There was a wide variation across countries with proportions of young people meeting the PA guidelines ranging from 26% in Belgium (Flemish) to 57% in Ireland for boys and 12% in France to 44% in USA for girls. In all countries and across all age groups, more boys (mean 40%) than girls (mean 27%) met the UKHEA PA guidelines although the gender differences were small in some countries. A strong trend of HPA decreasing with age was noted.21 Data from 16,410 U.S. adolescents from the 2009 Youth Risk check details and Behaviour Surveillance Survey (YRBSS) indicated that 37% of 15–18-year-olds experienced PA that increased their HR and made them breathe

hard some of the time for a total of at least 60 min per day, on at least 5 days per week. More boys than girls (46% vs. 28%)

met the PA guideline. 34 A survey of 32,005 13–18-year-olds from Hong Kong, China reported 64% of Chinese boys and 40% of Chinese girls to achieve 60 min of moderate intensity PA after school on 5 days per week. Similar to studies of western youth a declining trend of HPA with age was observed.35 A study of 2101 6–18-year-old Russians used the ICC PA guidelines and reported that although nearly 70% of Russian youth met the PFT�� nmr guideline for daily PA fewer than 45% met the guideline advocating sustained periods of MVPA. A marked decrease with age in the percentage of young people who experienced sustained periods of MVPA was noted with none of 17–18-year-olds meeting this PA guideline.36 Although the use of different methodology means that comparisons must be carried out cautiously, however a recent WHO sponsored survey of 72,000 youth, aged 13–15 years, from 34 developing countries suggests that self-reported levels of HPA from developing countries are lower than those from Europe, China and North America. Only 24% of boys and 15% of girls were reported to experience 60 min of daily MVPA.23 Studies using pedometers provide limited insights into the percentage of young people meeting PA guidelines but

they are consistent in reporting boys to be more active than girls at all ages from 7 to 18 years with HPA declining in both genders with age.3 One study of Canadian youth used a cut-off point of 15,000 steps per day as a guideline and reported 6%–17% of girls and 14%–33% of boys to meet this target.37 The percentage of young people reported to be physically active in studies using accelerometers varies from 0 to 100% depending on the activity cpm defining the required intensity of PA.7 For example, 2185 9- and 15-year-olds were recruited from four European countries and monitored for 3 or 4 days including, where possible, both weekend days. Using total activity counts boys were more active than girls at both ages and the 9-year-olds were more active than the 15-year-olds. The authors estimated that at 9 years >97% of children and at 15 years 82% of boys and 62% of girls experienced 60 min of moderate PA per day.