Tomkinson GR, et al. - Here, researchers assess international and national temporal trends in the cardiorespiratory fitness (CRF) of children and adolescents and aim to investigate connections between temporal trends in CRF and temporal trends in broad socioeconomic and health-related indicators across countries. There has been a substantial decline in CRF since 1981, which is suggestive of a meaningful decline in population health. However, the international trend in CRF has not followed the anticipated trajectory, reducing and stabilising with negligible change since 2000. CRF information is required from children in low-income and middle-income countries to more confidently ascertain true international trends and figure out if temporal trends are similar to those observed in high-income and upper-middle-income countries.

Methods

• Information was obtained from a systematic search of studies that explicitly reported 20 m shuttle run test (a validated measure of CRF) descriptive information on apparently healthy individuals aged 9-17 years.
• Following the estimation of relative peak oxygen uptake (mL/kg/min) as a measure of CRF, sample-weighted temporal trends were assessed at the country-sex-age level utilizing best-fitting linear or polynomial regression models relating the year of testing to mean CRF.
• Poststratified population-weighted mean changes in absolute and percent CRF were evaluated.
• Pearson’s correlations were utilized to depict the relationship between linear temporal trends in CRF and linear temporal trends in broad socioeconomic and health-related indicators.

Results

• Utilizing information from 137 studies, temporal trends were evaluated from 9,65,264 children and adolescents from 19 high-income and upper-middle-income countries between 1981 and 2014.
• Collectively, there was a moderate decline in CRF of 3.3 mL/kg/min (95% CI -3.5 to -3.1), equivalent to a decline of 7.3% (95% CI -7.8% to -6.7%) over the 33-year time period.
• This international decline reduced with each decade and stabilised near zero around 2000.
• The decline was larger for boys than girls and was similar for children and adolescents.
• Trends also varied in magnitude and direction between countries, with most exhibiting declines.
• A strong negative association was seen between country-specific trends in income inequality (Gini index) and trends in CRF across 18 countries; meaning, countries approaching income equality had more favorable trends in CRF.