Re: How does sliding filament muscle contraction really work?

Good question.  The number of sarcomeres is not infinite, so ultimately 
there is a muscle border, where the muscle meets the connective tissue 
tethering it to the bone.  Essentially, the distance between each Z-disc in 
each sarcomere decreases with the tensile force ultimately transferred to 
the very ends of the muscle and tendons and bones.  These move closer 
together - when you move your extended arm toward your head, the distance 
between the muscle "anchoring points" decreases and the bones to which the 
muscles are attached get closer to one another.  So the cumulative force of 
sarcomere force is transferred at the muscle tissue ends to the tendons and 
the non-deformable substratum, the bones, which are pulled closer together.

Imagine a spring - when you pull it out with your hands, each spiral turn 
gets farther apart, and tension is stored in the stretched out thing 
equally.  The effect is that it pulls your hands.  It is pulling from both 
directions, and on a local level, each spiral is pulling on each other.  
The spring is finite and generates force on the ends.

Hop