“Jack Johnson” could very well be considered Miles’ “heaviest” music, in the classic rock sense: driven by a straight-ahead, 4/4 beat drums (provided by a 24-year old Billy Cobham), with a popping, electric bass boogie line (19-year old Michael Henderson, fresh from Stevie Wonder’s road band), and a brash, explosive electric guitar sound (a 28-year old John McLaughlin taking center stage next to Miles)—as well as Herbie Hancock on a Fender Rhodes and Steve Grossman on soprano saxophone. Miles himself, on the lengthy workout Right Off—the first of the album’s only two tracks—blows what may be the most truculent, trash-talking solo of his career. Miles created the music for “Jack Johnson“ in two sessions in early 1970, one in February and the second on April 7th of that year. It was the soundtrack to a documentary on the legendary boxer. A year later, the album was released and the film was nominated for an Oscar.

(Information excerpted from milesdavis.com)

Here is a link to Right Off, Part 1:

"RIGHT OFF, PART 1"