 24 h, compared to the control muffins and that both flaxseed treatments resulting in a lower blood glucose iAUC during the night.

Conclusion

The results of this study indicated that adding flaxseed to a daily diet produced a lower glucose profile over 24 h in a free-living context compared to the control muffins.

Sedentary Behavior and Public Health: Integrating the Evidence and Identifying Potential Solutions

In developed and developing countries, social, economic, and environmental transitions have led to physical inactivity and large amounts of time spent sitting. Research is now unraveling the adverse public health consequences of too much sitting. We describe improvements in device-based measurement that are providing new insights into sedentary behavior and health. We consider the implications of research linking evidence from epidemiology and behavioral science with mechanistic insights into the underlying biology of sitting time. Such evidence has led to new sedentary behavior guidelines and initiatives. We highlight ways that this emerging knowledge base can inform public health strategy: First, we consider epidemiologic and experimental evidence on the health consequences of sedentary behavior; second, we describe solutions-focused research from initiatives in workplaces and schools. To inform a broad public health strategy, researchers need to pursue evidence-informed collaborations with occupational health, education, and other sectors.

Sedentary behavior patterns and adiposity in children: a study based on compositional data analysis

BACKGROUND

Between-person differences in sedentary patterns should be considered to understand the role of sedentary behavior (SB) in the development of childhood obesity. This study took a novel approach based on compositional data analysis to examine associations between SB patterns and adiposity and investigate differences in adiposity associated with time reallocation between time spent in sedentary bouts of different duration and physical activity.

METHODS

An analysis of cross-sectional data was performed in 425 children aged 7-12 years (58% girls). Waking behaviors were assessed using ActiGraph GT3X accelerometer for seven consecutive days. Multi-frequency bioimpedance measurement was used to determine adiposity. Compositional regression models with robust estimators were used to analyze associations between sedentary patterns and adiposity markers. To examine differences in adiposity associated with time reallocation, we used the compositional isotemporal substitution model.

RESULTS

Significantly higher fat mass percentage (FM%; β_ilr1 = 0.18; 95% CI: 0.01, 0.34; p = 0.040) and visceral adipose tissue (VAT; β_ilr1 = 0.37; 95% CI: 0.03, 0.71; p = 0.034) were associated with time spent in middle sedentary bouts in duration of 10-29 min (relative to remaining behaviors). No significant associations were found for short (< 10 min) and long sedentary bouts (≥30 min). Substituting the time spent in total SB with moderate-to-vigorous physical activity (MVPA) was associated with a decrease in VAT. Substituting 1 h/week of the time spent in middle sedentary bouts with MVPA was associated with 2.9% (95% CI: 1.2, 4.6), 3.4% (95% CI: 1.2, 5.5), and 6.1% (95% CI: 2.9, 9.2) lower FM%, fat mass index, and VAT, respectively. Moreover, substituting 2 h/week of time spent in middle sedentary bouts with short sedentary bouts was associated with 3.5% (95% CI: 0.02, 6.9) lower FM%.

CONCLUSIONS

Our findings suggest that adiposity status could be improved by increasing MVPA at the expense of time spent in middle sedentary bouts. Some benefits to adiposity may also be expected from replacing middle sedentary bouts with short sedentary bouts, that is, by taking standing or activity breaks more often. These findings may help design more effective interventions to prevent and control childhood obesity.

Implementing a Physical Activity Promoting Program in a Flex-Office: A Process Evaluation with a Mixed Methods Design

The aim of this study was to investigate facilitating and hindering factors when implementing a physical activity (PA)-promoting program among office workers moving to a flex office, by conducting a process evaluation. Additionally, we evaluated self-reported and perceived PA behaviors. With a mixed methods design, analyses were based upon data from interviews with 70 employees and repeated questionnaires from 152 employees. The PA-promoting program was fully implemented and supported by management. There was a strong health promoting culture, encouraging PA in the organization already at the start of the study. The lecture and the office design were rated as the most motivating program components. The use of stairs, breaks during meetings and social acceptance for standing and walking at work increased. Employees described a strive for variation, and how managers, the office environment, productivity and ergonomic aspects influenced sedentary behavior (SB) and PA. The need for the PA-promoting program was questioned, and the timing of the program was debated. To conclude, a strong organizational health culture combined with a facilitating physical environment can create sustainable positive PA behaviors in office settings. A thorough understanding of organizational needs and a participatory process are needed to tailor organizational interventions to decrease SB.

