Last week, impressively fit Beachbody trainers Joel Freeman and Jericho McMatthews led a Core De Force Live class at the CanFitPro fitness expo in Toronto. The mixed martial arts-inspired workout, created by the duo and launched as a home program last November, is a core-centric workout true to what you’d see in an MMA or jiu-jitsu class, minus the contact (no one gets kicked in the face).

“We designed it so a true fighter, who we train with, would look at this and say, ‘That’s legit,’” says Freeman of the movements in the class. “From a physiological standpoint, it’s one of the best ways to train you body.” Beyond that, the growing popularity of the workout can be tied to the current women’s empowerment movement. “This style of workout gets you into great physical shape, but more than anything, it allows you to tap into a deeper place,” explains McMatthews. “When you are throwing kick and punches, there is just something really empowering and strengthening about that.”

Watching her perform these moves, I could see how this is true. It also made me wonder what she was using to keep her amazingly thick waist-length hair out of her face. The answer? Nylon rubber hair ties she buys from a Hong Kong-based company called Uxcell. “My twin sister found these amazing hair-ties on Amazon,” says McMatthews of the elastics. “They’re industrial-strength, they’ve changed my life.” She always has them handy, she says, as does Freeman, who had one on his wrist as a back-up for McMatthews as we spoke. “Otherwise I get whipped in the face [with her hair],” he explains. McMatthews gave me one off her wrist to try, and after wearing it through a vigorous HIIT class, I can confirm they live up to the hype.