Side crunches are an abdominal exercise that targets the oblique muscles – the largest and outermost of the abdominal muscle group. The oblique muscles lie on the ilium and the fifth through 12th ribs, connecting to the rectus abdominis fascia. While the side of the abdomen is a trouble spot for many people, conditioning of the obliques allows for increased rotation and strengthening of the spine.
Basic side crunches are performed by lying on the floor, back flat on the floor, with knees bent and turned parallel to the floor at hip. The head and torso are raised slightly off the floor and lowered slowly to 1 inch (about 2.54 cm) above resting. After completing the desired number of repetitions – typically 25 to 50 – the exercise can be repeated on the opposite side.
There many variations of the basic side crunch. The first, and perhaps the most popular, is the straight legged variation in which a person lies on his or her side with the inside arm stretched horizontally across the floor. In this variation, the head is turned sideways as opposed to forward as in the basic crunch. Knees remain strait and ankles together.
Side crunches may also be performed with the back flat on the floor and knees aimed at the ceiling. This variation is like a basic crunch, except that instead of simply raising one's torso up, the torso is raised and turned to one knee. Many people find it easier – and more effective – to cross an ankle over the knee opposite the direction the torso is turning. This allows for increased rotation, resulting in further contraction of the oblique muscles. After a set of 25 to 50 repetitions, the knees can be switched and the exercise repeated on the opposite side.
While the primary focus of side crunches is the oblique muscles, the front abdominal muscles are used as well, most acutely in twisting or turning variations. One of the most effective of these is the alternating knee lift variation. To begin, a person lies flat with the lower back pressing into the floor; from there, an opposing knee and elbow are simultaneously raised until contact is made between them, at which point the knee and elbow are switched and the torso twists in the other direction. What is important in this variation is that neither the shoulders nor the feet return to the floor until the set is completed. Because side crunches are more difficult when shoulders and feet are off the floor, sets of this variation typically consist of 15 to 50 reps, as opposed to the minimum 25 for most exercises.