Teenagers have long been told that being active and taking part in various sports is good for their health. But new research suggests that too much sport for teenagers could negatively affect their well-being just as much as too little sport.

Researchers from Switzerland say their study suggests that 14 hours of physical activity a week is best for promoting good health in teenagers. However, they found that more than 14 hours appears to be detrimental to their health. To reach their findings, the researchers surveyed more than 1,245 teenagers aged between 16 and 20 from Switzerland.

All participants were required to answer questions on height and weight, sports practice, sports injuries and well-being. Their well-being was assessed(评估) using the World Health Organization (WHO) Well-Being Index,and the average well-being score for all participants was 17.

The researchers divided sports participation into low (0—3.5 hours a week), average (3.6— 10.5 hours), high (10.6— 17.5 hours), and very high (more than 17.5 hours).The researchers found that participants in the low and very high activity groups were more than twice as likely to have well-being scores below 13, compared with participants in the average group. The researchers found that the highest well-being scores were gotten by participants who carried cut around 14 hours of physical activity a week, but exercising beyond 14 hours resulted in lower well-being scores.

Commenting on their findings, the researchers say physical activity has been connected with positive emotional well-being, reduced sadness, anxiety and stress disorders, and improved self-respect in teenagers.

The researchers suggest that their study stresses the importance for physicians caring for teenagers to check their level of sports practice and ask them about their well-being. Teenagers probably need a supportive and closer follow-up of their health and well-being. The findings can provide information for guideline groups who produce recommendations on sports practice for teenagers.

Why can’t we stop longing for the good old days?

People in many countries are longing for the good old days. But when exactly were the good old days? Podcaster Jason Feifer devoted an episode of his program to this question. The most popular answer seemed to be the 1950s, so Mr. Feifer asked historians whether Americans in that decade thought it was particularly pleasant. Definitely not. In the 1950s, American sociologists worried that rampant individualism was tearing the family apart. There were serious racial and class tensions, and everyone lived under the nuclear threat.

In fact, many in the 1950s thought that the good old days were to be found a generation earlier, in the 1920s. But in the 1920s, child psychologist John Watson warned that because of increasing divorce races, the American family would soon cease to exist. Many people at the time idealized the Victor inn era, when families are strong and children respected their elders.

Why are human beings always so nostalgia for past eras that seemed difficult and dangerous to those who lived through them? One possibility is that we know we survived past dangers, so they seem smaller now. But we can never be certain we will solve the problems we are facing today. Radio didn’t ruin the younger generation, but maybe the smart phone will.

Another reason is that historical nostalgia is often colored by personal nostalgia. When were the good old days? Was it, by chance, the incredibly short period when you happened to be young? A U.S. Poll found that people born in the 1930s and 1940s thought the 1950s was America’s best decade, while those born in the 1960s and 1970s preferred the 1980s.

This kind of nostalgia has neurological roots. Researchers have found that we encode more memories during adolescence and early adult hood than any other period of our lives, and when we think about the past, this is the period we most often return to. Moreover, as we grow more distant from past events, we tend to remember them more positively.

Obviously, some things readily were better in the past. But our instinctive nostalgia for the good old days can easily deceive us, with dangerous consequences. Longing for the past and fear of the future inhibit the experiments and innovations that drive progress.

Vaccination, steam engines, railroads and electricity all met with strong resistance when they were first introduced. The point isn’t to show how silly previous generations were. The same kinds of anxieties have been expressed in our own time about innovations like the internet, video games and stem-cell research.

And not all fears about the future are unbounded. New technologies do result in accidents, they disturb traditional cultures and habits, and they destroy old jobs while creating new ones. But the only way to learn how to make the best use of new technologies and reduce risks is by trial and error. The future won’t be perfect, but neither were the good old days.

The United States estimates that about one out of every 10 people on the planet today is at least 60 years old. By 2050, it’s projected to be one out of 5. This means that not only will there be more old people, but there will be relatively fewer young people to support them.

Professor Richard Lee of the University of California at Berkeley says this aging of the world has a great effect on economics. “Population aging increases the concentration of population in the older ages and therefore it is expensive,” he said.

Aging populations consume (消耗) more and produce less. With more people living longer, it could gel expensive. But Mr. Lee says with continuing increases in worker productivity and wise planning, it can be manageable.

Societies have different methods for caring for the elderly，but each carries a cost Generally, there are three types of support Seniors can live off the wealth they gained when they were younger. They can rely on their family to take care of them, or they can rely on the movement.

In industrialized nations, governments created publicly-funded (公共资助的) support systems. These worked relatively well until recent years, when aging population growth in places like the United States and Western Europe began to gradually weaken the systems’ finances(资金). These nations now face some tough choices. Mr. Lee says the elderly in some of these countries must either receive less money, retire later or increase taxes to make the system continuable.

Most developing nations haven’t built this type of government-funded support, but have instead relied on families to care for their elderly. These nations also generally have a much younger population, which means their situation is not as urgent as more developed nations. But Mr. Lee says that doesn’t mean they can pat no attention the issue. “Third World countries should give very careful thought to this process, to population aging and how it may affect their economies — now, before population aging even becomes an problem,” he explained.