INTRODUCTION

Strong and well defined abdominal muscles are desired by nearly everyone from the college-aged through the middle-aged. These muscles, which include the rectus abdominis and the internal and external obliques, not only play a role in enhancing a person's appearance, but are also of prime importance in preventing postural problems and lower back strain. Two basic exercises commonly used to strengthen the abdominals are the standard sit-up and the crunch. The sit-up is performed while in the supine position with the knees bent and the feet flat on the floor fifteen to twenty centimeters away form the buttocks. The arms are crossed over the chest so that the tips of the fingers touch the shoulders. The person begins by raising their chest to their knees and ends by returning to the original position. The crunch is performed with the limbs in the same starting position as they were in the sit-up. In the crunch, however, only the shoulders and upper back are lifted off the floor, not the whole torso. Is one exercise safer, or less likely to strain the back, than the other? Which exercise more effectively works the abdominal muscles?

The purpose of our investigation is to compare the biomechanics of the standard sit-up and the crunch to determine if one exercise is safer and/or more effective in strengthening the abdominals than the other. Our group's interest in this topic stems from our summer volunteer experience in physical therapy rehabilitation clinics. It was in this environment that we first recognized the role abdominal muscles play in preventing back problems.