If you’re not the powerhouse you were in your cheerleading days, here’s why: Women begin losing muscle mass slowly at 30 and, after 50, the decline starts to accelerate. A sedentary lifestyle is also a contributing factor—a double whammy for some. The result is weakness that can lead to injuries down the road and make simple chores like lifting grocery bags a challenge. But don’t despair or resort to a rocking chair. There is a remedy—strength training.