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00005768-200805001-0153300005768_2008_40_s192_lovering_composition_5miscellaneous< 17_0_1_0 >Medicine & Science in Sports & Exercise©2008The American College of Sports MedicineVolume 40(5) Supplement 1May 2008p S192Fiber Type Composition of Human Rotator Cuff Muscles: 1356: Board #95 May 28 9:30 AM - 11:00 AM[A-28 Free Communication/Poster - Muscle 1: MAY 28, 2008 7:30 AM - 12:30 PM: ROOM: Hall B]Lovering, Richard M.1; Russ, David W.21University of Maryland School of Medicine, Baltimore, MD. 2Ohio University, Athens, OH.(Sponsor: E.G. McFarland, FACSM)Email: rlovering@som.umaryland.edu(No relationships reported)The rotator cuff is an anatomical term given to 4 deep muscles that help stabilize the shoulder complex. The name derives from their function of rotating the arm, and their location, which forms a "cuff" around the gleno-humural joint in close approximation with the joint capsule. The rotator cuff is commonly injured in athletics and is a major focus of sports medicine. Although the anatomy and architecture of each muscle have been described in great detail, these muscles have never been fiber-typed using immunohistochemistry. Fiber-typing is important in modeling function, developing training, and rehabilitation.PURPOSE: To study the fiber-type composition of the rotator cuff muscles in human subjects.METHODS: We harvested tissue samples for all rotator cuff muscles (supraspinatous, infraspinatous, teres minor, subscapularis) as well as the teres major muscle from cadavers (n = 6, mean age = 65 ± 11.7 yrs). Tissues were frozen in liquid nitrogen and sectioned. 10 μm cryosections were labeled with antibodies against myosin (fast or slow isoforms). We also harvested fresh (unembalmed) tissue from deceased subjects (n = 3, mean age 73 ± 13 yrs) and double-labeled tissue sections for myosin and betaspectrin. Gel electrophoresis followed by silver staining was also used to identify and quantify myosin isoforms in fresh tissue samples.RESULTS: All of the muscles were of mixed fiber-types; an average of 43% of fibers labeled positive for slow myosin. Specifically, slow myosin content was 54% in supraspinatous, 38% in infraspinatous, 47% in teres minor, 37% in subscapularis, and 40% in teres major. Mixed MHC isoform distribution was confirmed by SDS-PAGE, which also indicated that Type IIa and IIx fibers were roughly equally present within a given muscle.CONCLUSIONS: Human rotator cuff muscles have a mixed fiber-type. Because we only examined older subjects, we must limit our interpretation to this population. The supraspinatous had the highest percentage of slow fibers, is the one most commonly involved in rotator cuff pathology, and atrophies disproportionately to other muscles with aging. Although reports in the literature suggest that the internal rotators are more fatigue-resistant than the external rotators, interestingly the primary internal rotator, the subscapularis, had the lowest percentage of slow fibers.Fiber Type Composition of Human Rotator Cuff Muscles: 1356: Board #95 May 28 9:30 AM - 11:00 AMLovering, Richard M.; Russ, David W.A-28 Free Communication/Poster - Muscle 1: MAY 28, 2008 7:30 AM - 12:30 PM: ROOM: Hall B540