Sedentary behavior, characterized by excess sitting time during waking hours, is detrimental to health and increases cardiometabolic disease (e.g., type 2 diabetes) risk, independent of moderate-to-vigorous physical activity. The mechanisms that mediate this are unknown and there are no evidence-based methods known for effectively intervening on sedentary behavior. The consequences of prolonged sitting time are of particular interest in older adults as sedentary behavior and cardiometabolic disease risk both increase with aging and moderate-to-vigorous physical activity may not be feasible. The investigators propose pilot and feasibility testing of interventions for sedentary older adults that are designed to interrupt prolonged sitting time. Interrupting sitting time through sit-to-stand transitions, and standing and walking breaks increases muscle use and blood flow in the lower parts of the body. Thus, the investigators believe that frequent sit-to-stand interruptions of sitting time are the most efficacious sedentary behavior interventions, compared to simply reducing sitting time or less frequent walking breaks, for improving health outcomes and healthy aging. The investigators hypothesize that frequent sit-to-stands during a 5-hour sitting period will result in health benefits that can be observed with a simple 2-minute standing interruption, and that this will be associated with improvements in metabolism and endothelial function. This pilot, 10-participant study will 1) generate preliminary data for a revised Program Project Grant application to the National Institute of Aging (NIA) that focuses on postmenopausal women, the fastest growing aged population with high life-time risk of cardiometabolic risk. This pilot study will inform sitting interruption modality design for two projects in the investigators' Program Project Grant application: "Project 1: Sedentary Behavior Interrupted: A randomized crossover treatment trial of acute effects on biomarkers of healthy aging in the laboratory (86 participants)" and "Project 2: Sedentary Behavior Interrupted: A randomized trial of 6 month effects on biomarkers of healthy aging and physical functioning in the real world (660 participants)." The current design of this pilot study is enhanced by and responsive to feedback from our initial NIA submission. This pilot study will increase our knowledge about how sedentary behavior and sitting interruption interventions influence healthy aging in postmenopausal women.

SPECIFIC AIM The deleterious health consequences of too much sitting are independent of moderate-to-vigorous physical activity. Understanding the health consequences of sitting time is particularly relevant for older adults who are extremely sedentary and at high risk of several chronic diseases that have been linked with sitting time, including type 2 diabetes. Interestingly, sedentary behavior is least studied among older adults who may benefit the most from reducing sitting time. Reducing uninterrupted sitting time in older adults is a research priority because the pervasiveness of sitting time, typically \>8 hours per day, provides many opportunities for intervention. Specific interventions are required to reduce sitting because it is such a habitual behavior and is reinforced by social norms and chair-dominant contexts.

In this pilot study, the investigators focus on three different types of prolonged sitting interruptions as variables. Studies have shown that frequent breaks in sitting may reduce risk for cardiometabolic disease. In older adults, the investigators anticipate that frequent sit-to-stand transitions will impact metabolic, inflammatory and other biomarkers, in particular those related to mitochondrial and endothelial function. A key limitation of previous sedentary intervention studies is that they have not impacted frequency of sit-to-stand transitions; rather, they decreased total sitting and increased standing time. Further, previous sedentary intervention studies have not directly compared frequent sit-to-stand transition interruptions with other interruption modalities associated with less frequent sit-to-stand transitions, for example, reduced overall sitting time (standing more) or with occasional walking breaks. The investigators propose to test these sedentary behavior interruptions modalities to disrupt prolonged sitting and explore mitochondrial- and endothelial function-based mechanisms of action. Biologic theories suggest that interrupting sitting via sit-to-stand muscle contraction and increased blood flow to extremities is key to improving in healthy aging outcomes.

In a controlled laboratory study of prolonged sitting, 3 different interruption break types will be utilized. Ten sedentary, postmenopausal participants 55+ years of age and body mass index (BMI) of 27-45 will be enrolled. After screening and enrollment, participants will visit the clinic on 4 occasions for a 6-hour monitoring period and, following a 1-hour sitting run-in period, complete each of 4 5-hour sitting protocols. The 3 sitting interruption protocols will each include sitting interruptions of different break frequency and type and will allow evaluation of the effect of sit-to-stand transitions and interruption type on acute metabolism and health outcomes. All study protocols include baseline, mid-point, and end-of-study bathroom breaks for urine sample collection with additional bathroom breaks allowed as needed. During each protocol at multiple time points, blood samples will be collected to assess changes in biomarkers of glycemic regulation (glucose and insulin areas under the curve) and mitochondrial function over the course of the sitting protocols. During each protocol at multiple time points, changes in endothelial function, specifically, blood pressure (indirect measure) and femoral flow-mediated dilation (direct measure), will be assessed. Changes in these measures will be compared between protocols. A small aliquot (0.5mL) of plasma samples and urine samples collected during the protocol will be banked for possible ancillary, exploratory studies. This study is a crossover design and each participant will be her own control. The investigators hypothesize that frequent sit-to-stands during a 5-hour sitting period will result in health benefits that can be observed with a simple 2-minute standing interruption, and that this will be associated with improvements in metabolism and endothelial function. The investigators will test this hypothesis in the following aim:

Study Aim: Using a randomized, controlled crossover study design, assess the feasibility and metabolic and endothelial function outcomes of an acute bout of prolonged sitting ± standing or walking interruptions using targeted metabolic and endothelial function biomarker analyses.