The abdominal muscles are essential for maintaining good posture and core stability, however many exercisers are unclear on the correct way to exercise them. Traditional exercises for the abdominals include crunches and sit-ups also known as trunk curls and curl-ups. The following are ten things to avoid when performing exercise for the abs.1. Do not use a machine or contraption of any kind to exercise the abs, body weight and medicine balls are more than sufficient. No contraption or machine.