Effects of Cardiorespiratory Fitness Over Cardiovascular Risk Factors Controlling for Objectively Measured Physical Activity in Youths

Introduction This study aimed to verify the effects of cardiorespiratory fitness levels over a set of cardiovascular risk factors, controlling for sex and physical activity (PA) of moderate (MPA), vigorous (VPA) and very vigorous (VVPA) intensities in children and adolescents.

Methods Students aged 10-19 years (51 boys and 90 girls) completed measurements to participate in the study. Measured cardiovascular risk factors were: waist circumference (WC), body mass index (BMI), total cholesterol (TC), high-density cholesterol (HDL), low-density cholesterol (LDL), triglycerides (TRI), fasting glucose (GLU), systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP). A metabolic syndrome risk score (MRS) was computed from the standardized z-score of WC, HDL, TRI, GLU and MAP. The 20-meter shuttle run test (SR) was used to assess CRF. FITNESSGRAM reference standards for SR laps were considered to classify participants in low-fit and fit. PA was measured by accelerometers (7164 MTI, Actigraph) during 7 consecutive days. PA was expressed as the time (min/day) expended in MPA (2000-2999 counts/min), VPA (3000-4499 counts/min) and VVPA (>4500 counts/min). A Multivariate Analysis of Covariance (MANCOVA) was used assuming CRF levels as the independent factor. Cardiovascular risk factors and MRS were assumed as dependent variables. Sex, MPA, VPA and VVPA were included in the model as covariates. Analyses were carried out in SPSS 19.0 with a significance level set at 0.05.

Results A preliminary analysis indicated that there were no significant interactions between factors and covariates. For the definitive model, the strength of the relationship between CRF levels and the set of cardiovascular risk factors was strong (multivariate ?2 >0,25). Forty four percent of the variance in cardiovascular risk factors is accounted for differences in CRF levels, holding constant sex and PA. Sex differences explained 18,6% of the variance in dependent variables, controlling for the differences in CRF and PA. Only VPA showed a significant effect.

Conclusions Results indicate that CRF levels have a significant effect over a set o cardiovascular risk factors, independent of sex and PA. Furthermore, VPA also has a significant effect over cardiovascular risk factors, independent of sex and CRF levels. This study was supported by FCT (Projects: PTDC-DES-7242-2006 and PTDC/DES/099018/2008; PhD grant: SFRH/BD/45090/2008).