## 1 Introduction  
Falls among the elderly represent a significant public health concern with substantial consequences. Falls can have a devastating impact on the lives of older adults, leading to injuries, immobility, activity limitations, placement in nursing homes, health deterioration, and increased risk of mortality [1]. Research indicated that nearly all hip fractures in older adults result from falls [2], with a significant percentage leading to serious outcomes such as long-term institutionalization or death. In addition, there can also be psychosocial consequences such as the fear of falling again, increased healthcare costs, strain on family relationships, and limited social participation [3]. The costs associated with fall-related injuries are substantial. In the United States, healthcare expenses for fall-related injuries among older adults were approximately 50 billion dollars annually [4]. Additionally, as the elderly population grows, the incidence of non-fatal falls has risen significantly, increasing demand for emergency and healthcare services [4]. In 2018 alone, an estimated 3 million emergency department visits, over 950,000 hospital admissions or transfers to other facilities (e.g., trauma centers), and around 32,000 deaths were attributed to fall-related injuries among older adults [4]. Maintaining postural balance is essential for mobility, independence, and quality of life in older adults. Continuous monitoring of balance is, therefore, crucial to identify situations that may lead to increased fall risk, such that we can put preventive interventions in place before it happens. Balance assessment methods have evolved significantly over time, ranging from simple clinical observations to more advanced technological approaches. Traditional methods for evaluating balance include clinical assessments performed by misotherapists, which involve observation of gait, posture, behavior, facial expressions, and emotional responses [5]. Traditional methods may also include functional tests such as the six-minute walk test [6], the Timed Up and Go (TUG) test [7], the Berg Balance Scale (BBS) test [8], and the Star Excursion Balance Test (SEBT) [9]. Each one was designed to evaluate different aspects of balance and mobility. However, clinical observation faces inherent limitations due to its subjective nature. Inter-observer variability is a major challenge, potentially impacting the reliability of assessments [10]. As demonstrated in a previous study using SEBT [9], there were disagreements among clinicians in identifying movement abnormalities. Despite their practicality and simplicity, these functional tests still lacked the precision and objectivity offered by more advanced techniques involving direct measurements. The more advanced quantitative techniques that were developed and validated are force platforms [11] and motion capture systems [12] for estimating the center of pressure or mass. Force platforms have been used to measure postural sway and center of pressure movements during quiet standing and various balance tasks [11]. Motion capture systems include marker-based optical systems and markerless video-based systems, which allow for detailed analysis of body movements. Nevertheless, both clinical observations and advanced technologies primarily operate within controlled clinical environments. These methods are constrained in their ability to capture the dynamic nature of balance in real-world scenarios. Specifically, previous research highlighted a critical issue that force plate measures often exhibit a limited correlation with actual balance performance outside the laboratory [11]. Recognizing this limitation underscores the need for assessment tools that offer greater ecological validity, capable of providing metrics for postural balance assessment in everyday life situations. Considering this limitation, wearable devices that can capture similar measures may be more appropriate.