Abstract P136: Low Cardiorespiratory Fitness Among US Adolescents: Prevalence, Correlates, and Association with Adiposity Markers- Findings from the 1999-2004 National Health and Nutrition Survey
Authors: Johnson Jonetta L , Norris Jeffrey L , Pratt Michael , Lobelo Felipe 
Published: July 2021

Introduction.
Cardiorespiratory fitness (CRF) is a powerful marker of current of CVD risk among youth. The goals of this study are to describe the prevalence of low CRF among US adolescents aged 12-19 years (N=4,955), determine its sociodemographic and physical activity (PA) behavioral correlates and explore its association with adiposity markers. We hypothesize some PA variables will be significantly associated with low CRF after controlling for adiposity and other confounders.

Methods.
Data from three rounds of NHANES from 1999-2004, the most recent nationally representative data available on CRF, were analyzed. CRF was estimated as maximal oxygen uptake via measured heart rate responses to a treadmill test and categorized as healthy or low based on CVD-validated FITNESSGRAM standards. The prevalence of low CRF across various sociodemographic and PA behavioral indicators were calculated in analyses stratified by gender. Chi-square or linear trend analyses were used to calculate differences across groups. BMI groups (normal vs. overweight/obese) and WC groups (high vs. normal) were coded for CRF-adiposity cross-tabulations. High WC was classified as ≥90
th
age, gender and race-specific percentile for 12-18 year olds and >94 cm and >80 cm for 19 year olds males and females, respectively. Correlates of low CRF were examined using multivariable logistic regression models. All analyses were conducted in SUDAAN to account for the survey’s complex sampling design.

Results
. Overall 37% of US adolescents had low CRF. The prevalence of low CRF was higher in females (38.6%) than males (35.1%) (p=0.04) but did not differ across racial/ethnic or poverty-to-income ratio groups. There were significant bivariate associations between low CRF and self-reported active commuting (p<0.02), <2 hours/day screen time (p<0.001), higher MET-min/d of moderate-to-vigorous (p<0.001) and vigorous (p=0.001) PA. Among boys and girls, the prevalence of low CRF was lower among those normal weight (25.9%; 32.4%) vs. those overweight (42.3%; 46.9%) or obese (66.3%; 56%) (p for trend<0.001). Similarly the prevalence of low CRF was lower among those with normal (29.4%; 35%) vs. high WC (76.8%; 53.8%). Adolescents who did not actively commute via biking or walking were more likely to have low CRF compared to those who were active commuters (OR=1.39; 95% CI 1.00-1.93; p=0.05 for girls) and (OR:1.49; 95% CI 1.06-2.10; p=0.02 for boys). Similarly, among boys and girls, those who used ≥2hours/day screen-time were more likely to be low fit (p≤0.02).

Conclusion
. A significant portion (50-30%) of adolescents with high BMI or WC exhibit normal CRF while about 1 in 4 normal weight adolescents have low CRF and are at increased CVD risk. Promotion of PA among adolescents to improve CRF could help both normal weight and overweight adolescents with low CRF improve their CRF and lower CVD risk independently of adiposity.