Besides gasoline, what external power sources did inventors experiment with for early motorized assistance?

Steam and electricity

The historical journey toward assisted locomotion involved simultaneous experimentation with several external power sources before gasoline engines became dominant. Inventors explored harnessing the power of steam, which offered significant motive force but often resulted in bulky, heavy machinery unsuitable for light bicycle frames. Electricity was also an early contender, as seen in subsequent electric bicycle patents. This branching evolution shows that the development was not strictly linear toward internal combustion; rather, inventors pursued any available compact power source that could potentially reduce the physical effort associated with cycling, even if the technology eventually proved impractical or too cumbersome for widespread adoption.