Re: As a person stretches, do their muscle's sacomeres lengthen?

Hi,
	There is a wonderful web site (http://k-2.stanford.edu/~thu/
MusclePages/sarcomere_switch.html) which briefly details the makeup of the 
sarcomere and what happens when a muscle contracts and lengthens.  To answer 
your question here,  sarcomeres do lengthen when one stretches.
	Of course there is a finite length for the muscle (as anyone who has 
"pulled" a muscle knows).  Few muscles are actually ever completely relaxed, 
thus your muscles always have some tension, some overlap of thick and thin 
filaments. Stretching forces the muscle to relax as much as possible and to 
disengage the myosin heads from the thin filaments.  
	I don't know specifically of studies which have measured sarcomere 
length in humans after regular stretching.  My guess would be that in the 
relaxed state, sarcomere length might increase somewhat over time with 
regular stretching.  This increase in length would not be a gain in absolute 
length of the muscle, but a gain in the ability of the muscle to maintain a 
relaxed state.
	Thanks for the question!