Since nobody has chimed in with some physics yet, I guess I'll take a crack. You use different muscles to apply backpressure during different parts of the stroke. Generally, the muscles you use to decelerate during one part of the stroke will be similar to/the same as the ones you use to _accelerate_ a half-stroke later. For example, (I believe) you use mainly your quadriceps to apply backpressure during the bottom of the stroke, and conversely, you use mainly your quadriceps to apply forward pressure at the top of the stroke.

Consequently, to slow down effectively with backpressure, you have to be able to activate large leg muscles/muscle groups and deactivate them before you reach the opposite side of the stroke (half-a-pedal-revolution later). The maximum rate at which you can activate and relax your muscles will undoubtedly vary with practice, muscle constitution, and other variables. When I pass this limit, I find that I can't synchronize my legs enough to actively slow down -- by the time I tell my quadriceps "Go!" at or slightly before the bottom of the stroke, I'm at the top of the stroke (or later), and I either accelerate or don't do anything useful at all.

I would guess that given how much forward walking practice most people have had, the maximum acceleration rate (RPMs) that a person can coordinate will be much higher than the maximum deceleration rate (again, RPMs); I've certainly found that this is the case for myself.

Furthermore, skipping, skidding, and other methods of slowing down at high RPMs are generally all methods of applying opposing force while having your legs rotate slowly enough to coordinate muscle activations.