Showing papers by "David W. Dunstan published in 2013"

Light-Intensity Physical Activity and Cardiometabolic Biomarkers in US Adolescents

Abstract: Background The minimal physical activity intensity that would confer health benefits among adolescents is unknown. The purpose of this study was to examine the associations of accelerometer-derived light-intensity (split into low and high) physical activity, and moderate- to vigorous-intensity physical activity with cardiometabolic biomarkers in a large population-based sample. Methods The study is based on 1,731 adolescents, aged 12–19 years from the 2003/04 and 2005/06 National Health and Nutrition Examination Survey. Low light-intensity activity (100–799 counts/min), high light-intensity activity (800 counts/min to <4 METs) and moderate- to vigorous-intensity activity (≥4 METs, Freedson age-specific equation) were accelerometer-derived. Cardiometabolic biomarkers, including waist circumference, systolic blood pressure, diastolic blood pressure, HDL-cholesterol, and C-reactive protein were measured. Triglycerides, LDL- cholesterol, insulin, glucose, and homeostatic model assessments of β-cell function (HOMA-%B) and insulin sensitivity (HOMA-%S) were also measured in a fasting sub-sample (n = 807). Results Adjusted for confounders, each additional hour/day of low light-intensity activity was associated with 0.59 (95% CI: 1.18–0.01) mmHG lower diastolic blood pressure. Each additional hour/day of high light-intensity activity was associated with 1.67 (2.94–0.39) mmHG lower diastolic blood pressure and 0.04 (0.001–0.07) mmol/L higher HDL-cholesterol. Each additional hour/day of moderate- to vigorous-intensity activity was associated with 3.54 (5.73–1.35) mmHG lower systolic blood pressure, 5.49 (1.11–9.77)% lower waist circumference, 25.87 (6.08–49.34)% lower insulin, and 16.18 (4.92–28.53)% higher HOMA-%S. Conclusions Time spent in low light-intensity physical activity and high light-intensity physical activity had some favorable associations with biomarkers. Consistent with current physical activity recommendations for adolescents, moderate- to vigorous-intensity activity had favorable associations with many cardiometabolic biomarkers. While increasing MVPA should still be a public health priority, further studies are needed to identify dose-response relationships for light-intensity activity thresholds to inform future recommendations and interventions for adolescents.

Effects of breaking up prolonged sitting on skeletal muscle gene expression

Abstract: Breaking up prolonged sitting has been beneficially associated with cardiometabolic risk markers in both observational and intervention studies. We aimed to define the acute transcriptional events induced in skeletal muscle by breaks in sedentary time. Overweight/obese adults participated in a randomized three-period, three-treatment crossover trial in an acute setting. The three 5-h interventions were performed in the postprandial state after a standardized test drink and included seated position with no activity and seated with 2-min bouts of light- or moderate-intensity treadmill walking every 20 min. Vastus lateralis biopsies were obtained in eight participants after each treatment, and gene expression was examined using microarrays validated with real-time quantitative PCR. There were 75 differentially expressed genes between the three conditions. Pathway analysis indicated the main biological functions affected were related to small-molecule biochemistry, cellular development, growth and proliferation, and carbohydrate metabolism. Interestingly, differentially expressed genes were also linked to cardiovascular disease. For example, relative to prolonged sitting, activity bouts increased expression of nicotamide N-methyltransferase, which modulates anti-inflammatory and anti-oxidative pathways and triglyceride metabolism. Activity bouts also altered expression of 10 genes involved in carbohydrate metabolism, including increased expression of dynein light chain, which may regulate translocation of the GLUT-4 glucose transporter. In addition, breaking up sedentary time reversed the effects of chronic inactivity on expression of some specific genes. This study provides insight into the muscle regulatory systems and molecular processes underlying the physiological benefits induced by interrupting prolonged sitting.

