Planks: SO hard, but damn will they get you snatched! While doing plank exercises, you are working the transverse abdominis muscle. Training this muscle will flatten your stomach, and slim your waist. Not only will planks help you achieve a smaller waist, but they will also tone your shoulders and back. I challenged myself to do this plank workout for a whole month, and I have seen some insane results! I highly recommend doing this every other day so your core has a day to recover in between.