What is the Metabolic Cost of Sitting, Standing, and Sit/Stand Transitions? A Randomized Controlled Trial

Introduction Regular physical activity (PA) positively influences most physiological processes in the human body. Inversely, sedentary behavior (SB)-too much sitting as distinct from too little physical activity-contributes adversely to cardio metabolic health outcomes and premature mortality [1-3]. Obesity results from a long-term excess of energy consumed vs. energy expended, a positive energy balance [4]. While overeating certainly contributes to a positive energy balance, the epidemic of obesity and related metabolic disorders is also driven by reductions in energy expended [5]. Modern human environments are vastly different from those of our ancestors. Technologic developments in transportation, communications, workplaces, and home entertainment confer a wealth of comfort, but increase the time spent in SB which represents costs to human health [6]. With increased use of computers, office workers may remain seated for long periods of time during which metabolic cost (MC) is minimal, making many worksites obesogenic environments [7]. Sitting time not only contributes to positive energy balance but is also an independent risk factor for excess adiposity [8,9] and obesity [10] even among people participating in high levels of moderate-to-vigorous physical activity (MVPA) [11,12]. Even without performing exercise people can have markedly variable low intensity physical activity (LIPA) levels, which in turn substantially varies PA energy expenditure (PAEE) by up to 2000 kcal/day [13]. Emerging evidence supports the feasibility of raising daily MC by replacing office work-related SB with LIPA via workstation alternatives to the traditional office chair and desktop computer-based combinations [14].

Regardless of total sitting time, evidence has been growing on the metabolic benefits of interrupting sitting time more often [15-17], with less focus on MC as a result from these breaks. There is some basic science on the differences of MC associated with "sitting" and "standing", however the results are contradictory [14,18]. Also, other alternatives have been investigated [14,19] and it seems that in terms of MC, sitting on a stability ball or using sit-stand/standing desks are comparable to the traditional seated condition EE (≅1.2 kcal min(-1)). The treadmill and pedal desks (active workstation alternatives) have been shown to offer the greatest promise in terms of EE (≅2-4 kcal min(-1)) [14]. Another strategy is to introduce walking breaks into prolonged sedentary time which according to a recent study [20] can yield an additional 24, 59 or 132 kcal per day, if they stood up and walked at a normal, self-selected pace for one, two or five minutes compared with sitting for the 8-hour working period. From this intervention, heart rate (HR) was also examined to assess differences between conditions with no significant between-condition differences for heart rate. Therefore, taking breaks from sitting is a potential outlet to prevent obesity and the rise of obesity but the real contribution of the simple action of standing up from a seated position and returning to the seated position (sit/stand transition) on MC and HR is yet to be investigated. To overcome these limitations, a randomized controlled trial will be conducted to examine the MC and HR associated with sitting, standing, and transitions between the previous behaviors in laboratory settings and using accurate methods (indirect calorimetry). By including this methodological approach we will be able to estimate the additional contribution of a "break" compared to just standing when accumulating sedentary time on MC and HR [18].

Hypothesis

1. The percent increase in MC and heart rate (HR) above resting associated with sitting, standing and sitting/stand transitions will be different, independently of gender, body composition, and age.
2. The MC, either per kg of body weight or per kg of fat-free mass, associated with sitting and standing will be similar but a higher cost is expected for the sitting-to-stand transitions, regardless of gender, age, and FFM.

Purposes