Reducing office workers’ sitting time: rationale and study design for the Stand Up Victoria cluster randomized trial

Abstract: Excessive time spent in sedentary behaviours (sitting or lying with low energy expenditure) is associated with an increased risk for type 2 diabetes, cardiovascular disease and some cancers. Desk-based office workers typically accumulate high amounts of daily sitting time, often in prolonged unbroken bouts. The Stand Up Victoria study aims to determine whether a 3-month multi-component intervention in the office setting reduces workplace sitting, particularly prolonged, unbroken sitting time, and results in improvements in cardio-metabolic biomarkers and work-related outcomes, compared to usual practice. A two-arm cluster-randomized controlled trial (RCT), with worksites as the unit of randomization, will be conducted in 16 worksites located in Victoria, Australia. Work units from one organisation (Department of Human Services, Australian Government) will be allocated to either the multi-component intervention (organisational, environmental [height-adjustable workstations], and individual behavioural strategies) or to a usual practice control group. The recruitment target is 160 participants (office-based workers aged 18–65 years and working at least 0.6 full time equivalent) per arm. At each assessment (0- [baseline], 3- [post intervention], and 12-months [follow-up]), objective measurement via the activPAL3 activity monitor will be used to assess workplace: sitting time (primary outcome); prolonged sitting time (sitting time accrued in bouts of ≥30 minutes); standing time; sit-to-stand transitions; and, moving time. Additional outcomes assessed will include: non-workplace activity; cardio-metabolic biomarkers and health indicators (including fasting glucose, lipids and insulin; anthropometric measures; blood pressure; and, musculoskeletal symptoms); and, work-related outcomes (presenteeism, absenteeism, productivity, work performance). Incremental cost-effectiveness and identification of both workplace and individual-level mediators and moderators of change will also be evaluated. Stand Up Victoria will be the first cluster-RCT to evaluate the effectiveness of a multi-component intervention aimed at reducing prolonged workplace sitting in office workers. Strengths include the objective measurement of activity and assessment of the intervention on markers of cardio-metabolic health. Health- and work-related benefits, as well as the cost-effectiveness of the intervention, will help to inform future occupational practice. ACTRN1211000742976

Don't take cancer sitting down: a new survivorship research agenda.

Abstract: Cancer survival is associated with considerable physical and psychosocial burden. Broadly accessible, nonpharmacologic measures that may extend disease-free survival, limit comorbid disease, and enhance quality of life are required. Sedentary behavior (too much sitting) is now understood to be a health risk that is additional to, and distinct from, the hazards of too little exercise. Of particular note, it is associated with adiposity, insulin resistance, and markers of inflammation. Therefore, it is plausible that sedentary behavior may contribute to adverse cancer outcomes (disease progression, recurrence, or death) and to the development of comorbid chronic disease. Initial studies indicate that cancer survivors spend two-thirds of their waking hours sitting. Among colorectal cancer survivors, sedentary behavior may contribute to all-cause and disease-specific mortality, weight gain, comorbid cardiovascular disease, and diminished quality of life. There is a need for dose-response evidence, and for a broader understanding of the underlying mechanisms by which prolonged sitting time may affect cancer survivors' health.

Does an 'Activity-Permissive' Workplace Change Office Workers' Sitting and Activity Time?

Abstract: Introduction: To describe changes in workplace physical activity, and health-, and work-related outcomes, in workers who transitioned from a conventional to an 'activity-permissive' workplace.

Examination of mid-intervention mediating effects on objectively assessed sedentary time among children in the Transform-Us! cluster-randomized controlled trial.

Abstract: Background: The optimal targets and strategies for effectively reducing sedentary behavior among young people are unknown. Intervention research that explores changes in mediated effects as well as in outcome behaviors is needed to help inform more effective interventions. Therefore, the purpose of this study was to examine the mid-intervention mediating effects on children’s objectively assessed classroom and total weekday sedentary time in the Transform-Us! intervention. Methods: The results are based on 293 children, aged 7- to 9-years-old at baseline, from 20 schools in Melbourne, Australia. Each school was randomly allocated to one of four groups, which targeted reducing sedentary time in the school and family settings (SB; n = 74), increasing or maintaining moderate- to vigorous-intensity physical activity in the school and family settings (PA; n = 75), combined SB and PA (SB + PA; n = 80), or the current practice control (C; n = 64). Baseline and mid-intervention data (5–9 months) were collected in 2010 and analyzed in 2012. Classroom and total weekday sedentary time was objectively assessed using ActiGraph accelerometers. The hypothesized mediators including, child enjoyment, parent and teacher outcome expectancies, and child perceived access to standing opportunities in the classroom environment, were assessed by questionnaire. Results: The SB + PA group spent 13.3 min/day less in weekday sedentary time at mid-intervention compared to the control group. At mid-intervention, children in the SB group had higher enjoyment of standing in class (0.9 units; 5-unit scale) and all intervention groups had more positive perceptions of access to standing opportunities in the classroom environment (0.3-0.4 units; 3-unit scale), compared to the control group. However, none of the hypothesized mediator variables had an effect on sedentary time; thus, no mediating effects were observed. Conclusions: While beneficial intervention effects were observed on some hypothesized mediating variables and total weekday sedentary time at mid-intervention, no significant mediating effects were found. Given the dearth of existing information, future intervention research is needed that explores mediated effects. More work is also needed on the development of reliable mediator measures that are sensitive to change overtime. Trial registration: ACTRN12609000715279 ISRCTN83725066

