When Pauline ’s physical therapist suggested that she start strength training, he never imagined she’d become a competitive powerlifter. At 76, Ms. Horn turns heads in the gym when she deadlifts 185 pounds five times in a row. “I don’t think what I’m doing is unusual, but everyone else does,” she says.

Nearly three years ago, Ms. Horn was suffering from a torn meniscus and two arthritic knees. She started doing strength exercises at home using body weight and dumbbells, but quickly lost motivation. Her physical therapist introduced her to the Baltimore Kettlebell Club and she got hooked on learning proper weightlifting techniques.

She started with group kettlebell classes and exercises that helped strengthen the stabilizing muscles around her knees. Ms. Horn is one of a handful of women in their 50s, 60s and 70s who train there. Other gym members call them the Golden Girls.

A year-and-a-half ago Ms. Horn started taking strength and conditioning classes with the gym’s owner, Dan Cenidoza, a former winner of Maryland’s Strongest Man competition. Under his guidance, Ms. Horn started powerlifting. Unlike Olympic weightlifting, which involves performing two high-velocity lifts overhead, powerlifting is less technical and focuses on completing three controlled, heavy lifts—a squat, bench press and deadlift. “It’s very empowering to see how you can keep getting stronger,” she says.

Last March, Ms. Horn entered a local powerlifting competition and broke three state records with a deadlift of 170 pounds, a bench press of 77 pounds and an 82-pound squat. In September, she competed in the USA Powerlifting Bench Nationals in Scranton, Pa. “I was the only one in my age group, so I won by default,” she says. “You just have to outlast everybody else and you’re a winner.”