Health, sex, family, school, even their mobile phones ... everything you ever wanted to know about Scottish teens but were afraid to ask

A similar picture also emerged when it comes to trends among teenage girls. Ten countries showed a significant increase in activity levels but eight countries - including Scotland - showing a significant decrease.

The study has been published in this month's European Journal of Public Health, as one of a series of articles based on data from the Health Behaviour in School-aged Children (HBSC) study, which is collected every four years. The new analysis, spanning the years 2002-2010, compares adolescent behaviour in different countries over a decade, in issues ranging from diet and relationships to exam pressure and bullying.

For the exercise analysis, researchers looked at trends in moderate-to-vigorous activity levels.

In Scotland, the percentage of boys aged 11 to15-years-old achieving one hour daily dropped from 25.2% to 18.3%, while for girls the figure dropped from 13.6% to just 11% - ranking Scotland 26th out of 32 countries for both sexes.

The country with the highest percentage of boys meeting the target was Ireland - at 34.3% - while in Finland the figure jumped from 17.8% to 29.7%.

Greenland achieved the highest percentage for girls at 22%, while Latvia managed to increase levels from 10.8% to 16%.

Study co-author Dr Jo Inchley, assistant director of the child and adolescent health research unit at St Andrew's University school of medicine, said: "Being able to compare Scotland with other international countries allows us to see how are young people in Scotland are really doing and whether we should be concerned - or is this symptomatic of a wider trend among adolescents at European and international level?

"There are no clear trends across the countries taking part in the study - some are increasing (physical activity levels), some are decreasing, some are staying the same."

Speaking of the decrease among Scottish adolescents, Inchley said: "Obviously that is a disappointing result given there has been considerable investment in physical activity to try and get kids more active. Obviously there is more work to be done in this area."

Inchley said that one difficulty was that with technological advances and the development of a more sedentary environment, physical activity had become a "positive choice" that people opt into.

She added: "While there are countries doing better than others, there are not any countries that are doing well, as overall the proportion of kids who meet the guidelines is really low.

"However we are seeing some countries that have seen an increase over time - so that would be the next step, to really understand what is it that is going on in those countries which is really facilitating that change - can we learn lessons from them?"

She acknowledged the study had finished before events such as the last year's Commonwealth Games in Glasgow and said the publication of the next HBSC data - due this autumn - could provide an insight into whether that has had an impact.

A spokeswoman for the Scottish Government said it had invested £11.6million between 2012 and 2016 in providing physical education for primary and secondary school pupils.

She added: "We are investing £500,000 annually to increase the number of teenage girls taking part in PE.

"Since 2007 sportscotland has invested over £80 million in the Active Schools Programme and support for Active Schools was reinforced on July 3 2014 when sportscotland announced that it will invest up to £50 million over 2015-19 across all 32 of Scotland's Local Authorities."

Here we look at some of the other research findings published in the European Journal of Public Health which examine the trends of the HBSC study:

Diet

Diets high in fruit and vegetables can have a positive impact on long-term health, including lowering the risk of diseases such as stroke, cancer and heart attacks. But studies to date have indicated most teenagers in Europe and North America fail to meet the World Health Organisation recommendations of at least 400g per day.

An analysis of the HBSC data found there has been an increase in daily fruit and vegetable consumption among 11, 13 and 15 year olds in most countries. Denmark and French Belgium recorded the highest number of teenagers consuming fruit daily - at 49% - while Greenland recorded the lowest at 15%. Daily vegetable consumption ranged from 20% in Estonia to 55% in Flemish Belgium.

The most pronounced increases in fruit consumption were found in Denmark, England, Norway, Ukraine, USA and Wales, while significant decreases were noted in Germany, Greece, Poland and Portugal. Significant increases in vegetable consumption were noted in Spain, Denmark, Hungary, England, Wales, Greece and Austria, while Germany, Lithuania, Latvia, Poland and Russia recorded significant decreases.

For Scotland, the figure for both daily fruit and vegetable consumption was around 36% in 2010, a rise from just over 30% in 2002.

Communication

With a surge in use of smartphones and social media in recent years, it is unsurprising that researchers found an overall rise in teenagers talking on the phone, sending text messages or contacting friends on the internet. A study of 30 European and North American countries found overall 29% of 11-year-olds used these forms of electronic media communication (EMC) five days or more per week in 2002, but by 2010 this had risen to 41.8%. For 13-year-olds the figure rose from 42.8% to 61.5% and for 15-year-olds it rose from 51.7% to nearly three-quarters - 72.8%.

The use of EMC by Scottish teenagers was above this average. By 2010, nearly half - 46.6% - of 11-year-olds used EMC five times or more per week - up more than 10% on the figure in 2002 and ranking Scotland ninth out of 30 countries. For children aged 13-years-old it rose from 56.8% in 2002 to 70.6% in 2010, ranking Scotland in fourth place. For 15-year-olds nearly eight in ten - 79.1% - were using EMC five or more times a week, compared to 66.2% in 2002, ranking Scotland in fifth place.

Lithuania recorded the highest usage in all three age groups, with around 82% of 15-year-olds using EMC five or more times per week in 2010. The Netherlands recorded the lowest usage for 11-year-olds at 17.1% in 2010 and for 13-year-olds with 49.4%. Germany recorded the lowest usage for 15-year-olds, at 63.6%.

However the researchers also found that - contrary to worries about electronic media increasing isolation among youngsters, it made it easier to communicate with friends, especially those of the opposite sex.

Relationship with mum and dad

The teenage years are more known for sulks and tantrums than cosy chats with mum and dad. But the quality of communication with parents is associated with self-esteem and mental and physical wellbeing.

