Sports scientists and trainers used to regard muscle stretching as an all-round performance booster, helping to prevent injury and sore muscles, but scientific studies have failed to back up either of these alleged benefits, German experts say.
"There are forms of sport where stretching can even be counter-productive," says Ingo Froboese, a professor working in the area at the German Sport University in Cologne.
He points to football or other sports where explosive power is needed. Froboese also believes the muscles are weakened through stretching where maximum effort is required, as with weight-lifting.
Warming up beforehand is much more important, whether going out jogging, playing football or tennis or weight training.
This is usually done by going through the movements typical of the activity slowly and at lower intensity. "So when you want to go jogging, simply run more slowly for the first five minutes. That is sufficient protection against injury," Froboese says.
Juergen Freiwald, a movement expert from the University of Wuppertal, takes a more relaxed attitude. People playing sport for leisure's sake who feel better after stretching should continue with the activity.
"Stretching before taking exercise means that I lose 2 to 5 percent of my maximum performance, and this range is irrelevant to a person playing sport as a leisure activity," Freiwald says.
And he recommends stretching for older people and those suffering from stress. "Stretching can make you more mobile and help retain mobility," he says.
The sports scientists prefer flexible, dynamic stretching for exercise as part of warming up. But after a hard day at work, static stretching is useful, Freiwald says.
The head controls the muscles and the muscles the head, as for example with relaxation exercises like yoga.
When it comes to weight training, Freiwald recommends going through the movements without weights or with light weights.
"The cartilages, muscles sinews and the sinew-muscle transitions cause most of the problems, and this eases them up and prepares them," he says.
In the case of sports with high mobility, such as gymnastics, hurdling and aerobics, the sports scientists see stretching as a necessary part of the warm-up routine. This also applies to the martial arts and to ballet.
But the idea that stretching prevents aching muscles after exercise has little backing.
"There is no researched evidence showing that stretching has a preventive effect on the severity or duration of sore muscles," according to Hans-Joachim Appell Coriolano, anatomy professor at the Sport University.
Nevertheless stretching exercises remain relevant. "Stretching can support muscle relaxation after sport, and stretching can help while taking exercise if there are indications of muscle cramp, Appell says.
In this case, stretching has only a short-term effect.
Over the longer term stretching improves joint mobility.
It can also help to alleviate muscular imbalance by stretching shortened muscles and reducing tension. And it helps those suffering from stress to ease up and relax.