Reliability and validity of the force intersection point in the assessment of human quiet standing balance

Background: This study evaluated psychometric properties of the Intersection Point Height, derived from ground-on-feet force characteristics, as a tool for assessing balance control. We compare this metric with traditional center of pressure (CP) measurements. Methods: Data from a public dataset of 146 participants, divided into younger (<60 years old) and older (>= 60 years old) adults, were analyzed. Clinical tests included the Short Falls Efficacy ScaleInternational, International Physical Activity Questionnaire-Short Form, Trail Making Tests A and B, and the Mini-Balance Evaluation Systems Test. Reliability and validity were assessed through the intra-class correlation coefficient (ICC[3,1]) for mean Intersection Point Height in each test condition and Spearman's rho between summative Intersection Point Height (the sum of intra-condition mean values across all test conditions within one subject) and other variables of interest, respectively. Findings: Mean Intersection Point Height showed good to excellent reliability (ICC = 0.712-0.901), similar to that of CP velocity (ICC = 0.733-0.922) and greater than that of variance CPx (0.475-0.768). Summative Intersection Point Height exhibited strong convergent validity with Trail Making Tests A and B (rho = 0.49, p < 0.001) and the Mini-Balance Evaluation Systems Test (rho = -0.47, p < 0.001). At most, a weak to moderate association (rho = 0.39-0.49, p < 0.001) was found between intra-condition mean Intersection Point Height with CP metrics. Intra-condition mean Intersection Point Height demonstrated weak to moderate convergent validity with several clinical measures (rho = 0.32-0.52, p < 0.001). In contrast, at most, a weak to moderate association (rho = 0.39-0.49, p < 0.001) was found between intra-condition mean Intersection Point Height with CP metrics. Interpretation: The Intersection Point Height is a reliable and valid balance measure. Further, we believe that it is a more comprehensive evaluation than CP metrics.