Bremen- For most people, cycling is a means of improving their health and boosting fitness which only makes it all the more confusing why people are suddenly flocking to electric bicycles.

Pedelecs and e-bikes take some of the sweat out of biking, letting an engine take over part of the work.

Numbers attest to their popularity. "The number of electric bicycles sold doubled in 2007 from 20,000 to 40,000," said Siegfried Neuberg of the ZIV Bicycle Industry Association in Bad Soden, Germany. "The trend will continue in 2008."

Oliver Hensche, head of sales at Giant Bikes in Erkrath is similarly optimistic: "We expect this to continue for the next three years."

That would mean 100,000 electric bikes sold in Germany in 2010. Figures from the Netherlands show that Germany is no anomaly. "The sales figures are up 260 percent there."

But not all electric bicycles are alike. ZIV notes differences between pedelecs and e-bikes which affect their relative popularity.

The motor on a pedelec is designed to give the cyclist a boost. A pedelec's motor is limited to a 250 watt capacity and it cannot power the bike to go faster than 25 kilometres per hour. Pedelecs are still considered bicycles, meaning neither insurance nor a driver's license is required.

It's a different story with e-bikes, which are considered light mopeds under German law. Like motorcycles, power output is set with a controller in the bike's grip. Motors can have a capacity of up to 500 watts and reach speeds of 20 kilometres per hour. An operating permit and insurance are both required before operating an e-bike.

Pedelecs have driven the trend. However, new leaps in technology, particularly battery capacity, have helped. "Modern batteries with lithium technology have crowded out just about every other model of battery," says Christoph Rasch of the General German Bicycle Club (ADFC) in Bremen. "These batteries offer the same capacity, but weigh and cost less."

The batteries also have broader ranges. Some models advertise that one charge can last for 160 kilometres. But Rasch says such claims need to be viewed skeptically.

"The range of a battery depends on a lot of different factors, including: battery capacity, which is measured in amp hours (ah), the steepness of the stretch travelled, the weight of the bicyclist, luggage, the temperature and the chosen assistance mode."

The latter refers to the setting which decides how much power the motor provides.

Pedelecs are not cheap. Neuberger says prices start at around 1,500 euros (2,368 dollars), but can go up to 3,000 euros. (dpa)