Who does work while walking? 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.
 A: 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.
A: This subject has been studied experimentally a lot. For example, this study using markers placed on the body of walkers and an array of camera concluded that the motion of the centre of mass (COM) is as follow
 
Every time the COM goes up, an upward force has to produce a positive work $W$ to explain the increase of gravitational potential energy. The range of the mass $m$ of the subjects in this experiment was from 56.8 to 83.6 kg. Since the range of upward motion $h$ is 2.74 cm to 4.89 cm according to the figure above, the work $W=mgh$ is in the range 15 to 40 J.
What does this work? The quadriceps, the gluteal muscles and the calf muscles mostly. The torque of the weight with respect to the knee is opposed by the torque of the force exerted by the quadriceps on the top of the tibia. This is that force caused by the shortening of the quadriceps that produces work. There is some work done by the calf muscles and the gluteal muscles: similar story but with the articulation of the ankle and the articulation of the hip, respectively. I think the quadriceps and then the gluteal muscles do most of the work.
A: I can't click the comment button so I will post here: there is still friction but unlike tires it doesn't oppose but it holds your feet without which you might slip ay every step.
The  work is done by your muscles, but if you go deeper it is your muscular system controlled by your nervous system being supported by your  skelet system and maintained by your circulatory system aided by your respiratory system and a lot more
@CuriousOne: of course they will do because of the lactation of your muscles but theres a way to lessen that ache if you intake something like whay protein i forgot the name of the specific content of it, that coagulates with the lactic acid, but it turns lactic acid into something more useful to your muscle,
A: Your muscles do some work when you start to get you up to walking speed. According to physics there is no work being done once you get up to a constant speed. At a constant speed there is no acceleration, no force, and no work. Unfortunately, just because you aren't doing any work doesn't mean your muscles aren't consuming any energy, muscles are inefficient like that.
When you are climbing up a hill or a ladder you are doing work in a physical sense, since you are fighting gravity trying to pull you down. Your muscles then have to consume extra energy, some of it ends up doing work to make you go up and some gets wasted in your muscles.
A: Prologue:
There are friction while you walk (try do it over a very slippery surface and tell me the result). Also your legs are designed to move over irregular surfaces and do other amazing things like climb, swin and swing.
By using a bicycle you can move forward over a flat surface in a more efficient way but most other things ill be a more difficult to do.
That's because the walking mechanism is just a lot more complex what simple moving muscles. In fact while some are contracting others are relaxing in a syncronized way to move your squeleton and that is supporting all the other systems as whole. Also there are all the other muscles like the heart and diafragma bombing blood and air for the entire setup.
Answer:
The work is done by your body as a whole against gravity and friction
A: 
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.

Work is the transfer of energy by a macroscopic force. There is no energy being transferred between your feet and the ground, so you don't do any work on the ground and the ground doesn't do any work on you. You can also see this from the equation $W=Fd$. At the point of contact between your foot and the ground, there is no motion, so $d=0$ and $W=0$.
The question seems to be predicated on the assumption that any energy transformation must involve mechanical work. That's simply not true. For example, there is no mechanical work involved in heat conduction.
The energy transformation that occurs when you're walking is that the electrical potential energy in your food (or ATP or glycogen) is being transformed into heat, while your body's KE stays approximately condstant.
A: You push the earth back and the earth pushes you forward by static frictional force.
Net work done by static friction is always 0 on the system consisting of your feet and the ground.
The kinetic energy that you gain while walking or running comes from the internal energy of your muscles.
A: Let's try to look at it from two different perspectives:


*

*Internal work:


Like work requires to stretch a spring, you do work or spend energy while stretching and contracting the leg muscles and also (angle) bending your legs.


*External work:


2a. When you move a crate on a horizontal surface, you do work if you have to work against the frictional force. If the friction is F and the crate (or your body) is displaced by d, then work done W by you is W=Fd  (irrespective of the body mass or weight; which factors in friction). F will be larger for heavier bodies.
2b. When you walk, the center of gravity (CG) of your body moves slightly up (while legs crossing each other) and down (legs apart). Here, while taking your CG up you do work against gravity. Now think of you are repeating a process of raising a stone to a certain height and dropping it down. Each time you raise you do work; each time you drop you are not doing any work! (I may need expand this 2b further).
A: When you are walking you are doing work against gravity and friction.
Consider this - when you walk on a flat surface, you shift your body weight on to say right leg. Lift the left leg and move it by a step. For the next step, you shift the weight on the left leg, lift the right leg and move forward. Thus you move.
What is the work done?
The leg consists of foot and leg. This makes up approximately 6% of the total body weight. You have 2 legs. So one leg + foot weighs 3% of the total body weight.
Thus if a person weighs 50 kg, than the weight he shifts for each step will be 1.5 kg = 15 N
Thus when a person walks a straight distance of 1 km, he will be working approximately 15,000 J
Do not try to convert into calories. As the medical data of 'calories burnt' represent the heat generated by the body. It has nothing to do with the physical work done
I hope, I have provided an explanation...
A: I think work done by human is 0 because there is no displacement of earth by man , so- d=0and w(work done by man)=0 
