Construct Validity and Reliability of the OMNI Scale in Children and Adolescents With Neuromuscular Diseases

INTRODUCTION/AIMS: Children and adolescents with neuromuscular diseases often demonstrate muscle weakness and mobility limitations, which may increase perceived exertion during functional tasks. The OMNI scale was developed to assess perceived exertion in pediatric populations; however, its measurement properties in neuromuscular conditions remain unclear. This study aimed to examine the construct validity of the OMNI scale, using the Borg scale as a reference, and its inter-rater reliability during the 6-minute walk test (6MWT) in children and adolescents with Charcot-Marie-Tooth disease (CMT) and myopathies. METHODS: Construct validity was analyzed in 39 participants, and inter-rater reliability in 21 participants aged 4-18 years. Perceived exertion was assessed before, during, and after the 6MWT using the OMNI and Borg scales. Linear mixed-effects models examined construct validity. The intraclass correlation coefficient (ICC) and standard error of measurement (SEM) assessed reliability. RESULTS: A significant association was observed between Borg and OMNI scores (β = 0.82, p < 0.001). OMNI scores increased throughout the 6MWT, indicating changes in perceived exertion. Inter-rater reliability was moderate at the second minute (ICC = 0.67; 95% CI 0.34-0.85) and high at the end of the 6MWT (ICC = 0.75; 95% CI 0.48-0.89). The SEM was 1.74 points at the second minute and 1.32 points at the end of the 6MWT. DISCUSSION: The OMNI scale demonstrated good construct validity and acceptable inter-rater reliability, with low measurement error, supporting its clinical applicability. This suggests that the OMNI scale is a practical and reliable tool for monitoring perceived exertion in children and adolescents with neuromuscular diseases.