Is There a Curvilinear Trajectory of Motor Competence Across Different Weight Status? Exploring the Non-Linear Hypothesis in Adolescents

<b>Background:</b> Evidence supports that motor competence is inversely associated with weight status, yet less is known about this relationship among young people who are underweight. We hypothesized that there is a non-linear trajectory of motor competence across weight status categories (from underweight to obesity). <b>Purpose:</b> To check whether a non-liner relationship exists between motor competence and weight status in adolescents. <b>Research Design:</b> Cross-sectional study. <b>Study sample:</b> we assessed the motor competence of 310 participants (44.8% boys), aged 12-15 years. <b>Data Collection:</b> Motor competence was assessed the Korperkoordinationstest für Kinder (KTK). Weight status (underweight, normal weight, overweight and obesity) was determined using body mass index (BMI). <b>Results:</b> Motor competence was inversely associated with BMI in normal weight (rho = -.222, <i>p</i> = .001), overweight (rho = -.309, <i>p</i> = .028) and obesity (rho = -.663, <i>p</i> < .001), but not in underweight (rho = .193, <i>p</i> = .508). Adolescents with normal weight presented higher motor competence than those with overweight (mean difference = 17.198, <i>p</i> = .001) and obesity (mean difference = 31.686, <i>p</i> < .001). There was no significant difference in motor competence between normal weight and underweight categories. In addition, boys showed a curvilinear trajectory of motor competence, being ascendant from underweight to normal weight and then downward with increasing BMI. Polynomial regressions, fitting a non-linear model, confirmed a non-linear relationship between motor competence and BMI in boys (B = -3.534, <i>p</i> < .001). <b>Conclusions:</b> Our findings suggest that the inverse relationship between motor competence and BMI does not occur in adolescents who are underweight. Furthermore, our results supported the non-linear hypothesis about the relationship between motor competence and weight status in boys.