Intensity of physical activity, cardiorespiratory fitness, and body mass index in youth.
BACKGROUND
The purpose of this study was to analyze the relation between body mass index (BMI), Cardiorespiratory Fitness (CRF), and levels of physical activity (PA) from sedentary to very vigorous intensities, measured by accelerometry, in students from a middle and high school.


METHODS
This cross-sectional study included 111 children and adolescents, age 11 to 18 years. PA was assessed with an accelerometer for 7 consecutive days (1 minute epoch) using specific cut-points. PA components were derived using special written software (MAHUffe). CRF was assessed by maximal multistage 20m shuttle run. T-test was used to test differences between BMI groups, Pearson's correlation, to analyze correlations between all variables and multinomial logistic regression, and to predict the value of BMI categories.


RESULTS
This paper provides evidence that BMI was inversely and significantly correlated with CRF. Only CRF was correlated with Vigorous and Very Vigorous PA levels and total amount of PA. Children with Overweight/Obesity were less likely to perform more laps than normal weight counterparts. The total amount or intensity level of PA did not show any influence on BMI level.


CONCLUSIONS
Low CRF is strongly associated with obesity, which highlights the importance of increasing CRF for a protective effect even in youth. No associations were found for PA and BMI.
Research Centre in Physical Activity Health and Leisure, FADE-UP, Porto, Portugal.
Luisa
L
Aires
Pedro
P
Silva
Gustavo
G
Silva
Maria Paula
MP
Santos
José Carlos
JC
Ribeiro
Jorge
J
Mota
D000054:Acceleration; D000293:Adolescent; D001823:Body Composition; D015992:Body Mass Index; D002320:Cardiovascular Physiological Phenomena; D002648:Child; D016001:Confidence Intervals; D003430:Cross-Sectional Studies; D005260:Female; D006304:Health Status; D006305:Health Status Indicators; D006801:Humans; D016015:Logistic Models; D008297:Male; D009043:Motor Activity; D015999:Multivariate Analysis; D009765:Obesity / Q000453:epidemiology*; D016017:Odds Ratio; D050177:Overweight / Q000453:epidemiology; D010809:Physical Fitness; D011174:Portugal / Q000453:epidemiology; D012143:Respiratory Physiological Phenomena; D012307:Risk Factors; D057185:Sedentary Behavior