Reproducibility of Proprioceptive Performance in Institutionalized Older Adults Using a Smartphone-Based Joint Position Sense Test

<b>Background:</b> Joint position sense (JPS) is a critical component of proprioception and postural control, especially in older adults, where deficits are associated with increased risk of falls and functional decline. Recent studies have explored smartphone-based digital inclinometers as accessible tools for clinical proprioceptive assessment, but their participant-level reproducibility in institutionalized elderly populations remains unexplored. <b>Objective:</b> We aimed to examine the reproducibility of joint position sense performance in institutionalized older adults, using a smartphone-based inclinometer that has been applied in other populations. Assessing joint position sense with accessible smartphone-based tools may provide practical insights for rehabilitation and functional assessment in older adults. <b>Methods:</b> Thirty-five-year-old or older adults (mean age 85.9 ± 8.19 years) participated in this test-retest study. JPS was assessed using the iPhone^® inclinometer. Participants memorized and attempted to reproduce a 30° forward trunk flexion while standing. The absolute angular error was measured across two sessions, one week apart. Relative and absolute reproducibility were analyzed using intraclass correlation coefficients (ICC 2,1), standard error of measurement (SEM), Smallest Real Difference (SRD), and Bland-Altman analysis. <b>Results:</b> The ICC for the whole sample was 0.839 (95% CI: 0.72-0.91), indicating good reproducibility of participants' proprioceptive performance. SEM and SRD were 3.65° (33.3%) and 10.1° (92.3%), respectively. Bland-Altman plots showed minimal bias (0.23°) and only 5.71% of values fell outside the 95% limits of agreement. <b>Conclusions:</b> Participants demonstrated moderate-to-good reproducibility in replicating joint position sense, reflecting consistent proprioceptive performance across sessions. This approach demonstrates feasibility for repeated proprioceptive assessment in this population. These findings have potential applications for functional monitoring and fall-prevention programs in institutionalized older adults.