Answer:

Here is an explanation of how to do crunches for best results:

Lie down flat on your back with your knees bent and your feet on the floor (or on an elevated surface like a bench or ball).

Hold your hands wherever you feel comfortable (on your chest or beside your head - just be sure you don't pull on your head).

• The typical crunch is taught by instructing you to simply roll your upper torso forward, bringing your head towards your knees.
  
• This is fine to start with.
  
• To increase the effectiveness of the crunch movement, try push your chest and head up towards the ceiling pushing your lower back flat onto the floor. You can also think of it as trying to push your belly button into the floor.
  
• Your anatomy will automatically cause you to follow a crunching pattern yet trying to crunch up towards the ceiling will increase the tension on the abs greatly.
  
• Hold at the top of the movement for a second and squeeze hard.
  
• Do not lift up into a sit-up as this works the hip flexors and can strain your back.

For more detailed info on the crunch, check out our Exercise section and Abdominal Crunches.

Bottom line, aerobic exercise isn't your best bet for losing fat and showing off those abs. Interval training is what you need.