I think in this case the interpretation would be

axis1 = UP & DOWN,

axis2 = FORWARDS & BACKWARDS,

In practice the walking gait (the path of the foot) should not track a circle,
The idea is to stop people putting feet on a wheel calling it a walker and claiming the extra weight!

So the mechanism should lift the foot, extend it forward, place the foot on the ground, support the weight of the robot, and then power backwards propelling the robot forward, the foot is then at the start position to do it all over again.

In combat few mechanisms have been able to do that well with this form of propulsion but I hope to do something in the next few years if funds permit!