The ACUte effects of SITting time on physiological and psychological function in older adults (ACUSIT): An observational cohort study

Introduction: There is accumulating evidence supporting the longer-term detrimental health effects of prolonged bouts of sedentary behaviour (sitting). There is however limited data for acute doses of sitting in older adults. This study aimed to identify key physiological and psychological outcomes influenced by acute periods of inactivity. Methods: Using a randomised cross-over design, participants completed sitting times of 1, 2 and 4 hours on separate days at the same time of day, and were permitted to watch television, knit or read but not to sleep. The sitting times corresponded to a brief control period of sitting (1 hour (h)), moderately sedentary (2-4 h per day) and sedentary (>4 h per day). The primary outcome measure was lower limb power output using the Nottingham Power Rig (Watts (W)/kg). Secondary outcomes included a range of physiological and psychological measures. Assessments were made before and after each period of sitting time in a temperature-controlled room. Differences between the pre and post measurements across each session were analysed using repeated measures ANOVA with post-hoc comparisons to determine between condition differences. Results: Lower limb power output did not change significantly (p = 0.67) following the 1 h (pre: 1.44 {+/-} 0.6, post: 1.461 {+/-} 0.6 W/kg), 2 h (pre 1.42 {+/-} 0.7, post: 1.44 {+/-} 0.6 W/kg) and 4 h (pre: 1.47 {+/-} 0.7, post: 1.44 {+/-} 0.6 W/kg) sitting times. A significant increase in mean systolic and diastolic blood pressure was recorded following the 2h (systolic pre: 137 {+/-} 13, post: 141 {+/-} 6 mmHg; p<0.001; diastolic pre: 74 {+/-} 10, post 76 {+/-} 10mmHg; p<0.001) and 4 h sitting times (systolic pre 137 {+/-} 14, post 147 {+/-} 15 mmHg; p<0.001; diastolic pre 73 {+/-} 10, post 79 {+/-} 10 mmHg; p<0.001). Mean arterial pressure also significantly increased after the 2 h (pre: 95 {+/-} 10, post: 97 {+/-} 11 mmHg; p<0.001) and 4 h (pre: 95 {+/-} 10, post: 102 {+/-} 10 mmHg; p<0.001) periods of sitting. Timed Up & Go performance declined after all sessions of sitting (p=0.01) whereas Digit Symbol Substitution (DSS) scores (p=0.001) and % DSS correct scores (p<0.001) improved. Vitality declined across all sessions, but this was significantly worse after 4 h. Psychological outcome measure (Profile of Mood State; POMS) related to vigour and friendliness showed significant adverse changes across all sessions, although vigour was worst after 4 h sitting. Further, greater and negative fatigue changes were recorded after 2 and 4 h sitting compared to 1 h, with highest post-sitting values after 4 h. In a small subset of participants (n=13), significant increases in bladder volume comparing post with pre-sitting time were found across all 3 sitting periods (p<0.05), however these were not statistically significant. Conclusions: These data show that sitting for 2 h or more may have potentially deleterious effects on cardiovascular biomarkers including blood pressure, as well as increasing the risk of falling. Vitality, vigour and fatigue may also be adversely affected in older adults. These effects appear to increase with continuous sitting time.