Sit ups, planks and plank variations, reverse crunches and cross body crunches are powerful moves to strengthen the abdominal muscles. Additional exercises for the stomach include Pilates-inspired moves, as stated by WebMD. Keeping the abs tight as the exercise movement is completed helps make the exercise more effective.
Plank and plank variations use the principle of anti-extension to force the abdominal muscles to combat gravity when the move is performed, as reported by Ace Fitness. Once the plank becomes too easy, the single leg plank, jump plank and spider plank can help make the move more difficult. Altering the position of the hands is another way to adjust the move's difficulty level.
Pilates strengthens the core muscles and encourages participants to be aware of their bodily motions. Popular Pilates moves include the Pilates hundred, the roll-up, the shoulder bridge and the wall chair.