Women and Muscle Building: What the Research Actually Shows

Women do not need a separate category of “toning” training, and men do not own the muscle-building playbook. Resistance training can increase muscle size and strength in both sexes. The useful question is how the evidence describes average differences without turning them into limits on an individual.

What the 2025 meta-analysis found

Refalo and colleagues analysed 29 studies comparing healthy adult males and females who completed the same resistance-training intervention. Absolute muscle-size increases slightly favoured males, while relative changes from baseline were similar. The analysis also found that upper-body absolute hypertrophy favoured males, whereas lower-body absolute hypertrophy and Type II fibre hypertrophy were not clearly different in the same way. The authors caution that more work is needed in highly trained participants. Read the open-access paper.

“Similar relative growth” does not mean identical bodies, starting points, absolute muscle gain, strength, or response to every exercise. It means that the current pooled training evidence does not justify telling women that they have a fundamentally lower hypertrophy potential.

What should not change by sex alone

For most healthy adults, the same programming principles apply:

• choose exercises that train the target muscles and fit the joints;
• use a load and repetition range that permit challenging, controlled work;
• progress load, repetitions, sets, or execution when performance and recovery support it;
• eat enough energy and protein for the goal;
• adjust for schedule, pain, pregnancy, menopause, medical conditions, and sport demands.

“Women should lift only light weights” is not an evidence-based muscle-building rule. Heavy work can be useful, but the right load is the one that matches the exercise, skill, goal, and current capacity—not a gender stereotype.

Strength is not the same as muscle size

Strength outcomes include technique, leverage, body size, neural learning, and the specific test. A larger relative strength gain in one group does not prove a larger hypertrophy response. Compare progress with the person’s own baseline and use the outcome that matters.

Menstrual cycle and individual variation

Menstrual-cycle symptoms, energy availability, sleep, contraception, pregnancy, postpartum changes, and menopause can affect comfort and performance. The evidence does not support a universal cycle-based programme for every woman. Use symptoms and performance to adjust load or volume, and get clinical advice for unusual bleeding, severe pain, or persistent fatigue.

Individual differences within each sex are large. Training history, exercise selection, adherence, nutrition, health, and measurement noise often matter more to a person’s next decision than a group average.

A useful way to apply the evidence

Start with a repeatable programme rather than sex-specific marketing. Track exercises, repetitions, load, effort, recovery, and the muscle or strength outcome you care about. If the programme is progressing, keep it. If it is not, investigate training, food, sleep, pain, and life constraints before assuming biology has set a fixed ceiling.

Bottom line

Women and men both respond to progressive resistance training. Current evidence suggests similar relative muscle-size changes on average, with some differences in absolute size and selected outcomes. That is a reason to individualise training—not to prescribe lighter weights, special “toning” ranges, or a fixed expectation for any one person.

Related reading

• Menstrual Cycle and Training: What to Individualise
• Training Fundamentals for Muscle Growth
• Protein and Muscle Growth: A Practical Evidence Guide

Applying this article

Use the same evidence-based training principles, then individualise exercise, effort, recovery, and nutrition. Track your own trend and seek qualified advice for pregnancy, postpartum training, menopause, pain, or medical conditions.

Limits of the evidence

The 2025 meta-analysis included healthy adults aged 18–45 and relatively few highly trained participants. Sex, gender, age, health, hormones, training status, and measurement method are not interchangeable variables, and group averages do not predict an individual response.

Sources

• Sex differences in absolute and relative muscle-size changes after resistance training. 2025 systematic review with Bayesian meta-analysis; open full text is linked above.
• Sex differences in resistance training. Earlier systematic review and meta-analysis of strength and hypertrophy outcomes.
• ACSM resistance-training prescription overview. General resistance-training evidence for healthy adults.