Abdominal exercises are useful for building the abdominal muscles. This is useful for improving performance with certain sports, back pain, and for withstanding abdominal impacts (e.g., taking punches). According to a 2011 study, abdominal muscle exercises are known to increase the strength and endurance of the abdominal muscles.
It has been highly disputed whether or not abdominal exercises have any reducing effect on abdominal fat. The 2011 study found that abdominal exercise does not reduce abdominal fat; to achieve that, a deficit in energy expenditure and caloric intake must be created—abdominal exercises alone are not enough to reduce abdominal fat and the girth of the abdomen. Early results from a 2006 study found that walking exercise (not abdominal exercise specifically) reduced the size of subcutaneous abdominal fat cells; cell size predicts type 2 diabetes according to a lead author. Moderate exercise reduced cell size by about 18% in 45 obese women over a 20-week period; diet alone did not appear to affect cell size