The importance of body mass normalisation for ultrasound measurement of the transversus abdominis muscle: The effect of age, gender and sport practice.

BACKGROUND: Some studies have not considered body mass as a confounder in TrA analysis, which may have led to improper interpretation of results.

OBJECTIVES: To assess the differences in the effect of age, gender and physical activity between normalised for body mass and actual values of the TrA as well as to establish the effect of age, gender and physical activity on normalised for body mass TrA thickness in adolescents.

DESIGN: The study was a cross-sectional study conducted at selected primary and secondary schools, and colleges in the Silesian region of Poland.

METHOD: A real-time ultrasound was used to obtain images of the TrA muscle. Body mass normalisation for TrA thickness was performed with allometric scaling and the following equation: Allometric-scaled TrA = TrA thickness/body mass0.61 .

RESULTS: Analysis has shown that boys have significantly thicker muscle by 0.27 mm (95% CI 0.04-0.50) than girls, and those who practise sports have thicker muscle by 0.30 mm (95% CI 0.06-0.52) than non-active individuals. For allometric-scaled TrA, there were no significant effects (p > 0.50). There was a significant correlation between participants age and the actual value of the TrA (r = 0.42, p < 0.05). The correlation between age and allometric-scaled TrA was insignificant and close to zero (r = -0.006, p = 0.93).

CONCLUSIONS: An analysis of TrA thickness without body mass normalisation can deliver improper interpretation of study results. Thus, it is recommended in future researches to analyse TrA thickness measurement after normalisation rather than actual values. In the adolescent population, there is no effect of gender, age and physical activity on allometric-scaled TrA thickness.