If you've done enough aerobic exercise to reduce your belly fat, a 300-crunch workout can result in toned, visible abs. Even if you're carrying a few extra pounds around your midsection, abdominal strength can lead to reduced back pain and improved posture. Although crunches can play a role in your overall fitness, they don't burn calories as quickly as aerobic exercises.
A Low Calorie Burn
Performing 300 crunches per day isn't an easy workout, even if you break the exercise into multiple reps. Additionally, the American Council on Exercise recommends that for abdominal exercises, a maximum of 75 reps is more than enough. If you're fit enough to perform 300 crunches, the calorie burn depends on how quickly you execute each rep. If you perform the exercise at a moderate rate, such as 20 per minute, you'll need 15 minutes to reach 300 reps. If you use a vigorous rate, such as 50 per minute, you'll need six minutes to reach your goal. HealthStatus notes that a 165-pound person burns 84 calories in 15 minutes of moderate crunches and 60 calories in 6 minutes of vigorous crunches.