That depends on what you mean by "tone." That term doesn't have a lot of meaning in the fitness world. :)
Are you talking about building core strength? If you are, exercises like planks will build your core. Yu can't really work individual muscle groups in isolation; they're all connected!
If you're trying to reduce fat in that area, it won't work. Our muscles take their energy from the bloodstream, not the surrounding fat stores.
Writer, mother, wife, and breadwinner. I love to run, but running doesn't love me, so I'm switching to my low-impact bike.
I'm not pregnant, just fat: My blog. fatnotpregnant.blogspot.com/
| current weight: 190.6