Informing Behaviour Change: What Sedentary Behaviours Do Families Perform at Home and How Can They Be Targeted?

Home-based interventions targeting children's sedentary behaviours have had limited and inconsistent effectiveness, possibly due to a mismatch between the behaviours targeted, the behaviours actually performed, and health-risk messages parents need to initiate change. Between October 2017-February 2018, 540 parents completed an online survey indicating their own and their child's participation in 15 home-based sedentary behaviours (child mean age 11.1 ± 2.61 years, 52% male; parent mean age 40.7 ± 6.14, 93% female). Parents also indicated which home-based sedentary behaviours they and their child could reduce, and what health-risk messages would make them change their child's behaviours. The most prevalent sedentary behaviours among children (particularly older children) and parents were screen-based leisure-time activities, specifically TV/video/DVD use (67.5 and 62.5 min/day, respectively) and using a tablet/smart phone for leisure (53.6 and 80.8 min/day, respectively). Importantly, these were also perceived as the most feasible behaviours parents and children could reduce. Parents reported that the following messages would help them reduce their child's sedentary behaviour: sitting may increase the risk of poor mental health (85.2% of parents) and adversely impact future health as an adult (85.1%). These findings highlight feasible behavioural targets and intervention content for programs aiming to reduce sedentary behaviours in the home environment. Further research is needed to test these strategies.

Substituting prolonged sedentary time and cardiovascular risk in children and youth: a meta-analysis within the International Children's Accelerometry database (ICAD)

BACKGROUND

Evidence on the association between sitting for extended periods (i.e. prolonged sedentary time (PST)) and cardio-metabolic health is inconsistent in children. We aimed to estimate the differences in cardio-metabolic health associated with substituting PST with non-prolonged sedentary time (non-PST), light (LIPA) or moderate-to-vigorous physical activity (MVPA) in children.

METHODS

Cross-sectional data from 14 studies (7 countries) in the International Children's Accelerometry Database (ICAD, 1998-2009) was included. Accelerometry in 19,502 participants aged 3-18 years, together with covariate and outcome data, was pooled and harmonized. Iso-temporal substitution in linear regression models provided beta coefficients (95%CI) for substitution of 1 h/day PST (sedentary time accumulated in bouts > 15 min) with non-PST, LIPA or MVPA, for each study, which were meta-analysed.

RESULTS

Modelling substitution of 1 h/day of PST with non-PST suggested reductions in standardized BMI, but estimates were > 7-fold greater for substitution with MVPA (- 0.44 (- 0.62; - 0.26) SD units). Only reallocation by MVPA was beneficial for waist circumference (- 3.07 (- 4.47; - 1.68) cm), systolic blood pressure (- 1.53 (- 2.42; - 0.65) mmHg) and clustered cardio-metabolic risk (- 0.18 (- 0.3; - 0.1) SD units). For HDL-cholesterol and diastolic blood pressure, substitution with LIPA was beneficial; however, substitution with MVPA showed 5-fold stronger effect estimates (HDL-cholesterol: 0.05 (0.01; 0.10) mmol/l); diastolic blood pressure: - 0.81 (- 1.38; - 0.24) mmHg).

CONCLUSIONS

Replacement of PST with MVPA may be the preferred scenario for behaviour change, given beneficial associations with a wide range of cardio-metabolic risk factors (including adiposity, HDL-cholesterol, blood pressure and clustered cardio-metabolic risk). Effect estimates are clinically relevant (e.g. an estimated reduction in waist circumference of ≈1.5 cm for 30 min/day replacement). Replacement with LIPA could be beneficial for some of these risk factors, however with substantially lower effect estimates.

