Amid a raucous soundscape of pulsing house music, Vallacher pushes her class hard on the landmine, a long metal pole anchored to the floor that has weights attached to its free end. Over and over, class members lift the pole up and down in a maneuver called “the spear throw.” The high-intensity exercise was part of a six-week training cycle last summer designed to simulate how Vikings in 9th-century Scandinavia may have stayed pumped for pillaging. Vikings? “I’m a big history nerd,” says Vallacher, who has also built strength-and-conditioning workout routines around Olympic swimmer cross–training and summer bodies as a fun way to maximize the physical benefits of periodic training cycles.

The 5-foot-1 powerhouse wasn’t always in great shape. As a young ballerina, Vallacher learned to ignore pain. At Dartmouth she could barely sit due to a tailbone injury. She avoided the gym. “The only sport I played in college was pong,” she jokes. A few years after college, she turned to a personal trainer for rehabilitation. “He took away my pain and gave me my legs back. It blew my mind.”

Today Vallacher and her wife co-own the Phoenix Effect, a fitness studio in West Hollywood, California. In addition to one-on-one training and group coaching, Vallacher runs nutrition challenges and designs workout routines. “I try to help people alleviate their pain and get their bodies back,” she says. “Maybe I can help them see their own beauty, too.”