The study, published in the journal The Lancet Child & Adolescent Health, based on data reported by 1.6 million 11 to 17-year-old students - found that across all 146 countries studied between 2001-2016, girls were less active than boys in all but four (Tonga, Samoa, Afghanistan and Zambia).
According to the WHO, levels of insufficient physical activity in adolescents continue to be extremely high, compromising their current and future health.
"Urgent policy action to increase physical activity is needed now, particularly to promote and retain girls' participation in physical activity," said study author Dr Regina Guthold, WHO.
Most countries in the study (73 per cent, 107 of 146) saw this gender gap widen between 2001-2016.
The study also found that Bangladesh and India had the lowest rates of physical inactivity for boys and girls.
For the findings, the researchers estimated how many 11 to 17-year-olds do not meet this recommendation by analysing data collected through school-based surveys on physical activity levels.
The assessment included all types of physical activity, such as time spent in active play, recreation and sports, active domestic chores, walking and cycling or other types of active transportation, physical education and planned exercise.
Physical activity trends show slight improvement for boys, none for girls
The study found that the greatest decreases in boys being insufficiently active were Bangladesh from 73 per cent to 63 per cent, Singapore (78 per cent to 70 per cent), Thailand (78 per cent to 70 per cent), Benin (79 per cent to 71 per cent), Ireland (71 per cent to 64 per cent), and the US (71 per cent to 64 per cent).
However, among girls, changes were small, ranging from a two percentage-point decrease in Singapore (85 per cent to 83 per cent) to a one percentage-point increase in Afghanistan (87 per cent to 88 per cent).
Bangladesh was the country with the lowest prevalence of insufficient physical activity among boys, girls, and both genders combined (63 per cent, 69 per cent and 66 per cent, respectively).
Some of the lowest levels of insufficient activity in boys were found in Bangladesh, India and the US.
The authors noted that the lower levels of insufficient physical activity in Bangladesh and India (where 63 per cent and 72 per cent of boys were insufficiently active in 2016, respectively) may be explained by the strong focus on national sports like cricket.
For girls, the lowest levels of insufficient activity were seen in Bangladesh and India, and are potentially explained by societal factors, such as increased domestic chores in the home for girls.
The authors noted that if these trends continue, the global target of a 15 per cent relative reduction in insufficient physical activity - which would lead to a global prevalence of less than 70 per cent by 2030 - will not be achieved.
This target was agreed to by all countries at the World Health Assembly in 2018.
( With inputs from IANS )