For decades, women have been told they need special workout rules. Don’t lift too heavy. Train around your hormones. Change your workouts throughout the month.
The advice seemed logical. Men have substantially higher testosterone levels, a hormone that plays a major role in muscle growth. “Testosterone increases muscle mass in boys, and so you get an adult 20-year-old man and an adult 20-year-old woman, and there’s going to be differences in baseline muscle size and strength,” says Lauren Colenso-Semple, a researcher and science communicator specializing in female physiology and exercise.
But a growing body of research suggests those differences may matter less than many people assume once training begins. A 2025 meta-analysis published in PeerJ found that women have a similar capacity for muscle growth, known as hypertrophy, as men. While men typically start with more muscle mass, women make comparable relative gains in muscle mass through resistance training.
Once people start exercising, the sex differences disappear quite quickly: “When you think about lifting weights and the magnitude of muscle size and strength that you can gain in response to training, the trajectory is very, very similar in men and women,” says Colenso-Semple.
Although hormones can influence how exercise feels from day to day, there is little evidence that most women need entirely different training programs to build muscle, strength, or fitness. That matters because resistance training remains one of the most powerful tools for improving cardiovascular health, preserving bone density, and supporting healthy aging. But only 27 percent of adult women in the U.S. met the federal guidelines for muscle-strengthening activities in 2020.