Exploring when and how adolescents sit: cross-sectional analysis of activPAL-measured patterns of daily sitting time, bouts and breaks

BACKGROUND

This study describes patterns of adolescents' objectively-measured sitting volume, sitting bouts, and breaks in sitting during different days and periods of the day, and explored differences by sex and weekdays versus weekend days.

METHODS

ActivPAL™ data were collected in August 2014-December 2015 from adolescents attending secondary government schools in Melbourne Australia. Eight periods (early morning, mid-morning, morning break, late morning, lunch, early afternoon, late-afternoon and evening) were extracted for each day. School time, class time and out-of-school time were also extracted for weekdays. The percentage of time sitting, percentage of each hour in prolonged sitting (sitting bout ≥10 min), and number of sitting breaks/hour were calculated for each period. Differences by sex, and week and weekend days were determined using t-tests.

RESULTS

Participants (n = 297, 15.4 ± 1.6 years) spent 68% of their day sitting; ~ 30% of each hour in prolonged sitting and 3.1 sitting breaks/hour. Sitting time was greater during class time (75%) and school (70%) compared to out-of-school time (65%). Sitting patterns differed between week and weekend days for all periods except the evening period. Girls had higher proportion of sitting during class than boys (76% vs 72% respectively) and school hours (72% vs 67%), more prolonged sitting during school hours (27% vs 23%), and more sitting breaks per hour during out-of-school time (2.6 vs 2.4), but fewer during class (2.5 vs 3.3) and school hours (2.7 vs 3.3). Sitting patterns did not differ by sex on weekend days.

CONCLUSIONS

Adolescents spent two-thirds of their waking hours sitting, with distinct patterns on weekdays and weekend days. Even though boys and girls were exposed to the same school day routine, girls spent more time sitting and had fewer sitting breaks. Class times, school breaks and the evening period were identified as key intervention periods. Further research is needed to understand the behavioural differences, and guide future intervention design.

Leisure-time sedentary behavior and suicide attempt among 126,392 adolescents in 43 countries

BACKGROUND

Adolescent suicide is a major global mental health problem. Exploring variables associated with suicide attempts is important for the development of targeted interventions. The aim of the current study was to explore associations between leisure-time sedentary behavior and suicide attempts.

METHODS

Data from the Global School-based Student Health Survey were analyzed. Data on past 12-month suicide attempts and self-reported leisure-time sedentary time were collected. Multivariable logistic regression and meta-analysis were conducted to assess the associations.

RESULTS

Among 126,392 students from 43 countries (mean age 13.8 ± 0.96 years; 48.9% female), 10.6% had attempted suicide. The prevalence of suicide attempts increased with increasing sedentary leisure-time per day (from 9% at <1 h/day to 16.8% at >8 h/day). Compared to those engaging in <1 h/day sedentary during leisure-time, there was a dose-dependent increase in odds ratios (ORs) for suicide attempts, with the OR for >8 h/day being 1.45 (95% confidence interval=1.19-1.77).

LIMITATIONS

The study is cross-sectional, therefore the directionality of the relationships cannot be deduced.

CONCLUSIONS

Our data suggest that leisure-time sedentary behavior is associated with increased odds for suicide attempt in adolescence. Future longitudinal data are required to confirm/refute the findings to inform public prevention campaigns.

Energy expenditure associated with posture transitions in preschool children

BACKGROUND

Despite growing scientific interest in the benefits of breaking up sedentary time with intermittent standing or walking, few studies have investigated the energy cost of posture transitions. This study aimed to determine whether posture transitions are associated with increased energy expenditure in preschool children.

