Some of the most popular subgenres of rock workout music include:

✦ Hard rock: This is a heavy and aggressive subgenre that is characterized by distorted guitars, pounding drums, and screaming vocals. Some popular hard rock workout songs include "Thunderstruck" by AC/DC, "Crazy Train" by Ozzy Osbourne, and "You Shook Me All Night Long" by AC/DC.

✦ Classic rock: This subgenre is more melodic and less aggressive than hard rock, but it still has plenty of energy. Some popular classic rock workout songs include "Eye of the Tiger" by Survivor, "Livin' on a Prayer" by Bon Jovi, and "Born to Run" by Bruce Springsteen.

✦ Alternative rock: This subgenre is more diverse than the others, but it generally consists of songs that are more experimental and less mainstream than hard rock or classic rock. Some popular alternative rock workout songs include "Smells Like Teen Spirit" by Nirvana, "Basket Case" by Green Day, and "Song 2" by Blur.

In addition to the subgenres listed above, there are many other types of rock music that can be used for workouts. Ultimately, the best rock workout music is the music that you enjoy the most and that gets you pumped up to exercise.