Metabolism Retraining Hint--No Crunches Required 

Top 3 Core Exercises For Flat Abs By Kevin DiDonato MS, CSCS, CES

1. Plank

This exercise looks similar to the push up, but you are resting on your forearms.
You want your elbows in line with your shoulders.
Contract your abs and lower back, pushing your hips into the air. 
Your entire body should be in a straight line.
Hold this position for 10 to 30 seconds.
To make it harder, add CONTROLLED leg lifts to the exercise.  Only lift your legs to hip height.

2. Side Plank (side bridge)
Start with your body resting on your forearm and side of your foot. 
Lift your body off the ground, balancing on your foot and forearm.
Contract your abs and relax your shoulders. 
If you are unable to keep your hips and legs off the ground, then your core needs work.

3. Standing Chops w/medicine ball or cable
The cable or medicine ball is extended over one shoulder.
Start by pulling the cable or medicine ball downward and across your body, keeping your arms extended.
Finish with your arms extended at your opposite hip.

Strengthen Your Core
Your core is the powerhouse for ALL exercise and movements.
The core includes your abdominals and lower back, AND the muscles located in your lumbo-pelvic-hip complex, which may help stabilize your spine during dynamic movements.

Crunches are one of the least effective exercises for developing core strength and endurance.

Incorporating core strengthening exercises may help develop your core, leading to a strong and toned midsection.