Fiber type composition and maximum shortening velocity of muscles crossing the human shoulder

Abstract

A study of the fiber type composition of fourteen muscles spanning the human glenohumeral joint was carried out with the purpose of determining the contribution of fiber types to overall muscle cross-sectional area (CSA) and to estimate the maximum shortening velocity (V(max)) of those muscles. Muscle biopsies were procured from 4 male cadavers (mean age 50) within 24 hr of death, snap frozen, mounted, and transversely sectioned (10 microm). Slides were stained for myofibrillar ATPase after alkaline preincubation. Photoimages were taken of defined areas (100 fibers) using the Bioquant system, and fiber type and CSA were measured from these images. Staining for mATPase produced three different fiber types: slow-oxidative (SO), fast-oxidative-glycolytic (FOG), and fast-glycolytic (FG). On average, the muscle fiber type composition ranged from 22 to 40% of FG, from 17 to 51% of FOG, and from 23 to 56% of SO. Twelve out of the 14 muscles had average SO proportions ranging from 35 to 50%. V(max) was calculated from the fiber type contribution relative to CSA and shortening velocity values taken from the literature. The maximum velocities of shortening presented here provide a physiological basis for the development of human shoulder musculoskeletal models suitable for predicting muscle forces for functionally relevant tasks encompassing conditions of muscle shortening and lengthening.

Expression of Myosin Heavy Chain Isoforms in the Human Supraspinatus Muscle: Variations Related to Age and Sex

“…Our results can complement previous findings using different techniques, such as the study of the supraspinatus muscle architecture [Ward et al, 2006], the physiological cross-sectional area of the muscle fibers [Srinivasan et al, 2007], electromyography [Basmajian and de Luca, 1985] and muscle fiber types [Lovering and Russ, 2008], and can help increase our understanding of the functional aspects of the supraspinatus and provide insights into one potential cause of SAIS.…”

“…Both SDS-PAGE and RT-PCR are indicative of the higher expression of the fast MHC-II isoforms compared with the slow MHC-I isoforms in the human supraspinatus muscle, although MHC-I shows the highest expression when the three isoforms are considered separately, followed by MHC-IIa and finally by MHC-IIx. The proportion of type-I fibers observed by ATPase staining [Srinivasan et al, 2007] and immunohistochemistry [Lovering and Russ, 2008], 50 and 54%, respectively, is higher than the 36.72% observed by us for MHC-I expression using RT-PCR. The higher values observed by the former studies could possibly be affected by the presence of hybrid fibers expressing both MHC-I and MHC-IIa [Smerdu et al, 1994].…”

Determination of upper extremity muscle strength profile of Turkish weightlifting national team athletes

“…The angular velocities where this ratio existed were as important as the ER/IR ratio during the assessment of the study results. Therefore, it must be considered that the agonist/antagonist ratio can change depending on the fiber types contained by the muscles when the angular velocities change (29). No comparison was made for the findings obtained at 240º/s in the present study because no study available in the literature was conducted on weightlifters.…”

Effect of velocity on shoulder muscle recruitment patterns during wheelchair propulsion in nondisabled individuals: Pilot study

“…The high proportion of slow fibers in these muscles is associated with their roles in postural maintenance and shoulder joint stabilization. The PD had a particularly high average slow-fiber proportion of 56 percent [36]. During the slow speed test, the larger θ values were recorded in the PD muscle, reflecting the predominantly slow population of MUs within this muscle.…”

“…This may indicate that a greater proportion of fast MUs were recruited to meet the mechanical requirements of the faster motion. Studies of the fiber-type composition show that the deltoid muscles and UT muscles have a high proportion of slow fibers [36]. The high proportion of slow fibers in these muscles is associated with their roles in postural maintenance and shoulder joint stabilization.…”