Re: Why does if feel good to stretch our muscles after rising in the morning?

Hello Jan!  Thank you for your question.

You asked:  "Why does it feel good to stretch our muscles after rising in 
the morning?  Is it because it gets our blood circulating better?"

We are able to move our body parts because of muscle 
contraction/relaxation.  When the actin and myosin components of sarcomeres 
in a muscle fiber slide across each other, the sarcomere shortens --- 
generating force.  A muscle contracting is simply a whole bunch of 
sarcomeres shortening.  Sarcomeres operate on an "all or nothing" manner.  
They're either shortened or they're not.  So then how do we get gradations 
of muscle force?  By the number of muscle fibers involved.  The stronger 
the action required, the more muscle fibers get involved.

OK, so what does the above have to do with your question?  When we are 
sleeping, our body is sprawled in some sort of position.  Let's say that 
one of my arms is curled up under my pillow.  Regardless of the orientation 
of my arm, for it to have moved into that position required muscles 
cooperating in pairs --- so for my arm, my bicep is contracted while my 
tricep is relaxed.  Sure, I may be "relaxed" because I am asleep, and I may 
not consciously be holding my arm in that position, but the muscle fibers 
in the bicep are shortened and contracted (remember, this is an all or 
nothing phenomenon at the molecular level).  After awakening, stretching 
feels good because you are basically relieving those agonist/antagonist 
muscle pairs of their duties.  Straightening out my arm will cause my 
tricep to flex, taking up the job of contracting, while my bicep gets to 
relax.  Many benefits come from stretching the muscles, the most immediate 
being the relaxation of muscles that have been constricted.  The movement 
of muscles (and limbs in general) promotes blood flow and aids in 
circulation (as you theorized correctly), including the removal of waste 
products that may have accumulated in the muscles (such as lactic acid).  
Stretching increases tissue temperature, and also stimulates the synovial 
fluid in the joints, keeping them well oiled.

Hope this helped!  Feel free to email me at monreal.1@osu.edu if you have 
further questions.

Sincerely, 
G. Monreal

For more information on muscles and stretching, please consult the 
following excellent websites: http://galway.informatik.uni-kl.de/staff/weidmann/pages/stretch/stretching_
2.html http://www.curtin.edu.au/curtin/dept/phys…_old/edres/exphys/ep552_97/stiffn
ess.html http://www.walking.about.com/recreation/walking/cs/stretching/index.htm