Although everyone covets a six-pack, Bob says that the core tends to be the most underexercised part of the body. After 30 minutes of cardio, 20 of weights and 10 more of stretching, who has the time? But Bob says the abdominal muscles stabilize the body and protect the back, and they're key to preventing injuries and taking a workout to the next level. Experts estimate that as many as 80 percent of us will experience back problems at some time in our lives, so it's worth making time for planks
and other core exercises.