[mrob]

"Up to" is reasonable because it varies so much. Energy efficiency of cycling depends strongly on aerodynamics. A fully faired recumbent like you see in the human powered vehicle record attempts will do much better than a normal upright bicycle, probably better than 5x walking. Skin-tight clothing vs. normal clothing makes a big difference. Even shaving legs makes a very small but measurable difference. And because drag increases with the square of the air speed, aerodynamics is more important when you're riding fast. This contributes to the wasted energy on hills too, because you descend much faster than you ascend.

For these reasons it doesn't make much sense to talk about exact figures for energy efficiency of cycling without specifying what type of bicycle, what clothing, what weather conditions, what terrain, what braking technique, how much the rider weighs, their riding position, how fast they're riding, etc. The tires and the drivechain make a noticeable difference too.