London, May 20 (IANS): Strict lockdowns can reduce the spread of Covid-19, but might be responsible for delaying normal cardiorespiratory development in children, according to a research.

The study, led by a team of researchers from Anglia Ruskin University (ARU) in the UK and University of Zaragoza in Spain, showed that boys and girls aged 12-14 showed lower levels of cardiorespiratory fitness than would be expected with normal VO2 max rate development.

VO2 max is a well-known cardiorespiratory fitness indicator and levels increase during adolescence, in line with physical growth and development.

Healthy Fitness Zone (HFZ) levels -- a standard measure of health based on age and sex -- also fell by 3.4 per cent over the 12-month period.

"In normal conditions, VO2 max levels tend to increase in adolescents up to a certain age. In our study, each age and sex subgroup showed lower levels in relation to normal VO2 max rate development and specific subgroups, such as boys aged 12 and girls aged 14, displayed reductions in their actual VO2 max levels, which could underscore a higher vulnerability in these groups," said Lee Smith, Reader in Physical Activity and Public Health at ARU.

The research, published in the European Journal of Pediatrics, involved a group of 89 children from a school in north-eastern Spain. The country introduced a strict six-week lockdown in spring 2020, during which under-15s were unable to leave their homes except for medical reasons.

The children, aged 12-14, took part in fitness tests to measure their maximal oxygen uptake (VO2 max) in November 2019, before the start of the Covid-19 pandemic, and repeated the fitness tests in November 2020.

The research VO2 max is a well-known cardiorespiratory fitness indicator and levels increase during adolescence, in line with physical growth and development.