The swimmers you see are trained athletes. Not just any kind of athlete, but a sport that combines strength, endurance, and core work. Due to their training, they have burned off most of their body fat to get a very lean physique. Thus you are able to see their abdominal muscles. read more
Many, many people go through crash diets and pre-contest nutrition plans in order for their abs to show. However, once they're done with their contest season or diet, they start eating junk food, stop performing cardio, and say goodbye to their six-packs. read more