Basic scienceThe effect of age on rat rotator cuff muscle architecture
Section snippets
Methods
We performed a cross-sectional study of muscle architectural dimensions across the rat lifespan. Thirty healthy Sprague-Dawley rats were euthanized under a protocol approved by the Institutional Animal Care and Use Committee of the University of California, San Diego. The animals were weighed and divided into 6 approximate age groups based on total body mass: approximately 3 weeks (51-70 g, n = 4), approximately 1 month (100-108 g, n = 4), approximately 2 months (229-263 g, n = 7),
Results
Muscle mass increased linearly with body mass in both the supraspinatus and infraspinatus muscles (Figure 2, Figure 3, A). However, normalized fiber bundle length increased nonlinearly (logarithmically) with total body mass (Figure 2, Figure 3, B). There was a weak relationship in the supraspinatus and no relationship in the infraspinatus between total body mass and sarcomere length, which remained constant at approximately 2.4 μm (Figure 2, Figure 3, C) in both muscles. The development of PCSA
Discussion
Our results suggest that the architecture of the rat rotator cuff, in general, develops proportionally with total body mass. In particular, the mass of the muscle dominates the PCSA, and therefore, we would expect that force-generating capacity increases linearly with body mass. Perhaps most interestingly, normalized muscle fiber bundle length increased nonlinearly with total body mass, allowing sarcomere length to be conserved. When these relationships were further explored, we observed that
Conclusion
The development of muscle architectural features in the rat rotator cuff muscles follows linear and nonlinear growth trajectories. By use of these data in the body mass range of 400 to 600 g, as frequently seen in experimental models of rotator cuff tendon injury, a 30% increase in supraspinatus and infraspinatus muscle mass was observed. Similarly, a 7% increase in fiber length, a 27% increase in PCSA, and nearly constant sarcomere lengths were observed. These data indicate that investigators
Disclaimer
The sources of funding for this study were as follows: NIH R01 AR057836, and NIH R24 HD050837.
The authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.
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