In years past, muscle injuries in the abdominal area were known by names such as ribcage strains, oblique strains, side strains, abdominal strains, or intercostal strains; with so many muscles overlapping in the area, it was hard to distinguish one muscle from the other prior to the advent of MRI. Now, we can tell the difference between intercostal strains and oblique strains and can treat each accordingly, but a question remains: Are abdominal injuries occurring at a greater rate, both by number and by position, than they have in the past?
As with most of the body’s core regions, many different layers and muscles overlap. The muscles we are most interested in when discussing abdominal strains are the rectus abdominis, internal oblique, external oblique, transverse abdominis, and intercostal muscles.
The intercostal muscles between the ribs are responsible for elevating and depressing the ribs, an important part of the breathing process. There are internal and external intercostal muscles in between each rib. The external intercostal muscle helps expand the rib cage and aids in inhalation, while the internal intercostal muscle helps shrink the rib cage, which assists exhalation. As a side note, the scalene muscles of Thoracic Outlet Syndrome fame are technically intercostal muscles and help, albeit very little, with breathing.
The rectus abdominis, the muscle behind the so-called “six-pack abs” (which remain a dream for many of us), is responsible for flexing the trunk. It starts at the pubic bone and ends at the cartilage of the middle ribs and xiphoid process of the sternum. Mid-substance strains of the rectus abdominis are uncommon in baseball.
The transverse abdominis is the deepest of the abdominal muscles (i.e., closest to the internal organs) and starts at the iliac crest and cartilage of the bottom ribs before attaching over a very broad area in the mid-line of the stomach running from the sternum all the way down to the pubic bone (see image below).
The internal oblique muscle runs very closely to the transverse abdominis. In addition to compressing the abdomen, the action of the internal oblique rotates the body to the same side, i.e. the right internal oblique helps to rotate the body to the right.
Starting at the 5th through 12th ribs, the external oblique runs perpendicular to the internal oblique before attaching on the iliac crest and mid-line in the area of the internal oblique muscle. Unlike the internal oblique, which twists the body to the same side, the external oblique twists the body to the opposite side.
An image of how the muscles are seen together in different layers:
The easy answer as to why abdominal muscles get injured is that the muscles or their attachments are not strong enough when they contract, but the underlying structures are more complex. The abdominal and core muscles have a tremendous amount of responsibility in stabilizing the core while creating rotational power in baseball. EMG studies (here and here) have shown that same-side internal and opposite-side external oblique muscles have their highest activity during maximum rotation exercises. As an example, when a right-handed pitcher is progressing through his acceleration phase, both the left internal oblique and right external oblique are at their most active. Likewise, when a right-handed batter swings, the left internal and right external oblique muscles are at their most active.
The other muscles must prevent the body from being twisted too far, and they must also have a stabilizing effect that also causes high EMG activity. As a general rule, the stronger the oblique muscles, specifically the external oblique, the greater the velocity.
In a study available online now and soon to be printed in the American Journal of Sports Medicine by Stan Conte, Matthew Thompson MD, Matthew Marks, and Joshua Dines MD looks at abdominal muscle strains over a 20-year period from 1991-2010 at the major league level. Using the official MLB disabled list, they identified over 390 abdominal muscle strains; the vast majority of such injuries were to the oblique or intercostal muscles. There was evidence that abdominal muscle strains have increased from the 1990s to the 2000s, but the number still only represents five percent of all disabled list transactions during this timeframe.
Conte’s group could not find any one particular reason for the increase in abdominal muscle injuries. Despite a greater focus on core strengthening over the last decade, abdominal strain rates have not decreased, but Conte suggests that off-season and early-season training regimens do play a role. There was too much variance in the different strengthening programs and conditioning regimens, however, for Conte to be able to focus on individual or team programs.
Unlike many other injuries, surgical management is exceedingly rare of abdominal strains themselves. Traditional treatment of abdominal strains involves rest, ice, pain relievers, and physical therapy before a gradual increase in activity, including throwing and pitching. Aggressive treatment can involve corticosteroid injections under ultrasound guidance after confirmation of a strain by MRI, a protocol used in a study of pitchers by Kathryn Stevens et al. Conte’s group found that average time off the disabled list was almost nine days longer in pitchers than in positional players (Stevens’ group found that pitchers took an average of five more days).
Conte’s study on abdominal strains argues that the rate of those injuries are on the rise. Although the study could not find any one particular reason for the increased incidence, it suggests that hip biomechanics, strength, and conditioning programs all play a role. We have already started to see more aggressive treatment of oblique strains with injections and the results have been so far been positive. We should not be surprised if aggressive therapy with anti-inflammatory medications or with PRP injections becomes much more common in the future.