When men and women do strength training, their big, powerful muscle fibers grow about the same amount—neither sex consistently gains more muscle than the other.

When men and women do strength training, men tend to gain a little more muscle size than women—not because they work harder, but because they usually start with more muscle to begin with.

When men and women who are healthy and in their 20s to 40s do strength training, they both gain about the same amount of muscle relative to how much they started with—men might gain a tiny bit more, but it’s so small it doesn’t really matter.

After doing strength training, men might see a tiny bit more muscle growth in their slow-twitch muscles than women, but we’re not super sure because the studies were small and measured muscle samples in different ways.

When men and women do strength training, their fast-twitch muscle fibers grow about the same amount—so sex doesn’t really make a difference in how much these muscles get bigger.

When young men who don't normally exercise do eight weeks of weight training, their fast-twitch muscle fibers get bigger, but their slow-twitch fibers stay the same size and the overall mix of muscle types doesn't change.