Building a ripped set of abs to show off around the pool or just admire at home requires dedication to exercise and attention to your diet. A number of exercises, including crunches and sit-ups, are effective for strengthening your rectus abdominis muscles. Despite the strength-building benefits of this type of workout, it doesn't burn calories quickly.
A Low Burn
Ab-targeting exercises burn calories at a low rate because they don't cause a drastic increase in your heart rate -- as is the case with an effective fat-burning exercise such as running. Ab workouts are also difficult to sustain over an extended period of time; while you might be able to take a 60-minute run, you couldn't realistically perform crunches for this duration. HealthStatus notes a 160-pound person burns 54 calories in 10 minutes of moderate crunches and 98 calories in 10 minutes of vigorous crunches.
More than Visual Appeal
Strong core muscles aren't always noticeable. If you carry fat over your abdomen but routinely strengthen your core, these muscles will be strong without being visible. Regardless, core strength can help you execute a number of daily movements, including bending and turning. If you have back pain, a strong core can contribute to pain relief.