Modeling the dose–response rate/associations between VO _2max and self-reported Physical Activity Questionnaire in children and adolescents

Background: This study sought to explore the dose–response rate/association between aerobic fitness (VO _2max) and self-reported physical activity (PA) and to assess whether this association varies by sex, age and weight status. Methods: VO _2max was assessed using the 20-m shuttle-run test. PA was assessed using the Physical Activity Questionnaire (PAQ) for Adolescents (aged >11 years, PAQ-A) or for Children (aged ≤11 years, PAQ-C). The associations between VO _2max and PAQ were analyzed using analysis of covariance (ANCOVA), adopting PAQ and PAQ ² as covariates but allowing the intercepts and slope parameters of PAQ and PAQ ² to vary with the categorical variables sex, age group, and weight status. Results: ANCOVA identified a curvilinear association between VO _2max and PAQ, with positive linear PAQ terms that varied for both sex and weight status but with a negative PAQ ² term of -0.39 (95% confidence interval (CI): –0.57 to –0.21) that was common for all groups in regard to age, sex, and weight status. These curvilinear (inverted U) associations suggest that the benefits of increasing PA (same dose) on VO _2max is greater when children report lower levels of PA compared to children who report higher levels of PA. These dose–response rates were also steeper for boys and were steeper for lean children compared to overweight/obese children. Conclusion: Health practitioners should be aware that encouraging greater PA (same dose) in inactive and underweight children will result in greater gains in VO _2max (response) compared with their active and overweight/obese counterparts.