When you were young, you probably didn't spend too much time thinking about preparing your body for the future. In your teens and twenties, you're in peak condition and it's the perfect time to start exercising. Cut to 20 years later and, if you didn't start exercising, you probably wish you had since there's something we all start to experience in our 40's—weight gain.
People naturally lose muscle after 40, especially women after menopause. Because muscle burns more calories than fat, this can slow down your metabolism and make it harder to shake those stubborn pounds. Strength-training exercises -- lifting weights or doing body-weight exercises, like push-ups and squats -- at least twice a week can help you keep those muscles.