Kinesin-1 is a protein that plays a crucial role in intracellular transport. It is a molecular motor with a directional bias, hydrolysing one ATP molecule per forward step along the microtubule (its molecular track). To improve our understanding of how kinesin works, I have addressed how the mechanochemistry (force-dependent reaction pathways) of backward steps differs from that of forward steps, and how cargo size affects the motor. My research has involved single-molecule optical-trapping experiments and mechanochemical modelling.