The effect of interrupting prolonged sitting time with short, hourly, moderate-intensity cycling bouts on cardiometabolic risk factors in healthy, young adults

Abstract: Although detrimental associations of sitting time and health indicators have been observed in young adults, evidence of pathophysiological mechanisms is lacking. Therefore, this study tested the hypothesis that the acute cardiometabolic effects of prolonged sitting can be compensated by hourly interruptions to sitting in healthy, young adults. Additionally, leg muscle activation during sitting and moderate-intensity physical activity interruptions was assessed. Eleven apparently healthy adults (18-24 yr; five men/six women) participated in this randomized, crossover study, involving two experimental conditions: 1) 8 h prolonged sitting and 2) 8 h of sitting, interrupted with hourly, 8-min, moderate-intensity cycling exercise bouts. In both conditions, participants consumed two standardized, high-fat mixed meals after 1 and 5 h. Capillary blood samples were collected hourly during each 8-h experimental condition. Muscle activity was measured using electromyography. Muscle activity during cycling was seven to eight times higher compared with rest. Postprandial levels of C-peptide were significantly lower (unstandardized regression coefficient = -0.19; confidence interval = [-0.35; -0.03]; P = 0.017) during interrupted sitting compared with prolonged sitting. Postprandial levels of other cardiometabolic biomarkers (e.g., glucose, triglycerides, cholesterol) were not significantly different between conditions. Hourly physical activity interruptions in sitting time, requiring a muscle activity of seven to eight times the resting value, led to an attenuation of postprandial C-peptide levels but not for other cardiometabolic biomarkers compared with prolonged sitting in healthy, young adults. Whether this acute effect transfers to chronic effects over time is unknown.

Adults' past-day recall of sedentary time: reliability, validity, and responsiveness.

Abstract: Purpose: Past-day recall rather than recall of past week or a usual/typical day may improve the validity of self-reported sedentary time measures. This study examined the test-retest reliability, criterion validity, and responsiveness of the seven-item questionnaire, Past-day Adults' Sedentary Time (PAST). Methods: Participants (breast cancer survivors, n = 90, age = 33-75 yr, body mass index = 25-40 kg.m(-2)) in a 6-month randomized controlled trial of a lifestyle-based weight loss intervention completed the interviewer-administered PAST questionnaire about time spent sitting/lying on the previous day for work, transport, television viewing, nonwork computer use, reading, hobbies, and other purposes (summed for total sedentary time). The instrument was administered at baseline, 7 d later for test-retest reliability (n = 86), and at follow-up. ActivPAL3-assessed sit/lie time in bouts of >= 5 min during waking hours on the recall day was used as the validity criterion measure at both baseline (n = 72) and follow-up (n = 68). Analyses included intraclass correlation coefficients, Pearson's correlations (r), and Bland-Altman plots and responsiveness index. Results: The PAST had fair to good test-retest reliability (intraclass correlation coefficient = 0.50, 95% confidence interval [CI] = 0.32-0.64). At baseline, the correlation between PAST and activPAL sit/lie time was r = 0.57 (95% CI = 0.39-0.71). The mean difference between PAST at baseline and retest was -25 min (5.2%), 95% limits of agreement = -5.9 to 5.0 h, and the activPAL sit/lie time was -9 min (1.8%), 95% limits of agreement = -4.9 to 4.6 h. The PAST showed small but significant responsiveness (-0.44, 95% CI = -0.92 to -0.04); responsiveness of activPAL sit/lie time was not significant. Conclusion: The PAST questionnaire provided an easy-to-administer measure of sedentary time in this sample. Validity and reliability findings compare favorably with other sedentary time questionnaires. Past-day recall of sedentary time shows promise for use in future health behavior, epidemiological, and population surveillance studies.

