By what definition? Horsepower? Torque? Both??? I'm sure we can all agree that the "Muscle Era" was generally 1968-1972, though we can sometimes paint that with a broader brush and say 1964-1974
Be careful with the word "all".
The first known use of the word "muscle" to describe a car was auto writer Tom McCahill who, after the road test of a '55 Chrysler 300, said "Detroit has finally built a car with true Muscle."
