When women work out during the part of their cycle when estrogen is high, they might build more muscle because estrogen helps protect muscles and speed up recovery.

When women go through menopause and their estrogen levels drop, they tend to lose muscle more quickly and their bodies become less efficient at building new muscle.

In young, active women, having higher natural estrogen levels doesn’t seem to protect against muscle soreness or weakness after intense arm exercises — it hits just as hard as when estrogen is low, like in women taking birth control.

When young guys who don’t work out start lifting weights, their muscles grow more because of changes inside the muscle itself—like more hormone sensors and activation signals—rather than because of hormones floating in their blood.

Older women who lift weights—even just one arm or leg at a time—gain muscle and fight off the natural muscle loss that comes with aging.