The obliquus externus, commonly known as the external obliques, are a pair of muscles located on the sides of the abdomen. They are part of the larger group of abdominal muscles that work together to support the trunk and facilitate a wide range of body movements.
Anatomy of the Obliquus Externus
The obliquus externus is the largest and most superficial of the three flat muscles on the side of the abdomen. It originates on the external surfaces of the lower eight ribs, specifically ribs five through twelve. Its fibers travel downwards and forwards, similar to the direction your fingers would point if you placed your hands in your coat pockets.
This muscle has several insertion points, attaching to the front half of the iliac crest, which is the top border of the hip bone. It also connects to the linea alba, a fibrous band of tissue that runs down the midline of the abdomen, and the pubic tubercle of the pelvis. These widespread connections allow it to exert force across both the pelvis and the rib cage.
Functions of the Obliquus Externus
When the muscle on one side contracts, it causes contralateral rotation, meaning it twists the torso to the opposite side. For instance, the right external oblique is engaged when you rotate your upper body to the left, a common action in sports like throwing a baseball or swinging a golf club. The muscle also performs ipsilateral side-bending, which is the act of bending the torso to the same side.
When both the left and right external obliques contract simultaneously, they assist the rectus abdominis muscle in trunk flexion, the motion of bending forward, such as during a sit-up. This bilateral contraction also compresses the abdominal cavity, increasing internal pressure to help stabilize the spine during activities like lifting heavy objects or forceful exhalation.
Common Causes of Obliquus Externus Pain
Pain in the obliquus externus most often results from a muscle strain, which occurs when the muscle fibers are stretched or torn. These injuries are frequently caused by sudden, forceful twisting or bending motions that place an excessive load on the muscle. Activities that involve repetitive and powerful trunk rotations, such as tennis, baseball, and golf, can increase the risk of this type of injury.
Symptoms of an obliquus externus strain include a sharp pain on the side of the abdomen, which can be aggravated by movement. The affected area may be tender to the touch, and in some cases, bruising or swelling might become visible on the skin. This information is for educational purposes, and individuals experiencing persistent or severe abdominal pain should consult a healthcare professional.
Strengthening and Stretching the Obliquus Externus
Maintaining the strength and flexibility of the obliquus externus is important for core stability and preventing injury. A well-rounded routine includes both strengthening and stretching movements to ensure the muscle can handle the demands of daily life and physical activity.
For strengthening, the side plank is an effective exercise. To perform it, lie on your side with your elbow directly beneath your shoulder and your legs stacked, then lift your hips off the floor until your body forms a straight line. Another beneficial exercise is the Russian twist, where you sit on the floor with your knees bent and feet elevated, then twist your torso from side to side. Bicycle crunches also engage the external obliques by bringing an opposite knee and elbow towards each other while lying on your back.
To stretch the muscle, a standing side bend is a simple and effective option. Stand with your feet hip-width apart and reach one arm overhead, bending your torso to the opposite side until you feel a gentle stretch along your flank. The supine spinal twist, performed by lying on your back and gently dropping both knees to one side while keeping your shoulders on the floor, also provides a good stretch for the obliques and lower back.