Athlean-X (Jeff Cavaliere)

Jeff Cavaliere is the most credentialed fitness YouTuber on the platform — physical therapist, former NY Mets strength coach, and 14M+ subscriber channel that has been correcting bad gym advice since 2006. His "science-based" approach was genuinely revolutionary in a landscape dominated by steroid-adjacent influencers giving dangerous advice. The "stop doing this exercise" series identified movement flaws in popular exercises that have prevented thousands of injuries. If you only watch one fitness channel, this is it.