Here's an interesting puzzle.
Robb's new orthotic "boots" seem to allow him to walk twice as fast as he normally can. But when he is wearing them, he can only go half as far.
Why is this?
Robb speculates that the reason for this may be that the devices stimulate his feet so much that they cause a lot more neural spasticity. We don't know if this is the case, but it sounds plausible.