Brian Mackenzie
Fitness Instructor
American fitness instructor and entrepreneur who is best recognized for having co-founded the Extreme Performance Training program. He is also known for having finished the Angeles Crest 100-mile endurance run.
He began studying altitude and hypoxic training in 2006.
He published a book titled Power Speed Endurance.
He married Olympic gold medalist Erin Cafaro MacKenzie.
In March 2017 he posted a photo with fellow fitness instructor Emily Bridgers to his iamunscared Instagram account.