Depends on your definition of muscle. Ferrari, Lamborghini, Audi, Mercedes, BMW all make very fast cars. To me Mercedes seems to fit the muscle definition the best with cars like the Mercedes-Benz SLS AMG.
I agree that it depends on the definition. Honestly, I think that cars like the C63/E63 and BMW M5 fit the bill, especially pre - current era where every car must perform well on a racetrack. Big cars with big engines that go very fast and can fit your family. The original muscle cars were just sedans with big V8s in them.