# The Impact of Cell Phone Usage on Fall Risk and Postural Control During Free-Standing
## 1 Introduction  
Postural control is a key biomechanical mechanism that enables humans to maintain stability and balance in static and dynamic situations [1]. It depends on the intricate cooperation of the visual, vestibular, and proprioceptive systems, whose synchronization is essential for the body to respond quickly and accurately to changing environmental conditions [2]. Postural control is typically assessed using specialized tools such as force platforms, which record changes in the displacement of the center of pressure (CoP) of the feet on the ground. These measurements enable the analysis of body-movement variability in the anterior-posterior (AP) and mediolateral (ML) directions, serving as important indicators of postural stability. By analyzing the variability of the CoP trajectory, it is possible to monitor the effectiveness of the mechanisms responsible for maintaining balance [3]. Linear indicators such as the CoP sway range, CoP velocity, and the ellipse sway area are often used to quantify body sway. However, these linear measures alone cannot fully capture the complexity of dynamic postural sway. [PERSON] and [PERSON] [4] emphasize the importance of nonlinear measures when analyzing CoP signals, particularly concerning temporal variations in CoP displacement across the AP and ML directions. These nonlinear metrics provide insight into the regularity, adaptability, stability, andcomplexity of the postural control system. One widely used nonlinear metric is sample entropy (SampEn), which assesses the regularity of the CoP time series. Higher SampEn values reflect a more irregular CoP time series, indicative of a healthy and adaptive system, while lower values suggest greater regularity, which may signal rigidity and potential pathology [5]. Another nonlinear measure, fractal dimension (FD), evaluates the complexity of the CoP signal. An FD value of 1 would theoretically represent an entirely still stance, which is practically impossible due to natural postural sway [6]. Finally, the Lyapunov exponent (LyE) measures the system's resistance to external perturbations. A higher LyE value indicates greater adaptability and faster response to stimuli, whereas a lower LyE suggests difficulties in adjusting to environmental changes and potential rigidity in the system [7]. Fall risk is closely linked to the body's dynamic and static stability, which determine the ability to maintain balance under different conditions [8]. Static stability refers to the body's ability to maintain equilibrium at rest, whereas dynamic stability refers to movement control and the ability to restore equilibrium after disturbances [9]. The two aspects are interrelated--better static stability promotes a more effective response to changes in position, which influences dynamic stability. In the context of fall risk, static instability can lead to difficulty maintaining a standing position without additional support. At the same time, impaired dynamic stability can result in problems with movement control, especially during sudden changes in direction, braking, or moving over uneven ground. Research has shown that people prone to falls have poorer dynamic stability compared to healthy individuals of a similar age and younger adults [10]. The relationship between fall risk and static/dynamic stability requires further clarification. While both aspects contribute to balance control, their distinct roles and interplay in increasing fall susceptibility remain an area of ongoing investigation. Providing additional explanations in the introduction would enhance the reader's understanding by outlining how different stability components contribute to fall risk. Furthermore, external factors such as environmental conditions (e.g., slippery pavement and uneven ground) and cognitive load due to dual-tasking influence the risk of falling [11; 12]. Using the phone while walking, talking, or having to focus on another task at the same time can impair balance control, as attention resources are split between different activities.