Impact on Hemostatic Parameters of Interrupting Sitting with Intermittent Activity.

Abstract: INTRODUCTION: Excessive sitting has been associated with an elevated risk of vascular conditions, particularly venous thrombosis. Interrupting sitting time with intermittent physical activity can reduce venous stasis; however, impacts on other aspects of thrombogenesis are less understood. PURPOSE: To examine the effects of interrupting sitting time on blood coagulation and blood volume parameters in sedentary, middle-age, overweight/obese adults (11 men and 8 women; age = 53.8 ± 4.9 yr, body mass index = 31.2 ± 4.1 kg·m; mean ± SD). METHODS: The randomized three-period, three-treatment acute crossover trial consisted of uninterrupted sitting and sitting interrupted by 2-min bouts of either light- or moderate-intensity treadmill walking every 20 min. In each trial condition, blood samples were collected at baseline before the consumption of a standardized meal (-2 h) and postintervention (5 h). RESULTS: Plasma fibrinogen increased from baseline with uninterrupted sitting (0.24 g·L-1, 95% confidence interval = 0.13-0.34, P < 0.001). Light-intensity but not moderate-intensity activity breaks attenuated the increase by 0.17 g·L-1 (95% confidence interval = 0.01-0.32, P < 0.05). There were no between-condition differences in prothrombin time, activated partial thromboplastin time, von Willebrand factor, D-dimer, or platelet count. Uninterrupted sitting reduced plasma volume and increased hematocrit, hemoglobin, and red blood cell count; effects attenuated by both light- and moderate-intensity breaks (P < 0.05). White blood cell count increased with uninterrupted sitting and further increased with moderate-intensity breaks. Mean platelet volume increased with moderate-intensity but not light-intensity breaks or uninterrupted sitting. CONCLUSION: Uninterrupted sitting increased fibrinogen and reduced plasma volume, with associated increases in hemoglobin and hematocrit. Activity breaks attenuated these responses, indicative of an ameliorating influence on the procoagulant effects of uninterrupted sitting. Copyright

Television viewing and low leisure-time physical activity in adolescence independently predict the metabolic syndrome in mid-adulthood

Abstract: OBJECTIVE We investigated whether television (TV) viewing and low leisure-time physical activity in adolescence predict the metabolic syndrome in mid-adulthood.RESEARCH DESIGN AND METHODS TV viewin ...

Independent and joint associations of TV viewing time and snack food consumption with the metabolic syndrome and its components; a cross-sectional study in Australian adults

Abstract: Background: Television (TV) viewing time is positively associated with the metabolic syndrome (MetS) in adults. However, the mechanisms through which TV viewing time is associated with MetS risk remain unclear. There is evidence that the consumption of energy-dense, nutrient poor snack foods increases during TV viewing time among adults, suggesting that these behaviors may jointly contribute towards MetS risk. While the association between TV viewing time and the MetS has previously been shown to be independent of adult’s overall dietary intake, the specific influence of snack food consumption on the relationship is yet to be investigated. The purpose of this study was to examine the independent and joint associations of daily TV viewing time and snack food consumption with the MetS and its components in a sample of Australian adults. Methods: Population-based, cross-sectional study of 3,110 women and 2,572 men (>35 years) without diabetes or cardiovascular disease. Participants were recruited between May 1999 and Dec 2000 in the six states and the Northern Territory of Australia. Participants were categorised according to self-reported TV viewing time (low: 0-2 hr/d; high: >2 hr/d) and/or consumption of snack foods (low: 0-3 serves/d; high: >3 serves/d). Multivariate odds ratios [95% CI] for the MetS and its components were estimated using gender-specific, forced entry logistic regression. Results: OR [95% CI] for the MetS was 3.59 [2.25, 5.74] (p≤0.001) in women and 1.45 [1.02, 3.45] (p = 0.04) in men who jointly reported high TV viewing time and high snack food consumption. Obesity, insulin resistance and hypertension (women only) were also jointly associated with high TV viewing time and high snack food consumption. Further adjustment for diet quality and central adiposity maintained the associations in women. High snack food consumption was also shown to be independently associated with MetS risk [OR: 1.94 (95% CI: 1.45, 2.60), p < 0.001] and hypertension [OR: 1.43 (95% CI: 1.01, 2.02), p = 0.05] in women only. For both men and women, high TV viewing time was independently associated with the MetS and its individual components (except hypertension).

