Optimal Range of Motion: Part 2

Anatomy
We'll continue in this part by going over some basic muscle physiology and anatomy. Our muscles are complex and fairly simple at the same time, to demonstrate this we'll work from the outside in. The outside of our muscles are covered by a layer of connective tissue called the Epimysium, this layer covers the belly of the muscle and helps make up our tendons. Under the epimysium, there is another layer of connective tissue called the Perimysium, this layer surrounds bundles of muscle fibers.  Surrounding the individual muscles fibers is another layer called the Endomysium. All of these layers of connective tissue help with generating muscle force.

Within the individual muscle fibers are what are called Myofibrils. The myofibrils are bundles of proteins and this is where the magic happens. There are two main proteins within in the myofibrils, myosin and actin. These proteins are what cause muscle contraction. The myosin and actin are organized in a way that 6 actin surround 1 myosin. With this configuration the actin and myosin can produce force by the sliding filament mechanism. (Don't worry we won't go into all the details)

Physiology
The jist of the sliding filament mechanism is that myosin and actin form a "ratchet".  The myosin attaches to the actin and pulls towards itself, grabs another portion of the actin and pulls once again. Check out the illustration below. The blue lines represent the actin, while the red represent the myosin.

You're probably wondering what everything else in the illustration is and we're getting to that.......right now.

As you may already know muscles are extensible and can be stretched, when they are stretched the actin and myosin are moved apart. When this occurs the myosin can't make as many connection with the actin and less force is produced. On the opposite end of the spectrum, muscles can contract and shortened in length. This is a good thing but only to a point. As one actin fiber is pulled closer to the center of the myosin, the other actin fiber is being pulled to the center of the myosin. (As seen on the left of the illustration) When this happens the actin can get in the way of each other making it difficult for the myosin to make new connections, thus producing less force.

Application
Overall when fewer connections between the myosin and actin are made, the less force is produced and the less weight can be moved.
When training in the weight room our time and energy is precious and we want to utilize them the best we can.  By limiting full range of motion (i.e no "squeezing" at the end of movement) during targeting exercises we can lift a greater amount of weight.
In climbing and other athletic activities the body is required to move throughout entire ranges of motion. So why train the way explained above?  Just like our example of "weak links" in part 1, we can only train as hard as our weakest link. Physiologically speaking really long and really short muscle lengths are our weakest links and prevent us from training to our highest potential.