Torque sensors and power controls were developed in the late 1990s. For example, Takada Yutky of Japan filed a patent in 1997 for such a device. In 1992 Vector Services Limited offered and sold an e-bike dubbed Zike. The bicycle included NiCd batteries that were built into a frame member and included an 850 g permanent-magnet motor. Despite the Zike, in 1992 hardly any commercial e-bikes were available.
If you have dynamo-powered bicycle lights, you already own an electric-powered bicycle! Consider: as you pump your legs up and down on the pedals, you make the wheels rotate. A small dynamo (generator) mounted on the rear wheel produces a tiny current of electricity that keeps your back safety lamp lit in the dark. Now suppose you could run this process backward. What if you removed the lamp and replaced it with a large battery. The battery would kick out a steady electric current, driving the dynamo in reverse so that it spun around like an electric motor. As the dynamo/motor turned, it would rotate the tire and make the bike go along without any help from your pedaling. Hey presto: an electric bike! It may sound a bit far-fetched, but this is more or less exactly how electric bikes work.
There are individuals who claim to have lost considerable amounts of weight by using an electric bike. A recent prospective cohort study however found that people using e-bikes have a higher BMI. By making the biking terrain less of an issue, people who wouldn't otherwise consider biking can use the electric assistance when needed and otherwise pedal as they are able. This means people of lower fitness levels or who haven't cycled in many years can start enjoying the many health benefits E-bikes have to offer.