Reference values and secular trends for cardiorespiratory fitness in children and adolescents with obesity.

Aim: To present specific reference values for cardiorespiratory fitness (CRF) in children with obesity and to analyse secular trends of CRF in the studied population.

Methods: Cardiorespiratory fitness, the maximal oxygen uptake (VO max), was estimated with the Åstrand-Rhyming submaximal bicycle test, in 705 Swedish children (356 girls, 8-20 years) with obesity according to the International Obesity Task Force (IOTF). Data were collected from 1999 to 2013. Secular trends, analysed with multiple linear regression, were adjusted for age, height and body mass index standard deviation score (BMI SDS).

Results: All children had low CRF compared with normal weight standards but there was a marked variability of CRF in children with obesity, which was possible to quantify with the developed obesity specific CRF reference values. The mean value of absolute VO max (L/min) increased with age and relative VO max (mL/kg/min) decreased with age in both boys and girls. There was a negative secular trend in both sexes (P < .001).

Conclusion: These are the first obesity specific reference values of CRF in children enabling clinical evaluation in childhood obesity treatment. Cardiorespiratory fitness in children with obesity has declined the last decades, indicating that also within this vulnerable group physical activity has gone down.