Dimitrios Tselios cheerfully swivelled his hips on a stainless steel machine that reminded him of doing the twist 40 years earlier. At the same time, Ulrike Bernal was playing with two large red plastic plates, spinning them with intense concentration.
The sign outside the first playground for pensioners in Germany says that entry is allowed only under adult supervision but that is not much of a problem for Mr Tselios, 74, or Ms Bernal, 69. They, and the other robust pensioners working out in the playground, are part of a remarkable social experiment aimed at making elderly people more physically and mentally agile.
Germany has 16 million people over the age of 65. Pensioners are taking over power while children are rapidly becoming extinct, Der Spiegel lamented. Now cities are trying to bring the principle of play back into the lives of the elderly. Gerold Kolb, the former head of the German Society for Gerontology and Geriatrics and a supporter of the scheme, said: The combination of mental and physical activity can delay the onset of senile dementia.
I come every day for about half an hour, Mr Tselios said. I like the leg-swing best. Mr Tselios, who trained as a car mechanic after moving to Germany in 1963, has arthritis and finds that the swing has started to help him after only a fortnight. The playground was opened in the Prussia Park in Berlin this month and the eight pieces of apparatus cost 20,000 (£13,500) a fraction of the cost of building a childrens playground. Finnish researchers at the University of Lappland experimented with what they called three-generational play and found that older people recorded significant improvement in balance and coordination. Grandparents and children are encouraged to play together.
Children with an accompanying adult are supposedly welcome too in Germanys new pensioner play areas. The elderly, however, disapprove of the youngsters, citing damage to equipment, and are fearful of drug dealers moving in.
Childrens playgrounds in Germany, as in Britain, used to be a place where teenagers hung out: listening to music, flirting, sneering at the little kids and smoking. To prevent this happening in pensioners playgrounds, the benches have been removed and smoking is forbidden. A height-measuring rod stands in the centre of the Berlin playground. Any child shorter than 1.5 metres (5ft) is marched off the terrain. And all the machines have been made graffiti-proof.
The scheme has been brought to Germany by Renate Zeumer, of the Playfit company, who was impressed by the way that China had placed keep-fit equipment in public places. One playground is being set up in Nuremberg and others are being planned across the country. Most will be privately sponsored. The same ground rules apply: no swings, no slides, no bouncy castles.
Germany is the most heavily insured country in the world and no local council wants to risk a playful pensioner having to be stretchered off for an emergency hip replacement.