Defined, toned abs — commonly called a six-pack — are an often sought-after goal in the gym. But not all toned abs look the same. Some people sport a four-pack, while others may have an eight-pack.

Add Yahoo as a preferred source to see more of our stories on Google. Experts on why it's so hard to get six-pack abs, particularly for women, and why it's not the only sign of a strong core. (Photo: ...