Muscle Growth in Men and Women: What Actually Differs
Men and women can both gain substantial muscle and strength through resistance training. Average differences in starting muscle size and hormones do not mean women need endurance-only workouts or cannot respond well to heavy lifting. The most useful distinction is absolute muscle gained versus growth relative to starting size.
Muscle Fiber Composition
Muscles contain a mix of slower and faster fibers. Average differences between groups cannot identify an individual’s fiber mix or prescribe their workout.
Type II fibers: These are important for forceful, fast contractions and can grow with resistance training. Their presence is not a reason to reserve heavy lifting for men.
Type I fibers: These are relatively fatigue-resistant and also adapt to resistance training. They are not “endurance-only” tissue, and a presumed higher proportion does not mean women should avoid challenging loads.
A 2025 meta-analysis of 29 studies in healthy adults aged 18–45 found slightly greater absolute increases in muscle size in males, while proportional increases were similar between sexes. People starting with more muscle can gain more in absolute terms without growing faster as a percentage of their starting size.
Hormonal Influences
Sex hormones contribute to muscle biology, but hormone differences do not replace observation of an individual’s training response.
Testosterone: Typical circulating levels differ substantially between men and women and contribute to differences in muscle mass. That does not let you predict an individual’s rate of training progress from sex alone. Short-lived exercise-related hormone changes are also different from long-term hormone status.
Estrogen: It has roles in muscle and bone biology, but it does not guarantee fast recovery after every workout. Training history, the exercise, load, sleep and nutrition also matter. Symptoms or life-stage changes that affect training deserve individual attention rather than a one-size-fits-all sex-based rule.
Upper- and Lower-Body Training
Train both upper and lower body according to your goals. The evidence does not support the claim that women inherently build legs more easily because of type I fibers.
Nor should women assume poor potential for upper-body progress. A 2020 meta-analysis found similar hypertrophy and lower-body strength responses, with greater relative upper-body strength improvement in females. The authors noted that the reasons were uncertain; it is not an individual prediction.
How to Use This in Your Training
Start with exercises and loads you can control, then progress from your own log. For example, if a row target is 3 sets of 8–12, keep the load until all three sets reach the upper end at similar effort, then add a small increment. Use the same decision process regardless of sex, adjusting volume and rest to your actual performance and recovery.
