How does the human machine compare with a gasoline engine with regard to mechanical efficiency?
Yes, we can compare the humans with gasoline machines because the muscles take up energy to do work. If we want to compare their efficiencies, we have to compare the energy consumed and work done. For example, a 77 kg person raiding bicycle at a speed of 15 miles per hour burns about 34 calories per each mile.
In case of gasoline, 4 liters (= one gallon) contains 31, 000 calories. If a person drinks gasoline, can ride about 912 miles per each gallon. A car consumes about a gallon of gasoline per 30 miles. But, we should consider the weight and speed of the car, they are different from bicycle.