Within-Session Reductions in Negative Mood During a 4-Week Upright Sitting Practice in Japanese Young Adults: An Exploratory Observational Study.

OBJECTIVES: This exploratory study examined changes in stress-related indicators, including subjective mood states, autonomic nervous system activity, and salivary biomarkers, during a 4-week period in which healthy young adults performed an instructed upright sitting posture. DESIGN: This study employed a single-arm, within-subject, repeated-measures observational design. MATERIALS AND METHODS: Eighteen healthy university students (10 males and 8 females) completed a 4-week upright sitting posture practice. Assessments took place at baseline (Week 0), mid-practice (Week 2), and end-of-practice (Week 4). At each visit, participants underwent a 10-minute seated rest; pre-session assessments using the Profile of Mood States, Second Edition (POMS2), autonomic indices, and salivary biomarkers; a 5-minute upright sitting period; and post-session assessments. Autonomic activity was indexed by heart rate (HR) and heart rate variability (HRV), and salivary cortisol, chromogranin A, oxytocin, and α-amylase were measured. RESULTS: Across assessment weeks, sessions that included the instructed upright sitting posture were accompanied by within-session pre-post improvements in most POMS2 mood indices, with large effects for several negative mood subscales and Total Mood Disturbance. Significant main effects of Week were observed for Confusion-Bewilderment, Tension-Anxiety, and Total Mood Disturbance, whereas other mood indices did not show consistent change. HR showed significant main effects of Measurement Timing and Week, while HRV indices and salivary biomarkers did not show consistent or statistically significant patterns. At Week 4, comfortable maintenance time-the self-reported maximum duration participants felt they could maintain the instructed posture-was positively associated with total practice time; this association was considered hypothesis-generating.