Which part of the tendon structure is around 20-100 micrometers?

The subfascicle is indeed the correct answer because it represents an important organizational level of the tendon structure. Subfascicles are formed by aggregations of collagen fibers and generally measure between 20 to 100 micrometers in diameter. This size indicates that subfascicles are larger than individual collagen fibrils, but smaller than fascicles, which comprise multiple subfascicles.

Understanding the organization of tendon structure helps in grasping how mechanical properties are achieved in tendons. Collagen fibrils are much smaller, generally on the order of nanometers, while fascicles are larger bundles that can encompass many subfascicles. The hierarchical structure of tendons, from fibrils to subfascicles to fascicles, allows for the efficient distribution of forces and contributes to the overall strength and functionality of the tendon.