Lefevre picks out the track “Cotton Crop Blues” by James Cotton as a good example of this. Along with the heavier sound, they also began writing lyrics on more morbid subject matters, which is also a trait of heavy metal.
Lefevre then traces the distorted sound of the Memphis blues musicians to the surf rock music of early 1960s America. One aspect this movement added to the heavy metal arsenal, was the use of fast-picked guitars. Then, after these foundations were laid, it was the later 1960s rock groups, many from the UK, that then started really building the demented, accursed path towards metal. As the video notes, many of these groups were inspired by the “grit of American blues.”
So, bands like The Who, with their fast tempos and heavy distortion in songs like “My Generation” and “I Can See For Miles”, the latter of which in turn inspired The Beatles to, legend has it, write “Helter Skelter”. And Eric Clapton’s band Cream and their songs were also a big influence.