Six-month outcomes from Living Well with Diabetes: a randomized trial of a telephone-delivered weight loss and physical activity intervention to improve glycemic control

Abstract: Intensive lifestyle intervention trials in type 2 diabetes contribute evidence on what can be achieved under optimal conditions, but are less informative for translation in applied settings. Living Well with Diabetes is a telephone-delivered weight loss intervention designed for real-world delivery. This study is a randomized controlled trial of telephone counseling (n = 151) versus usual care (n = 151); 6-month primary outcomes of weight, physical activity, HbA1c; secondary diet outcomes; analysis was by adjusted generalized linear models. Relative to usual care, telephone counseling participants had small but significantly better weight loss [−1.12 % of initial body weight; 95 % confidence interval (CI) −1.92, −0.33 %]; physical activity [relative rate (RR) = 1.30; 95 % CI, 1.08, 1.57]; energy intake reduction (−0.63 MJ/day; 95 % CI, −1.01, −0.25); and diet quality (3.72 points; 95 % CI, 1.77, 5.68), with no intervention effect for HbA1c (RR = 0.99; 95 % CI, 0.96, 1.01). Results are discussed in light of challenges to intervention delivery.

Associations of strength training with impaired glucose metabolism: the AusDiab Study.

Abstract: Purpose: To examine the association of strength training (ST) activity with impaired glucose metabolism (IGM) in Australian adults. Methods: On the basis of an oral glucose tolerance test, IGM (which includes impaired fasting glucose, impaired glucose tolerance, or newly diagnosed type 2 diabetes), was assessed in 5831 adults (mean age = 56.0 T 12.7 yr) without clinically diagnosed diabetes who participated in the 2004-2005 Australian Diabetes, Obesity and Lifestyle Study (AusDiab). Meeting the current ST guideline was based on reporting ST at least two times per week (frequency) or ≥40 min·wk in total (duration). Multiple logistic regression analyses examined associations of self-reported ST frequency and duration with IGM. Results: After adjustment for known confounding factors and total moderate-to vigorous-intensity leisure time exercise, the odds ratio (OR) of IGM was 0.73 (95% confidence interval [CI] = 0.59-0.91, P 0.005) in those who met the ST frequency guideline (two or more times per week) and 0.69 (95% CI = 0.55-0.87, P ≤ 0.01) in those who met the ST duration guideline (Q40 minwk). Those who achieved both the recommended frequency and duration of ST had 24% lower odds of IGM. There was also evidence that a moderate frequency (once a week) and duration (10-39 minwk) of ST reduced the odds of IGM (OR frequency = 0.53, 95% CI = 0.51-0.81, P ≤ 0.01; OR duration = 0.72, 95% CI = 0.52-1.00, P ≤ 0.05). Conclusions: These findings support the importance of including ST activity, at a frequency of at least once per week, within exercise management recommendations for the maintenance of favorable metabolic health, particularly as it may contribute to reducing the risk of developing type 2 diabetes mellitus.

New worlds and old prejudices: Australia, cricket and the subcontinent: 1880-1960

Abstract: Until recently, Australia's cricketing past has been coloured by an anglocentric bias. Australian cricket writers, players and administrators mainly have deemed Australian series with subcontinental countries of much lesser importance than Ashes contests. In surveying Australia's cricketing relations with the subcontinent from the 1880s until Australia's first fully fledged official tour of the region in 1959–1960, this paper seeks to redress this imbalance. The paper explores how initial cricketing relations were viewed within the prism of Australia's traditional cricketing ties with England. This did not alter with India's attaining official Test match status in the 1930s. Australian tours of India were confined to unofficial teams, and it was not until 1947–1948 that the first official exchange occurred. As this paper documents, the importance of subcontinental cricket tours increased after the war, as both Labor and Liberal Coalition governments encouraged the use of cricket to foster diplomatic ties ...