Study on shoulder muscles by athletic training professor reveals new facts

May 7 2008

Can your shoulder muscles act to protect you from something coming at you without you even thinking about it, regardless of what position your arms are in? A study by Indiana State University athletic training professor Kellie Huxel, published in the January 2008 issue of The Journal of Bone and Joint Surgery, says yes.

Based on previous research performed on cadavers, common wisdom held that when the shoulder joint is in a compromised position, such as with arms up and behind the head, like a baseball pitcher’s, the shoulder muscles are less effective, and therefore would not be able to protect the joint as well.

In Huxel’s study, “Stiffness Regulation and Muscle-Recruitment Strategies of the Shoulder in Response to External Rotation Perturbations,” which looked at 40 healthy, college-aged males and females, she found that the shoulder was just as stable with arms up and behind the head, as it was when the arms seemed to be in a more prepared position directly out at the sides.

“We believe that the body knows how to protect itself, regardless of the position it is placed in.” Huxel said, “It just uses different tissues to get the important information to the brain that triggers muscle contractions to stabilize and protect it.”

When something is coming toward a person, the brain knows how much to turn on the muscles, based on past experience and anticipation, Huxel said. This information from past experience is stored in the brain and accessed when a similar situation occurs.

Huxel used the example of a person versus a leaf.

“You will instinctively turn your muscles on more for another person coming at you than for an errant leaf falling across your path,” she said. “Before our study, we thought that the position of the joint affects how much, or how well, muscles can turn on for these purposes, because of the anatomy of the joint and muscles; but we didn’t find this to be the case.”

What this suggests, Huxel said, is that healthy people are not at increased risk for injury when their arm is in an awkward position, such as back and overhead, like a pitcher’s.

“Your body knows how to adapt and protect itself if it is healthy,” she said.

What this also means for athletic trainers, as well as the everyday person, is that muscles need to be exercised at a variety of joint positions so that when they “kick on” to protect the joint, they can elicit an adequate response, Huxel said.

“In addition to pull-ups and push-ups, which will strengthen the muscles, do exercises that will focus more on stability and the smaller muscles around the shoulder,” Huxel said. “For example, use elastic tubing to target the rotator cuff muscles and shoulder blade muscles; the rhomboids, lower trapezius and serratus anterior.”

Huxel recently received a grant from Indiana State University’s research committee to conduct a related study that would help determine how the natural processes of aging affect shoulder stability.

“We know that older adults are at increased risk for injury due to the aging processes, but we don’t know how aging impacts the muscle’s ability to stabilize,” Huxel said. “This new study may provide us with information to develop prevention and specific rehabilitation plans for this population, which is greatly needed, because people are staying active longer in life and need us to be able to care for them knowledgeably.”

Additional related research on the rotator cuff muscles of adults in two age groups -- those aged 50 to 64, and those 65 and older -- is being conducted by ISU athletic training graduate students Benjamin Fraser and Takayuki Sakurai.

“We are hoping to determine when certain physiological changes start to occur in older adults, which in turn can help us implement shoulder injury-prevention programs at the right time period in an older adult’s life,” said Fraser of Racine, Wisc. “I took on this research project because I liked the idea of working with older adults. It gives me the chance to experience athletic training outside of the playing field.”

Sakurai of Ishioka, Japan, has a particular interest in the neuromuscular control of the shoulder and hopes to work as an athletic trainer for a baseball team.

“We know it takes more time for older adults to recover from injuries,” Sakurai said. “But if we could discover stabilizing strategies, such as the way they activate their muscles, we might be able to prevent those injuries by providing them with better rehabilitation programs.”

ABOUT ISU’S ATHLETIC TRAINING PROGRAM
One of the first four undergraduate athletic training programs in the country (1969); and one of the first two graduate athletic training programs in the country (1972), and the first to admit women, Indiana State University’s athletic training program enjoys a national reputation with a network of alumni throughout the world at professional sports organizations, universities and in health care settings.

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PHOTO: Download a high-resolution photo here: Shoulder muscles study

CUTLINE: Electrodes taped onto the skin collect electrical information from the muscles, letting the researchers know when and how much they are activated. The information is then sent to the computer where it is analyzed. Several muscles around the shoulder are measured to know how the study participant stabilizes his or her shoulder. Pictured is an outline of the scapula; the numbers represent each muscle that will be tested and its location.

CONTACT: Kellie Huxel, assistant professor of athletic training, Indiana State University, 812-237-7694 or khuxel@isugw.indstate.edu

WRITER: Katie Spanuello, media relations assistant director, Indiana State University, 812-237-3790 or kspanuello@isugw.indstate.edu

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Story Highlights

Athletic training professor Kellie Huxel has made new discoveries about shoulder muscles which have been published in The Journal of Bone and Joint Surgery; graduate students are conducting follow-up research.

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