Abs are one of the most powerful muscle groups in the body. Strong abs help with posture, the transfer of muscle power from the upper body to the lower body (and back again) and help prevent lower back pain by better supporting the spine. They're also hard to train. The best way to make them stronger is to challenge them and the best way to do that is to take the 30-day ab challenge. 

What it works: Frontal abs, lateral abs, core.  

Tip: For fastest results make sure you pull in your lower abdomen while performing ab-strengthening routines. This flattens the muscles and helps align them better, increasing the pull being exerted and helping to strengthen the abdominal muscle wall, faster.