What inherent limitation defined the direct-drive pedals on the 'boneshaker' or 'penny-farthing'?

The speed of the bicycle was entirely dependent on how fast the rider could pedal (one pedal turn equaled one wheel turn).

Direct-drive systems, characteristic of early designs like the boneshaker and the high-wheeler, fundamentally linked the rotation of the pedals directly to the rotation of the driven wheel. This 1:1 relationship meant that if the rider pedaled slowly, the bicycle moved slowly, and if the rider tried to pedal very fast to increase speed, they would quickly reach a physiological limit where their legs could no longer move quickly enough to generate efficient power or maintain control. This dependency made hill climbing extremely difficult, often necessitating the rider to stand and exert immense torque or simply get off the machine.