ANATOMICAL AND ERGONOMIC EVALUATION OF ZERO GRAVITY POSITION IN RECLINER AND SOFA DESIGN

Abstract

This study examines the anatomical and physiological validity of Zero Gravity (ZG) positioning in recliners and sofas by integrating findings from biomedical engineering, industrial design, and recovery science. Using established benchmarks specifically, the 128° trunk-to-thigh and 133° thigh-to-calf angles, 25 recliner models from 10 internationally recognized brands were assessed for alignment with NASA’s Neutral Body Posture. The methodology included a mixed-methods approach: biometric testing was conducted on 150 participants, split between a ZG group and a matched control group using conventional recliners. Physiological data were captured using cardiovascular, musculoskeletal, and respiratory metrics, while subjective responses were gathered using validated ergonomic instruments including the Nordic Musculoskeletal Questionnaire, Oswestry Disability Index, and Borg CR10 Scale. These tools ensured reduced response bias and strengthened the internal validity of findings.  Results indicated that only 28% of the tested recliners met anatomical ZG criteria. Models adhering to ZG alignment demonstrated significantly improved outcomes, including lower spinal loading, increased blood circulation, enhanced breathing efficiency, and higher overall comfort. ANOVA and multiple linear regression analyses identified spinal alignment and muscle relaxation as strong, statistically significant predictors of perceived comfort. Participants consistently reported greater satisfaction with recliners that precisely mirrored NASA’s recommended posture. This study emphasizes that the 'Zero Gravity' label should reflect objective ergonomic criteria, not subjective branding. By offering a replicable framework for product validation, this research bridges the gap between clinical science and commercial design, supporting innovation in health-focused seating solutions.