Locomotive syndrome (LS) is a condition proposed by the Japanese Orthopaedic Association that describes reduced mobility due to impairment of the locomotive organs [1]. Although studies initially focused on elderly people, recent observations have suggested that early signs of locomotive dysfunction may also be present in children [2]. This suggestion aligns with trends concerning children's physical fitness and motor function. A comprehensive survey that analyzed global trends in children's physical performance between 1981 and 2014 revealed a substantial decline in physical performance across many countries worldwide [3]. Early detection of motor function issues in children is crucial because it can lead to timely interventions, potentially preventing long-term health problems and improving overall quality of life. Moreover, understanding motor function in childhood may provide insights into the developmental trajectory of locomotive abilities, informing preventive strategies for LS in adulthood.

To address this, the term ‘Kodomo Locomo’ (LS in Children) was proposed, and a four-item check was formulated to assess it [4]. However, the validity of this check in accurately assessing children's motor abilities has been questioned. In one study, among 285 participants, 115 (40.4 %) were diagnosed with LS [5]. Notably, of these 115 children with LS, 46 (40.0 %) were identified solely based on their inability to perform the forward flexion test. This high proportion of cases determined by a single test item suggests that the proposed Kodomo Locomo check items may lack adequate validation and might not comprehensively assess children's motor abilities.

The Stand-Up Test is a standard assessment for diagnosing LS in adults and has shown promise in evaluating overall motor function [6,7]. There are single-leg and double-leg versions. However, applying this test and criterion directly to children is challenging due to their developmental stages and physical capabilities. For children, we suggest that the single-leg version of the Stand-Up Test is more appropriate, as the double-leg version is generally too easy to perform, meaning it is not sufficiently discriminative.

For the purposes of this study, we therefore focused on adapting the Single-Leg Stand-Up Test (SLSUT) for children. This adaptation may provide insights into children's motor function and could be especially suitable for their developmental stages. The primary aim of this study is to evaluate the effectiveness of both the Kodomo Locomo check and the SLSUT in assessing motor function in children. We compare the results of these tests with the standardized New Physical Fitness Test, which serves as an established measure of children's physical abilities [8]. We hypothesize that the SLSUT will have significant correlation with the New Physical Fitness Test, which would suggest their potential utility in assessing children's motor function. We also aim to explore whether the SLSUT offers any unique advantages in evaluating specific aspects of motor abilities in children compared with the Kodomo Locomo check. We seek to contribute to the development of simple yet effective tools for assessing motor function in children, potentially aiding in the early detection and prevention of locomotive issues.