METHODS

Forty children (mean age 5.3 ± 1.0y) completed a ~150-min room calorimeter protocol involving sedentary, light, and moderate- to vigorous-intensity activities. This study utilised data from ~65-min of the protocol, during which children were undertaking sedentary behaviours (TV viewing, drawing/colouring in, and playing with toys on the floor). Posture was coded as sit/lie, stand, walk, or other using direct observation; posture transitions were classified as sit/lie to stand/walk, sit/lie to other, stand/walk to other, or vice versa. Energy expenditure was calculated using the Weir equation and used to calculate individualised MET and activity energy expenditure (AEE) values. Spearman's rank correlations were used to compare the number of posture transitions, in the individual activities separately and combined, with corresponding MET and AEE values. Participants were divided into tertiles based on the number of posture transitions; MET and AEE values of children in the lowest and highest tertiles of posture transitions were compared using unpaired t-tests. Effect sizes (Cohen's d) were calculated.

RESULTS

There was a positive correlation between the total number of posture transitions and average METs (rs = 0.42, p = 0.02) and AEE (rs = 0.43, p = 0.02). MET differences between the lowest and highest tertiles of posture transitions resulted in a small effect size for playing with toys (d = 0.27), and moderate effect sizes for TV viewing, drawing and all three activities combined (d = 0.61, 0.50 and 0.64 respectively). Similar results were found for AEE.

CONCLUSIONS

Results from this study showed that variation in posture transitions may be associated with variation in energy expenditure in preschool children. The findings suggest that the concept that variation in posture transitions may have meaningful biological or health effects in early childhood is worth investigating further.

Flexible learning spaces reduce sedentary time in adolescents

OBJECTIVES

Many schools internationally are replacing traditional classrooms (TC) with innovative flexible learning spaces (FLS) to improve academic outcomes. Via a stealth approach, there may be additional unintended health benefits if students reduce their total and prolonged sitting. The aim of this study was to compare student sitting patterns between TC and FLS.

DESIGN

School-based cross-over trial.

METHODS

Students at nine secondary schools (n=191, M age=13.2±1.0years) wore activPAL accelerometers in both a traditionally furnished and arranged classroom (TC), and a FLS containing a variety of furniture and layout options, utilizing student-centered pedagogies, for the duration of one double classroom lesson (M=76min). The lesson content and teacher were consistent across both conditions. Data were analyzed using multilevel mixed-effects linear regression.

RESULTS

In FLS, students spent less class time sitting (mean=18%; 95% CI: -20.8, -15.0), and accumulated more breaks in sitting (2.1; 95% CI: 0.8, 3.5 per 60min), more bouts of intermittent (≤9min) sitting (2.2; 95% CI: 0.8, 3.6 per 60min), and fewer bouts of prolonged (≤30min) sitting (-0.2; 95% CI: -0.3, -0.1 per 60min), than in TC. Students also spent more class time standing (15%; 95% CI: 12.7, 18.0) and stepping (3%; 95% CI: 2.0, 3.1) in FLS than TC.

CONCLUSION

The results suggest that, by stealth, elements of FLS including a variety of furniture and resources, and greater use of student-centered pedagogies, facilitate improvements in adolescents' sedentary profiles during class time. This may translate into beneficial health impacts over a longer period given the health benefits of reducing total and breaking up prolonged sitting.

Longitudinal Changes in Sitting Patterns, Physical Activity, and Health Outcomes in Adolescents

This study examined two-year changes in patterns of activity and associations with body mass index (BMI) and waist circumference (WC) among adolescents. Inclinometers (activPAL) assessed sitting, sitting bouts, standing, stepping, and breaks from sitting. ActiGraph-accelerometers assessed sedentary time (SED), light-intensity physical activity (LIPA, stratified as low- and high-LIPA), and moderate-to-vigorous physical activity (MVPA). Anthropometric measures were objectively assessed at baseline and self-reported at follow-up. Data from 324 and 67 participants were obtained at baseline and follow-up, respectively. Multilevel mixed-effects linear regression models examined changes over time, and associations between baseline values and BMI and WC at follow-up. There were significant increases in BMI (0.6 kg/m²) and durations of prolonged sitting (26.4 min/day) and SED (52 min/day), and significant decreases in stepping (−19 min/day), LIPA (−33 min/day), low-LIPA (−26 min/day), high-LIPA (−6.3 min/day), MVPA (−19 min/day), and the number of breaks/day (−8). High baseline sitting time was associated (p = 0.086) with higher BMI at follow-up. There were no significant associations between baseline sitting, prolonged sitting, LIPA, or MVPA with WC. Although changes in daily activity patterns were not in a favourable direction, there were no clear associations with BMI or WC. Research with larger sample sizes and more time points is needed.

