Final answer:
The three reasons for differences in tenderness among muscles are sarcomere length effect, myoglobin effect, and bulk density/lubrication effect.
Step-by-step explanation:
The three reasons for differences in tenderness among muscles are:
1. Sarcomere length effect: The length of the sarcomere, which is the basic functional unit of muscle tissue, has a direct influence on the force generated when the sarcomere shortens. This is called the length-tension relationship.
2. Myoglobin effect: Myoglobin is a protein found in muscle cells that stores and transports oxygen. Muscles with higher myoglobin content tend to be more tender because they have a greater capacity to deliver oxygen.
3. Bulk density/lubrication effect: The bulk density or lubrication of muscle fibers can affect tenderness. Muscles with a higher density or more lubrication between fibers tend to be more tender.