Slowest Possible Bicycle Speed: A Detailed Look
There is no definitive answer to this, as it depends on a number of factors, including the terrain, the rider's fitness level, and the type of bike. Generally speaking, however, the slowest a human can ride a bike is around 1 mile per hour. This is roughly the speed of a very slow walk, and it would be difficult to sustain this speed for long periods of time without becoming fatigued.
Bicycle Speed: How Far Can You Travel in an Hour?
Cycling with a Broken Ankle: Risks and Recovery