Test–Retest Reliability, Parallel Test Reliability, and Internal Consistency of Balance Assessments in Young Healthy Adults

<b>Objectives:</b> An objective evaluation of balance abilities is crucial in research, rehabilitation, sport, and daily life. With ongoing technical advancements, the number of innovative evaluation tools is continuously increasing. This study assessed the methodological quality of various differential balance assessments in young, healthy adults. <b>Methods:</b> Two technically sophisticated balance assessments using a force plate (Single-Leg Landing Test, Single-Leg Squat Test) and a conventional balance assessment using a simple test kit (Y-Balance Test) were applied to 42 students at two different time points. Test-retest reliability, parallel test reliability, and internal consistency were evaluated for each test and item. <b>Results:</b> All tests and (almost) all items showed excellent to acceptable test-retest reliability. In all tests, internal consistency was detected for only some items, while the other items were internally inconsistent. Only a small proportion of tests and/or their items demonstrated acceptable parallel test reliability. The balance performance of the right and left legs showed excellent or good reliability for each item. <b>Conclusions:</b> Significant test-retest reliability and consistency between right and left leg performance suggest good methodological quality of the assessments. The lack of parallel test consistency aligns with previous studies that emphasise the multi-faceted nature of balance tasks, suggesting that balance ability is task-specific rather than a "general ability". Future studies should investigate and compare the biological and neural backgrounds of differential balance tasks to provide further insights into this topic.