Brian is the author of the New York Times bestseller Unbreakable Runner, as well as the book Power, Speed, Endurance and the program that inspired it at PowerSpeedEndurance. He is a world-renowned strength and conditioning expert and a co-founder of XPT Life. Mackenzie and his program have been featured in Runners World, Men's Journal, The Economist, Tim Ferris's New York Times bestseller The 4-Hour Body and many other leading publications. Brian works with several CrossFit Games athletes, including champions Rich Froning, Jr. and Annie Thorisdottir. He has also coached and is married to Erin Cafaro-Mackenzie (2X Olympic Gold Medalist in Rowing – W8+) and has guided world and Olympic champions and performance innovators like Laird Hamilton, Taylor Ritzel (2012 Olympic Gold Medalist – W8+), Sara Hendershot (2012 Olympian – W2), Jamie Mitchell, Koa Rothman, Koa and Alex Smith, Nathan Florence and Elliot Sloan.