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.

One study with women showed a much bigger muscle growth difference than the others — all of which were only with men — suggesting sex might matter, but we need more studies to know for sure.

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.

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 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.

Men naturally have bigger fast-twitch muscle fibers than women, even if neither exercise, showing a clear biological difference between sexes.