Floor Crunch With Back Flattening
Lay on the floor (on your back) with your knees bent in a comfortable position. Activate your lower abdominal muscles and flatten/push your low back into the ground. Work to maintain this contraction throughout the exercise. If holding the contraction is too difficult and is distracting you from the crunch, you can support your legs on a chair/couch/etc. with your knees bent around 90 degrees. This keeps pressure of your back so you can focus on the abs.
Then use your upper abdominals to raise your head and shoulders off the ground. This must be very slow and controlled and once you start, your abdominals should not relax completely until the set is over. Be sure to keep your tongue on the roof of your mouth when your head is off the ground to fully engage your neck muscles. Focus on feeling a tight contraction in your abdominals and breathe out while rising off the ground.
Don’t worry how far you get off the ground, because if you raise up too high, your shoulders and back will be working instead of your abdominals. Perform around 15 reps, but stop if you no longer feel a strong contraction in your abdominals or if you feel tightness in the back of the neck (tightness in the front neck muscles is not a problem).