Associations between activity patterns and cardio-metabolic risk factors in children and adolescents: A systematic review

INTRODUCTION

Total volumes of physical activity and sedentary behaviour have been associated with cardio-metabolic risk profiles; however, little research has examined whether patterns of activity (e.g., prolonged bouts, frequency of breaks in sitting) impact cardio-metabolic risk. The aim of this review was to synthesise the evidence concerning associations between activity patterns and cardio-metabolic risk factors in children and adolescents aged 5-19 years.

MATERIALS AND METHODS

A systematic search of seven databases was completed in October 2017. Included studies were required to report associations between objectively-measured activity patterns and cardio-metabolic risk factors in children and/or adolescents, and be published between 1980 and 2017. At least two researchers independently screened each study, extracted data, and undertook risk of bias assessments.

RESULTS

From the 15,947 articles identified, 29 were included in this review. Twenty-four studies were observational (cross-sectional and/or longitudinal); five were experimental. Ten studies examined physical activity patterns, whilst 19 studies examined sedentary patterns. Only one study examined both physical activity and sedentary time patterns. Considerable variation in definitions of activity patterns made it impossible to identify which activity patterns were most beneficial to children's and adolescents' cardio-metabolic health. However, potential insights and current research gaps were identified.

DISCUSSION AND CONCLUSION

A consensus on how to define activity patterns is needed in order to determine which activity patterns are associated with children's and adolescents' cardio-metabolic risk. This will inform future research on the impact of activity patterns on children's and adolescents' short- and longer-term health.

Impact of Wearing Graduated Compression Stockings on Psychological and Physiological Responses during Prolonged Sitting

We investigated the impact of wearing vs. not wearing graduated compression stockings on psychological and physiological responses in 18 healthy young people (12 men and six women) during 3 h prolonged sitting. Profiled of Mood States (POMS) scores did not show marked differences between with and without stockings. A 3 h sit significantly decreased saliva cortisol in both conditions; with no differences between conditions. Wearing stockings suppressed a subjective uncomfortable sensation (e.g., pain; fatigue; swelling) in the lower limbs, as assessed by visual analogue scale (VAS). Increase in heart rate at 1 h and 3 h was significantly greater without than with stockings. In addition, high-frequency oscillations (HF: 0.15–0.4 Hz), used as an indicator of parasympathetic nerve activity, showed higher values with than without stockings throughout the 3 h sitting period—significantly higher at 1 h. When data for both conditions were pooled pre-to-post changes in saliva cortisol were positively associated with higher uncomfortable sensations of VAS in the lower limbs and negatively associated with changes in the Vigor subscale of POMS. Collectively, these findings suggest that wearing graduated compression stockings may benefit from subjective comfort and increased parasympathetic nerve activity.

Sedentary behavior and depressive symptoms among 67,077 adolescents aged 12-15 years from 30 low- and middle-income countries

BACKGROUND

Depression is common and burdensome in adolescents. Understanding modifiable environmental risk factors is essential. There is evidence that physical activity is protective of depression. However, the impact of sedentary behavior (SB) on depression is relatively under-researched especially in low- and middle-income countries (LMICs). In this cross-sectional study, we explored the association between SB and depressive symptoms in adolescents from 30 LMICs, controlling for confounders including physical activity.

METHOD

Data from the Global school-based Student Health Survey were analyzed in 67,077 adolescents [mean (SD) age 13.8 (0.9) years; 50.6% girls). Self-report measures assessed depressive symptoms during the past 12 months, and SB, which was a composite variable assessing time spent sitting and watching television, playing computer games, talking with friends during a typical day excluding the hours spent sitting at school and doing homework. Multivariable logistic regression analysis was conducted and a countrywide meta-analysis undertaken.

