Temporal trends in the cardiorespiratory fitness of children and adolescents representing 19 high income and upper middle-income countries between 1981 and 2014
Source: British Journal of Sports Medicine Online First
Authors: Grant R Tomkinson, Justin J Lang, Mark S Tremblay
Commentary by Natasha Schranz, Co-Chair Active Healthy Kids Australia, University of South Australia
We know that a person’s level of cardiorespiratory fitness (CRF), or the ability of their body to supply fuel and oxygen to the working muscles during sustained physical activity, is an indicator of good health. We also know that CRF is the fourth leading risk factor for cardiovascular disease and it has been shown that low CRF in late adolescence is significantly linked with all-cause mortality in adulthood. The long-standing thought (of most) is that the children of today are less ‘fit’ than their parents and this suggests we are in a spot of trouble with regards to the health and wellbeing of our next generation.
This paper looks to unpack this long-standing thought by examining international and national temporal trends in the CRF of children and adolescents from high- and upper middle-income countries spanning 1981 to 2014. After a systematic search of the literature 20 m shuttle run test data from 137 studies, representing 956,264 participants aged 9-17 years from 19 countries, were included in analyses to produce temporal trends at the country–sex–age level with the change in mean CRF (absolute and per cent) per year reported. Correlations between temporal trends in CRF and temporal trends in percentage overweight/obese, percentage physically active and Gini index (income equality/inequality) across countries were also examined.
International temporal trends show that between 1981 and 2014 there was in fact a moderate decline in CRF (–3.3mL/kg/min or –7.3%) however the rate of decline from 1981 is seen to be slowing up until 2000 (–2.2 mL/kg/min and –1.6 mL/kg/min per decade in 1980s and 1990s respectively) at which point the decline in CRF stabilises near zero (–0.4 mL/kg/min and –0.2 mL/kg/min per decade in 2000s and 2010s respectively). This trend was also the case across different sex and age groups, however larger absolute declines were observed for boys, and at the national level this slowing or stabilisation was also evident for a number of countries. If we then juxtapose the CRF of children and adolescents with that of fatness (across a similar time period) we see an apparent decline and increase respectively followed by an evident stabilisation or plateau.
One of the most interesting and important findings of this study however, is the observed negative association between temporal trends in the Gini index (income inequality) and CRF. Meaning that those countries seen to be closing the gap between the ‘haves and have nots’ had more favourable CRF trends (i.e., slowing decline, stabilisation, increase in CRF). It is imperative therefore that we are actively working towards closing the gap with regards to income inequality while targeting at risk groups when implementing programs to improve CRF.
Despite these findings for high- and upper middle-income countries we cannot be sure if the same trends occur for low- and middle-income countries given the lack of data for these populations. It is vital that we advocate for the harmonised and consistent international monitoring of CRF to not only understand what is happening in low- and middle-income countries with regards to CRF trends but to ensure that across all countries CRF is a national priority with regards to surveillance and then intervention where needed.
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