University of Jyväskylä

Dissertation: 29.9.2017 Sit-stand workstations: effects on occupational sitting time, potential health benefits, and acute postural physiology (Gao)

Start date: Sep 29, 2017 12:00 PM

End date: Sep 29, 2017 03:00 PM

Location: Seminaarinmäki, Liikunta, L302

Ying GaoM.Sc. Ying Gao defends her doctoral dissertation in Biomechanics “Sit-stand workstations: effects on occupational sitting time, potential health benefits, and acute postural physiology”. Opponent Professor Marie Murphy (Ulster University, United Kingdom of Great Britain) and custos Professor Taija Juutinen (University of Jyväskylä). The doctoral dissertation is held in English.

Given that a high amount of sedentary behavior is a global health issue, reducing sitting time is emerging as a novel intervention strategy and a workplace health priority. Sit-stand workstations have been introduced to the workplace, and can be used to rotate between sitting and standing postures at work. It is important to develop and evaluate sit-stand interventions that aim to induce behavioral changes and potential health benefits, in order to effectively implement them into practice.

Therefore, this thesis examined whether and to what extent sit-stand workstations can reduce occupational sitting and improve health indexes in a real workplace. The thesis included four studies in field and laboratory settings using several methodological approaches such as EMG and accelerometry to examine: 1) validity of self-report occupational sitting time (n = 70); 2) intervention effectiveness (n = 45); 3) comparison of muscle activity patterns and spinal loading (n = 24); 4) acute physiological responses to sitting and standing (n = 18). Overall, occupational sitting represented ~80% or less of daily work hours among office-based workers. A validation study using long-term questionnaire and short-term daily recall showed that while at the group level both of these self-reported measures are acceptable (< 3% difference compared to thighmounted accelerometry) for assessing the proportion of work time spent sitting, they are not necessarily reliable at an individual level due to large individual variability.

When the questionnaire was used in a 6-month intervention study, working at a sitstand workstation led to a ~7% reduction in occupational sitting, and improved perceived musculoskeletal comfort and work ability in office workers. About 42% of the participants who had a sit-stand desk used its function on a daily basis and showed ~14% reduction in sitting time. The cross-sectional comparison study showed that office workers using sit–stand workstations had ~15% less muscle inactivity time and ~11% more light muscle activity time during one work day, but the same amount of spinal shrinkage compared to office workers using sit workstations. In a laboratorybased randomized crossover trial, two hours of standing as compared to seated work increased muscle activity, energy expenditure and circulating glucose level after glucose loading. The results highlighted fuel switching in favor of fat oxidation during standing, in spite of extra carbohydrate availability. In conclusion, using sit-stand workstations seems to be a promising strategy to reduce occupational sitting time and improve health-related outcomes, although more studies are required to address the best practices for implementing these workstations into workplace settings.

Keywords: EMG, intervention, muscle inactivity, occupational sitting, postural physiology, self-report, workplace

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Ying Gao
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