RESULTS

The prevalence of depressive symptoms and ≥ 3 h/day of SB were 28.7 and 30.6%, respectively. There was a linear increase in the prevalence of depressive symptoms with increasing sedentary time beyond ≥3 h/day (vs. < 1 h/day). Among boys, 1-2 h/day of SB was associated with lower odds for depression (vs. < 1 h/day). Countrywide meta-analysis demonstrated that spending ≥3 h/day versus < 3 h/day was associated with a 20% increased odds for depressive symptoms (OR = 1.20; 95% CI = 1.16-1.24) with low between-country heterogeneity (I2 = 27.6%).

CONCLUSION

Our data indicate that being sedentary for ≥3 h/day is associated with increased odds for depressive symptoms in adolescence. Future longitudinal data are required to confirm/refute the findings to inform public interventions which aim to limit the time spent being sedentary in adolescents.

Evaluation of an intervention to reduce adolescent sitting time during the school day: The 'Stand Up for Health' randomised controlled trial

OBJECTIVES

Adolescents spend large proportions of the school day sitting; potentially increasing their health risks. This study aimed to evaluate the feasibility, acceptability and potential efficacy of a school-based intervention to reduce adolescent sitting time during the school day.

DESIGN

Two-arm parallel-group randomised controlled trial.

METHODS

Adolescents (13-16 years) were recruited from four private high schools in New South Wales, Australia. Schools were pair-matched and randomised to treatment or control. Research assistants were blinded to intervention aims and treatment allocation. Intervention initiatives included classroom and outdoor environmental measures to break up and reduce the proportion of adolescent school time spent sitting. Teacher and students surveys assessed intervention feasibility, acceptability and potential efficacy. Proportional sitting time was the primary outcome, measured by activPAL monitors, worn for one week during the school day. Secondary outcomes included body mass index, body fatness, working memory and non-verbal reasoning. Data were analysed using a general linear model for continuous variables and adjusted for clustering.

RESULTS

While teachers and students supported the program, process evaluation results indicate aspects of the intervention were not implemented with fidelity. Eighty-eight adolescents (M_age=14.7±0.7, 50% male) participated in the trial. Eighty-six had valid data for all variables (43 controls, 43 intervention). There was no significant intervention effect on the primary outcome. There was a significant effect on working memory (adjusted difference ±SD=-0.42±1.37; p=0.048 (Cohen's d)=0.31).

CONCLUSIONS

These findings contribute to limited research in this area, providing guidance for future interventions in the high school environment.

TRIAL REGISTRATION

The study was registered with the Australian and New Zealand Clinical Trials Registry (ACTRN 12614001001684).

Improving Cardiometabolic Health with Diet, Physical Activity, and Breaking Up Sitting: What about Sleep?

Cardiometabolic disease poses a serious health and economic burden worldwide and its prevalence is predicted to increase. Prolonged sitting, lack of physical activity, poor diet, and short sleep duration are ubiquitous behaviors in modern society, and all are independent risk factors in the development of cardiometabolic disease. Existing evidence demonstrates that breaking up prolonged periods of sitting is beneficial for cardiometabolic health, however, studies have not controlled for prior sleep duration. This article examines how prolonged sitting and short sleep duration independently contribute to cardiometabolic risk, and how breaking up sitting and obtaining adequate sleep may reduce this risk. We suggest that as prolonged sitting and short sleep duration influence the same cardiometabolic parameters, there is potential for short sleep to attenuate the positive impact of breaking up prolonged sitting with physical activity. Likewise, breaking up prolonged sitting and obtaining adequate sleep together could improve predictors of cardiometabolic disease, i.e., the combined effect may be stronger than either alone. To explore these perspectives, we propose a research agenda to investigate the relationship between breaking up prolonged sitting with physical activity and short sleep duration. This will provide an evidence-base for informing the design of interventions to reduce the burden of cardiometabolic disease on communities worldwide.