Background: Prolonged sitting time is associated with poor health outcomes, such as reduced life expectancy, increased all-cause mortality and cardiovascular disease. Both total sitting time and the way sitting time is accumulated throughout the day (sitting patterns) play a role in health outcomes.1,2 Understanding not only the effect of prolonged sitting, but patterns of sitting is therefore an important research direction. With the modern workplace a setting in which high volumes of sitting time occurs, office environments are important contexts to investigate the role sitting patterns play in health outcomes.
Aim: This aim of this thesis is to measure and describe sitting patterns in Australian desk-based office workers and to assess strategies for change. This aim will be addressed by a suite of four studies; the development and validation of a novel measure of desk-based occupational sitting; two cross sectional studies, one describing the usual patterns of sitting time in desk-based office workers; and the other examining the association between desk-based sitting and weight related outcomes; and, finally, a review to assess strategies for changing occupational sitting.
Methods and results: Study one: As part of this PhD, a novel measure of occupational sitting was developed, called the sitting pad (SP); a chair-based pressure sensor and microcontroller, with intervention capabilities to prompt employees to get up from sitting. The aim of study one was to test the validity of the SP to measure desk-based patterns against camera-derived direct observation; and to compare the data with those from inclinometers in other devices that measure sitting patterns, the ActivPAL (AP) and ActiGraph GT3X+ (AG). A camera recorded desk-based sitting time and transitions to and from sitting (STS) during a prescribed and a free-living office protocol. The findings indicated that the SP provided highly accurate measures of desk-based sitting time and STS in both the prescribed (mean difference; sitting time 0.30 ± 0.21 minutes, STS -0.46 ± 0.78) and free-living protocols (ICC; sitting time 0.999, STS 0.997). The AP was also shown to be an accurate measure of sitting patterns. In contrast, the AG inclinometer was unable to measure sitting time or STS accurately during either protocol. The SP therefore provides an accurate and novel measure for research into occupational sitting patterns.
Study two: The validated SP was then used in a cross-sectional study to describe sitting patterns of desk-based employees (n=105). Sitting at the desk (SP) and in other work contexts (AP) was measured for an entire working week. Employees used a diary to record work and waking hours. Time spent awake, at work, sitting at work and at the desk; number of STS at the desk; and number of bouts of continuous sitting at the desk >20 and >60 minutes, were calculated. The findings indicated that employees spent the majority of their working day sitting at their desks (5.8±1.2 hours per day) and that sitting was regularly interrupted (29±13 STS per day). Sitting for more than 60 consecutive minutes occurred infrequently (0.69±0.62 times per day), with 80% of STS occurring before 20 minutes of continuous sitting was reached. The results also suggested wide variability within and between employees in relation to desk-based sitting patterns. The findings provide highly detailed insights into desk-based sitting habits, highlighting large proportions of time spent sitting at desks, but with frequent interruptions.
Study three: In this study, secondary analyses of the previously collected cross-sectional data were performed. In addition to the objective assessment of sitting patterns, employees were provided with a health check where waist circumference (WC), height and weight were measured, and BMI calculated (kg/m2). Associations between sitting patterns, WC and BMI were tested using logistic regression models. The findings suggested that those with high desk-based sitting time (≥352.15 minutes per day) were almost three times more likely to have WC ≥94 cm (men) or ≥80cm (women), and nine times more likely to have BMI ≥30, than those with lower sitting time. There were no significant associations between the number of STS at the desk and WC or BMI. The results suggest that, in this population, high desk-based sitting time was associated with an increased risk of obesity, whereas frequency of getting up from the desk was not.
Study four: Building on the measurement and understanding issues explored in studies one to three, the final study consisted of two reviews that were conducted to assess effective intervention strategies to change occupational sitting patterns. The first was a review of occupational sitting interventions. The second drew on the substantial body of evidence from the workplace physical activity literature and assessed study components of interventions with high recruitment rates. Electronic and manual searches were conducted in both reviews. Seven occupational sitting intervention studies were reported. Successful studies intervened at the desk and typically used height adjustable standing desks. Intervention studies from the physical activity literature (n=30 studies), suggested that organisationally-driven employee involvement and providing behaviour change interventions during paid time as part of workplace policies and practices, increase the likelihood of influencing health behaviours at a population level.
Conclusion: As part of this thesis, a highly accurate and novel measure of desk-based occupational sitting patterns was developed. Using this device, it was demonstrated that, in this sample, employees spent most of their working hours sitting at the desk. However, usual desk-based sitting was frequently interrupted and sitting patterns were highly variable. Despite these frequent interruptions, employees who sit for long periods of time at the desk were at increased risk of weight-related health outcomes. Future interventions should aim to reduce sitting time at the desk, and may include strategies such as the implementation of height adjustable standing desks, in conjunction with organisationally-driven sitting policies and practices, utilising the SP to provide employees with real time prompts. References: 1. Healy GN, Dunstan DW, Salmon J, et al. Breaks in sedentary time - Beneficial associations with metabolic risk. Diabetes Care. 2008;31(4):661-666. 2. Healy GN, Matthews CE, Dunstan DW, et al. Sedentary time and cardio-metabolic biomarkers in US adults: NHANES 2003-06. European Heart Journal. 2011;32(5):590-597.