What happens when you stretch?

"Just as the total strength of a contracting muscle is a result of the number of fibers contracting, the total length of a stretched muscle is a result of the number of fibers stretched -- the more fibers stretched, the more length developed by the muscle for a given stretch."

This quote summarizes well the limits of the "stretchability" of our muscles. Our bodies are only as capable as the structures within it, so naturally our functions match the number of fibers which are the elements that elongate during the process of stretching a muscle.

"Proprioceptors (also called mechanoreceptors) are the source of all proprioception: the perception of one's own body position and movement."

Alas, a new word. Proprioceptors are also called mechanoreceptors because I believe mechano- refers to the mechanical movement of machines, which our bodies are capable of. Machines aren't necessarily robots or electronic devices. It's actually a simple term in physics that means something that is capable of work. Therefore, our body is a machine, as it can use energy to work!

"When an agonist contracts, in order to cause the desired motion, it usually forces the antagonists to relax."

We learned about the prime mover and the antagonist in a recent lecture, and this goes in further to explain why exactly they are opposites. Not only do they counteract each other in contracting of a muscle, but in stretching as well, they also do opposite actions to stabilize the body while maintaining the action of work and stretching. 

Relate and Review
I'm pretty sure most of us knew that muscles contracted and stretched, because we either learned about it a long time ago, or we just realized it naturally in our daily movements. It's really fascinating to actually find out why and how it works, and it's also really cool to know that it's not exactly a simple task. While picking up a pencil may seem like a difficult task, there's the neurons that deliver the message to move, there's the fibers in our muscles to contract and relax accordingly so we can bend down and wrap our fingers around the object of desire. I can't wait to find out more, because at this point I don't know much, and there's definitely a lot more to the muscular system than contracting and stretching. It's also super fun to be able to know a little bit of physics along the way!