human machine efficiency

Was on a bus to work today and was struck by these thoughts.
I saw a construction area, where a few people were working, a mixer was mixing cement, sand and stone another big machine was holding a building chasis and bulldozer digging and clearing earth. I started comparing that to my experience in India, how the same scene would have a lot more people, people holding the chasis, people mixing the cement, people digging, somebody screaming orders etc and that set me thinking.

Is there is a lot more energy going into the same construction with the machines versus one with humans. Account for the machine burning petrol, the energy that went into building that machine (ofcourse divided by the buildings it will build, its repair etc), electric power consumed in the factory, factory for that factory etc, compare that to the energy that went into the man doing the same job, how much he eats and drinks, energy to create what he eats etc. Is it more or less, who is more efficient in the end, it will be an interesting calculation. My hypothesis is that for a machine to do the same job a man was doing it consumes more energy than what the man would, biological bodies are far more efficient at using energy than mechanical bodies. Ofcourse machines do it quicker, we might want to bring time into the equation.

This brings up lots of ideas, machines might be faster, but are less efficient. So is it better to use more people to do something or should we come up with machines that work like us to make them more efficient.