| Summary: | Background: Children are affected by disorders that have an impact on the respiratory muscles. Inspiratory muscle function can be assessed by means of the noninvasive tension–time index of the inspiratory muscles (TTImus). Our objectives were to identify the determinants of TTImus in healthy children and to report normal values of TTImus in this population. Methods: We measured weight, height, upper arm muscle area (UAMA), and TTImus in 96 children aged 6–18 years. The level and frequency of aerobic activity was assessed by questionnaire. Results: TTImus was significantly lower in male subjects (0.095 ± 0.038, mean ± SD) compared with female subjects (0.126 ± 0.056) (p = 0.002). TTImus was significantly lower in regularly exercising (0.093 ± 0.040) compared with nonexercising subjects (0.130 ± 0.053) (p < 0.001). TTImus was significantly negatively related to age (r = −0.239, p = 0.019), weight (r = −0.214, p = 0.037), height (r = −0.355, p < 0.001), and UAMA (r = −0.222, p = 0.030). Multivariate logistic regression analysis revealed that height and aerobic exercise were significantly related to TTImus independently of age, weight, and UAMA. The predictive regression equation for TTImus in male subjects was TTImus = 0.228 − 0.001 × height (cm), and in female subjects it was TTImus = 0.320 − 0.001 × height (cm) . Conclusion: Gender, age, anthropometry, skeletal muscularity, and aerobic exercise are significantly associated with indices of inspiratory muscle function in children. Normal values of TTImus in healthy children are reported. Keywords: Aerobic exercise, Children, Inspiratory muscle function, Maximal inspiratory pressure, Skeletal muscle function, Tension–time index of the inspiratory muscles
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