On any given day there are a significant number of MLB players out with oblique strains. These injuries can keep a player on the DL for longer than expected. Here’s a little insight as to what these muscles do and why injury is so prevalent.
First a little background on the “core”
The internal and external obliques are just two of the abdominal muscles that are part of a group often referred to as core muscles. The core is comprised of the more central muscles of the body, those that are part of the lumbo-pelvic-hip complex. Not all core muscles attach directly to the vertebrae, yet they provide stability, enabling safe and efficient movement throughout the body while minimizing injury risk. Some core muscles also serve to support our internal organs. A table of core muscles is provided here.
The abdominals include the transverse abdominus (the innermost layer that you can feel contract when you cough), retctus abdominus (the six-pack in front), and the internal and external obliques (see below). Other core muscles include the quadratus lumborum (a broad muscle in the low back), multifidus (a deep muscle that runs along the spine), muscles of the pelvic floor, the diaphragm, as well as the psoas (a hip flexor), gluteus medius and other muscles of the hip.
When strengthening the core it is ideal to work on controlled functional movements with sustained core stabilization rather than isolating the muscles with exercises such as sit-ups; hence the popularity of planks and a variety of other exercise programs like Pilates. Strengthening that addresses the extremities to the exclusion of the core will not optimize functional strength, and will likely lead to injury from undue stress – whether to the spine or the extremities themselves. Even “isolated” strengthening of the extremities should include a focus on a stable core and avoid compensatory movements in the spine. For instance, if you have to arch your back to do a bicep curl, you are lifting too much weight, doing too many reps, or simply not engaging your core musculature properly.
The obliques are the abdominal muscles that rotate and side-bend the trunk. The fibers of the obliques are oriented in a diagonal pattern, with the internal obliques (the innermost layer) going in one direction and the external obliques (the outer layer) in the other. They attach to the low back, ribs, the pelvis and the midline of the abdominals. For pictures of these muscles, look here.
What do the obliques do and how are they hurt?
Though the internal and external obliques have opposing functions, when working together they assist in forward flexing the trunk. In baseball, these muscles are most likely to be strained due to the powerful and explosive torsion motions required when batting and pitching. In addition, strong lower bodies resulting from focused conditioning generate powerful forces that translate up through the trunk during sports. This as well as restricted hip mobility – not unusual in this population – can also predispose to oblique injury by placing excess demand causing strain.
The Internal Obliques
The diagonal orientation of the internal obliques is key to understanding their function. When they contract (shorten), the internal obliques act to side-bend and rotate the torso toward the same side. In other words, a right-handed batter forcefully contracts his left internal obliques to rotate his trunk to the left as he moves into the swing and follow-through. That is why occasionally, when a switch hitter returns to the line-up after resting and rehabbing an oblique injury, you will see him bat only from the side that does not emphasize the oblique that is injured.
Another important function of the internal obliques is to assist in respiration. They work when we exhale forcefully to draw the diaphragm up, thereby forcing air from the lungs. Normal exhalation, which is a more passive motion, does not involve the obliques.
The External Obliques
The external obliques run on a diagonal that is more or less perpendicular to their more internal counterpart. They assist in side-bending and rotating the trunk toward the opposite side. That means that the right external obliques act with the left internal obliques to swivel the trunk to the left when a batter bats right-handed. They also serve a role in respiration, and that is to assist with inspiration (breathing in) by pulling the chest downward and compressing the abdominal area to allow for expansion of the lungs with air.