One of the studies looked at trends in adolescent's communication with their parents from 2002 to 2010, rating how easy girls and boys found it to talk with their mothers and fathers. Overall there has been an increase in the ease with which teenagers of both sexes talk to their fathers, according to data. However, when it comes to speaking to mum only boys seem to be finding it easier, girls are unchanged. The researchers note that these trends may be partly due to changes in attitudes to parenting particularly among fathers.

The Scottish results of the study show it was one of nine countries which recorded a decrease in ease of communication with fathers for both boys and girls - but it was the lowest drop at less than 1%. The highest decreases were found in France, at 20% for girls and just over 15% for boys. Wales recorded the biggest increase at just over 10% for girls and just under 10% for boys.

When it comes to communication with mothers, there was a 5% decrease in Scotland for girls and a small improvement of less than 1% for boys. Again, France recorded the biggest decrease at more than 10% for both sexes while Estonia had the biggest improvements, with an increase of just over 5%.

Bullying

One study assessed how often children reported being bullied at school - and found while it is still common in many countries, overall the trend decreased in many countries across the decade of the research.

In Scotland, the experience of being bullied once or more in recent months dropped for both sexes between from 27.8% to 23.8% for boys and from 30.1% to 23.3% for girls. Twenty-five out of 33 countries had higher bullying rates than Scotland for boys and 22 out of 33 countries for girls. French Belgium recorded the highest rates of bullying for boys - at 59.7%, while the lowest was in Sweden at 12.4%. For girls, the highest figure was 52.8% in Lithuania, while the lowest was in Italy at 8.4%.

However for more frequent bullying - counted as at least two or three times in the past couple of months - there was a small rise for boys in Scotland - from 8.4% to 9.8%. The figure for girls in Scotland dropped from 9.1% to 8.5%. The highest rate for more frequent bullying of boys was in Lithuania, at 28.5%, while the lowest was 3.9% in Sweden. For girls, Lithuania also recorded the highest rates at 23.4% while Italy had the lowest at 2.9%.

The researchers note that bullying and victimisation is still a "fairly common harmful experience for a number of school aged-children".

Exams

Researchers have also scrutinised the issue of pressure in school, relating to academic demand and expectations. The study noted that pressure to succeed can have a positive or a negative impact on learning, health and emotional well-being. Across the countries examined, girls reported higher levels of pressure than boys. But between 1994 and 2010 there was no change in the reported perceptions of school pressure. In 1994, an average of 21% of pupils reported feeling some or a lot of pressure over time - a figure which stood at 22% in 2010.

In Scotland, 34% of pupils reported feeling pressure in 2010 - the lowest rate in the UK, but up from 30% in 1994. Scotland ranked 10th out of 23 countries for the highest levels of pressure. Broken down by age group, 23% of 11-year-olds in Scotland said they felt pressure, but this had increased to 48% by the age of 15.

Finland recorded the highest figure for school pressure at 44% - but this represented a significant decrease from 52% in 1994. North American and Canadian pupils also reported high levels of pressure, at 42% and 48% respectively. The pupils least likely to be feeling pressured were in Greenland, which recorded a figure of 18% and Austria, with 19%.

Happiness

The life satisfaction of adolescents in more than 30 countries between 2002 and 2010 was analysed by researchers. The study found a varied picture - with 12 countries having increased levels of happiness among teenagers, seven countries where the levels went down and 12 countries where the pattern did not change. The happiest teenagers in 2010 were in the Netherlands, which a recorded life satisfaction rate of rate 94% - slightly down from the 2002 figure of 94.2%. Even before the hostilities with Russian separatists, Ukraine recorded the lowest rate at 79.2% in 2010.

For Scotland, the figure was 85.9% in 2002 - and by 2010 this had increased to 87.5%, ranking it as the sixth happiest out of a total of 33 countries.

The researchers found overall life satisfaction had decreased in six relatively affluent countries between 2002 and 2010 - Austria, Canada, Switzerland, Denmark, Finland and Greenland - and two belonging to former Eastern European countries - Hungary and Macedonia.

However increasing life satisfaction was recorded in a group of Eastern European countries including Estonia, Croatia, Lithuania, and Latvia, and in four Western European countries - Spain, Norway, Portugal and Belgium.

The study also found that girls have a tendency to have lower levels of life satisfaction than boys in most countries - with the exception of Latvia, Macedonia and Ukraine - and happiness tends to decrease as the teenagers get older.

Sex

One study looked at trends across 20 countries in relation to the age at which adolescents first had sex and condom use. In 2010, the lowest percentage of 15-year-old boys who said they had ever had sex was in the Netherlands - at 19.1% - and the highest figure was recorded in Ukraine, at 39%. For girls, the lowest figure was 2.7% in Macedonia, while the highest was 38.8% in Wales.

In Scotland, 26.6% of 15-year-old boys said they had had sex in 2010, a drop compared to the figure of 32.7% in 2002 - 11th highest out of 20 countries. For girls of the same age in Scotland, the figure was 35.3% in 2010 compared to 34.6% in 2002 - the second highest figure out of 20 countries, behind Wales. There has been a increase in the proportion of these youngsters first having sex aged 13 or younger. The figures for Scotland show 8.6% of the 15-year-old boys who reported being sexually active first had sex aged 13 or younger in 2010, compared to 7.6% in 2002. However, for girls, the percentage dropped from 10.1% to 7.4% over the same time.

The study found there was an increase in condom use in all regions among girls, and in half of them for boys. In Scotland, 70.5% of 15-year-old girls reported using condoms in 2010, up from 63.4% in 2002. However for boys the figure dropped from 72.8% in 2010, compared to 75.1% in 2002.