Walking on your heels challenges the body in many ways. Having your weight on the heels will throw your body back and the pelvis will protrude backwards. It takes work to try to lift your pelvis up and tilt it so that your pelvis is under your shoulders and not sticking out behind you. The work of the shins, particluarly in the front part is tremendous. We tend to be weaker in this area due to people's tighness in the back of the shins (calves, soleus and the posterior tibialis and toe flexors). You still want to try to swing those arms making sure you have the spiral of the spine moving. Walking barefoot is preferable for this exercise. If your heels are sensitive, walk on your heels on the carpet rather than a wood floor.