Lu KD; Bar-Yoseph R; Radom-Aizik S; Cooper DM.

Scandinavian Journal of Medicine & Science in Sports. 29(9):1392-1401,
2019 Sep.

INTRODUCTION: Physical activity and fitness are essential for healthy
growth in children. The National Health and Nutrition Examination Survey
(NHANES) evaluated fitness by estimating VO2 max from submaximal
measurements of heart rate (HR) during graded treadmill exercise. Our aims
were (a) to examine how well NHANES methodology used to estimate VO2 max
correlated with actual VO2 max and (b) to evaluate a novel fitness metric
using actual data collected during exercise and its relationship to
physical activity and sedentary time, lipid profiles, and body
composition.

METHODS: Fifty-three adolescents completed NHANES submaximal exercise
protocol and maximal graded cardiopulmonary exercise testing. We used a
novel approach to quantifying fitness (DELTAvelocity x incline x body mass
(VIM)/DELTAHR slopes) and evaluated its relationship to physical activity
and sedentary time using NHANES data (n = 4498). In a subset (n = 740), we
compared DELTAVIM/DELTAHR slopes to NHANES estimated VO2 max and examined
their relationship to cardiovascular risk factors (BMI percentiles and
lipid levels).

RESULTS: Measured VO2 peak was moderately correlated with NHANES
estimated VO2 max (r = 0.53, P < 0.01). Significantly higher
DELTAVIM/DELTAHR slopes were associated with increased physical activity
and decreased sedentary time. DELTAVIM/DELTAHR slopes were negatively
associated with LDL, triglycerides, and BMI percentiles (P < 0.01). In
general, the two fitness models were similar; however, DELTAVIM/DELTAHR
was more discriminating than NHANES in quantifying the relationship
between fitness and LDL levels.

CONCLUSION: We found that the NHANES estimated VO2 max accounted for
approximately 28% of the variability in the measured VO2 peak. Our
approach to estimating fitness (DELTAVIM/DELTAHR slopes) using actual data
provided similar relationships to lipid levels. We suggest that fitness
measurements based on actually measured data may produce more accurate
assessments of fitness and, ultimately, better approaches linking exercise
to health in children.