"A person who doesn't get enough physical activity will quickly put on weight, often cannot concentrate and frequently feels flabby," said Axel Bauer, an expert in physical fitness from Goettingen, Germany.
Too much inactivity is bad for the body, Bauer said, adding that doing an extreme amount of physical activity every day is not what he's talking about. Bauer, associate director of sports in secondary education at the University of Goettingen, said the important thing is to get some physical activity.
"You can walk or ride a bike to school, and take the stairs instead of the elevator," Bauer said. Or, go dancing instead of sitting around at a friend's house watching a video.
Peter Lautenbach of the German Sports Association has a similar outlook. "We are born as active mammals - we need movement to survive," Lautenbach said. Otherwise, the vertebrae will become ever more rigid, joints will get rusty and the muscles will tighten up. It's good to get regular physical activity to prevent these types of things developing in the body.
"It is, however, very important that the activity is fun to do and that it does not become an annoying obligation," said Bauer. It helps to find a sport that can be done with friends. Football, basketball, jogging, in-line skating and table tennis are good examples.
Also, consider a sport in which everyone is at the same level so that the beginners are not left behind by a few who are exceptionally good. A few examples of sports suitable are rock climbing and canoeing. Experts also warn that new virtual games played with a console do not replace real sport. To play the game the participants has to move if they were playing tennis, for example. But only individual body parts are exercised for a few minutes, which is not comparable to actually doing sports.
"At least one hour per day in an activity that brings on a sweat, increases breathing and raises the heart rate to 120 beats per minute would be optimal," said Hans-Joachim Siebert, chairman of the children and youth sport section of the German association for sports medicine and prevention.
Some types of sports, however, come with a warning: "Activities that require repetitive stress on joints such as distance running and weight lifting can be dangerous in youths whose bones have not yet finished growing," said Siebert. That's why one shouldn't start pursuing such sports before the age of 14.
Sports not only does the body good, it has other advantages. It provides opportunities to make friends, for example, while also offering a distraction from aggravations at school, work or home and a chance to let off steam, said Lautenbach.
"Apart from that, over time you can improve and regularly celebrate incremental successes, which does the ego good," he added. Siebert said in addition studies have shown that students who regularly do sports perform better in the classroom.