That book described total energy expenditure for an individual per distance traveled. It does not improves much even after years of training. It is interesting

That book described total energy expenditure for an individual per distance traveled. It does not improves much even after years of training. It is interesting that for running the efficiency does not depend on speed as wind drag does not contribute much below 20 km/h. This is different from walking. Walking at relaxed pace is the most efficient and uses 2 times less energy per distance than running. At about 7 km/h walking becomes less efficient than running.