While walking, the work done by friction is zero.
But who does the work, actually? How someone is getting displaced?
This situation also arises when someone climbs without slipping or is climbing a ladder.
Newtonian Mechanics – Who Performs Work While Walking? Exploring the Forces Involved
everyday-lifeforcesfrictionnewtonian-mechanicswork
Best Answer
Even just walking on flat ground is doing some work in the physics sense. Your center of mass will bounce up and down with each step. The up part requires work to be done, and the body has no mechanism to derive energy from joints being moved by external forces, so can't recover the work on the way down. At best the body could be a spring, which happens to a small extent, but human tendons don't make very good springs. So basically we pay for the up motion with work done by muscles, but don't get much back from the down motion.
Then there are also the legs individually moving. Their centers of mass are going up and down too, which is more work that is largely not recovered on the way down.