## 1 Introduction  
Sedentary behavior has become a dominant feature of modern life, encompassing occupational, educational, and recreational activities. With increased screen time and desk-based work, individuals now spend much of their day seated, contributing to a range of musculoskeletal issues. Office workers, in particular, often sit for over seven hours daily, a behavior strongly associated with neck, shoulder, and lower back discomfort [1, 2, 3]. Epidemiological evidence links prolonged sitting--especially when exceeding half the workday--to a heightened risk of chronic low back pain [4]. Biomechanically, extended sitting can reduce spine-stabilizing muscle activity, leading to spinal fatigue and postural deconditioning [5]. Recent studies have reinforced these risks, particularly among individuals engaged in remote or screen-based work. For instance, [PERSON] et al. [6] reportedstrong associations between sedentary behavior and neck pain in frequent users of mobile devices, while [PERSON] et al. [7] identified extended sitting during work-from-home settings as a predictor of neck and back symptoms. Despite decades of ergonomic research, consensus on optimal sitting posture remains elusive. Recommendations like \"sit up straight\" often reflect cultural norms rather than biomechanical evidence [8]. While squohed or flexed postures are commonly linked to spinal discomfort [9], they are frequently observed in everyday settings [10; 11]. Habitual postures typically involve mid-range trunk flexion and are more flexed than postures perceived as \"correct\" or \"ideal\" [12; 13]. In contrast, upright postures often promoted by clinicians require increased muscle activity, which may reduce postural sustainability due to fatigue [14; 15]. Importantly, there is limited empirical evidence linking any one posture to reduced spinal load or improved musculoskeletal outcomes [16; 17]. Furthermore, the shift from paper-based to digital work is seen as a key contributor to musculoskeletal disorders, highlighting the need for ergonomic adaptations in workplace design [18]. Beyond debates over ideal posture, prolonged maintenance of any static posture--whether upright, squohed, kyphotic, or lordotic--can cause discomfort or injury [19]. This has led to growing interest in postural variability as a protective factor. People naturally adjust their posture over time to redistribute load and maintain comfort, yet it remains unclear how consistently they can reproduce specific postures under identical conditions. Interventions that promote movement, such as sit-stand desks or posture change reminders, have been shown to reduce discomfort without negatively affecting productivity [20]. Chair design plays a critical role in influencing sitting behavior. Features such as adjustability, contouring, and back support can either facilitate or restrict postural movement. However, individual responses to different chair designs vary widely, and the underlying mechanisms that drive posture selection remain incompletely understood [21]. To evaluate seating comfort, researchers have employed multiple methodological approaches. Subjective questionnaires are commonly used to assess perceived comfort, discomfort intensity, and user preferences under varying tasks or seating conditions [22; 23; 24; 25]. Anthropometric studies have examined how body dimensions affect seat fit, contact pressure, and support adequacy across diverse populations [26; 27; 28]. Pressure mapping has been applied to quantify interface pressure distribution, identify high-pressure zones, and explore their associations with perceived comfort and load-related risks [29; 30; 31]. More recently, direct measurement of joint angles has emerged as a reliable method for objectively quantifying seated posture and musculoskeletal loading [32]. In line with these developments, modern ergonomic design increasingly emphasizes dynamic sitting--promoting movement and postural variation--over static postures traditionally regarded as ideal [33]. A foundational study by [PERSON] et al.