Compare: She's doing exercises to build up the strength in her legs. She's doing exercises to build up strength. She's doing exercises to build up her strength.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.
AnonymousI was impressed by his strength.When one of these possessives is used (his, my, her, their, ...), it takes the place of an article, so this example is fine. We don't use an article when one of these words is used.