Walking is so easy, as long as you are able to do it. Emulating human gait, by a robot, is not easy at all, and a lot of work has and is taking place to have a robot walking as seamlessly as a human. At the same time work is progressing to provide people who have been amputated a prosthetic that can work as well as a natural leg.
Progress have been made in this area as well, as an example we now have prosthetic legs that can work to go up on a staircase, something that just three years ago was impossibile.
Now at the University of Texas in Dallas a team of researchers have managed to create a prosthetic leg that can work seamlessly with the natural leg (the one remaining for an amputee).
They started with a careful study of the human gate noticing that modelling can be simplified by looking at how the pressure point of the sole of the foot moves from the heel to the toes as one walks. There are plenty of things going on as you walk, tendons stretching, muscles pulling, joints transferring pressure and directions but an accurate modelling of the foot pressure point movement seemed in the computer simulation to be quite effective.
Once this was done they tested the "robotised" prosthetic leg on three people who lost the lower part of their leg and found that, indeed, the results were good. 15 minutes were sufficient to adapt the prosthetic leg to the specific person and once that was done the person was able to walk normally. This is quite different from current prosthetic legs that require a fine, and lengthy, tuning of knobs before "fitting" on a person.
They also had the person walking on a treadmill reading a speed of 1m per second, that is not far from the average walking speed (1.3 m per s). There was no need to feed information of changing treadmill speed, the prosthetic leg reacted smoothly as the biological leg by sensing the changing movement speed of the pressure point on the artificial foot.
Most importantly, the feedback from the persons that tried them were very positive...