According to Huffington Post's columnist and fitness expert, Ben Greenfield, the best exercises to flatten the belly are the squat and the deadlift, To maximize the abdominal workout in a squat, he recommends holding a weight while performing the exercise. The deadlift is similar, but involves picking a weight off the ground while using good form that utilizes your hips and legs rather than your lower back.
Exercise physiologist, Declan Condron, told Shape magazine that the squat works to flatten the belly because it forces the body's core to stabilize the trunk, activating all of the abdominal muscles at once. Condron added that these muscles are all far more engaged during squats than during more conventional sit-ups.
Harvard Medical School also supports the idea that squats are effective in strengthening and conditioning the body's core, including the abdominal muscles. Meanwhile, crunches and sit-ups, both of which were long considered the primary forms of abdominal exercise, are no longer popular in fitness circles owing to their tendency to cause back pain by focusing too narrowly on the abdominal muscles. Today's personal trainers are more likely to suggest a regimen including squats, lunges and planks for those interested in obtaining flat bellies.