After doing strength training for 12 weeks, older women—whether they started strong or weak—gained about the same amount of strength in their arms and the same amount of muscle, no matter how strong they were at the start.

After 12 weeks of lifting weights, both strong and weak older women gained about the same amount of muscle—starting strength didn’t affect how much muscle they built.

Older women who started out weaker in their legs got stronger in their legs more than the stronger ones after doing leg exercises for 12 weeks, but everyone gained about the same amount of muscle and upper-body strength.

When older women lift weights for 8 weeks, their muscles don’t get much bigger, but they do get stronger and walk faster—so it seems like something other than bigger muscles is helping them move better.

After doing strength training for 8 weeks, older women got stronger and their muscles worked better—but their muscles didn’t get bigger. This suggests their brains and bodies got better at using the muscles they already had, not at making new muscle.

If you're already strong and lift weights, training each muscle group either once or five times a week for eight weeks will give you about the same strength gains on the bench press, squat, and row.