What principles related to muscle tissue, structure and function, as noted in the Kossmann/Huxley article, are still relevant today?

This week’s Question is on the topic of muscle tissue, specifically about the relative differences between skeletal and cardiac muscle. I have included an article from the American Heart Association for your review. you can access the article directly at: http://circ.ahajournals.org/content/24/2/328.full.pdf.
This AHA journal article, The Contractile Structure of Cardiac and Skeletal Muscle, by Charles E. Kossmann and H.E. Huxley, was written and published in 1961, and uses some early electron microscope images as “new” evidence, as described by the author, to display the “fine structure of striated muscle”. There is also some interesting discussion of the differences between skeletal and cardiac muscle.
In reading this article, reference back to your textbook, pages 336-347, which describe the same basic principles of muscle structure, functionality and movement, with so much more information and detailed electron microscope photomicrographs to support your study of the muscle system and structure. How fortunate we are that scientists like Drs. Kossmann and Huxley, and others over the last 60 years (60 years since this article was published), had the curiosity and love of science and medicine to pursue the answers to how the body functions.
What principles related to muscle tissue, structure and function, as noted in the Kossmann/Huxley article, are still relevant today?
Is there any theory or questions that the authors had in 1961 that have been resolved or determined?
What is your reaction in general to the article?
Feel free to add other researched articles that support the discussion and include the source reference.