Human-Centered Product–Interior Design Optimization: Linking Adjustable Furniture, Indoor Environmental Quality, and User Comfort in Small Workspaces

Small workspaces function as integrated systems, yet ergonomic furniture and indoor environmental conditions are typically evaluated in isolation. This study investigates the independent and combined impacts of adjustable furniture and optimized indoor environmental quality (IEQ) on user comfort, physical well-being, and work performance. We conducted a multicenter, assessor-blinded 2 × 2 factorial controlled trial across six office sites involving 240 participants. Subjects were equally assigned to a four-week intervention of fixed furniture with basic IEQ, adjustable furniture with basic IEQ, fixed furniture with optimized IEQ, or an integrated condition featuring both. The furniture intervention utilized individually configured sit-stand desks, while IEQ optimization targeted precise thermal, ventilation, lighting, acoustic, and particulate metrics. At week four, the integrated condition yielded the highest overall comfort scores (5.62 ± 0.53), significantly outperforming the fixed-basic baseline (3.99 ± 0.60). Analysis revealed a positive interaction between the two interventions. Adjustable furniture distinctly enhanced anthropometric fit and posture comfort while reducing neck and lower-back discomfort. Conversely, optimized IEQ primarily improved environmental comfort, task speed, perceived productivity, and mitigated mental fatigue. The integrated approach provided additive benefits for task accuracy and workspace satisfaction, although neither intervention significantly altered creativity. These findings demonstrate that physical adjustability and environmental quality address distinct, complementary facets of the occupational experience. Ultimately, human-centered workspace design must transcend isolated component selection, synergistically combining individual workstation fit with comprehensive IEQ management to maximize occupant comfort and functional performance.