Rigor mortis question!?

Question

I was taught that e.g in touching your shoulder with your hand,our biceps allow us to move by one muscle contracting while the opposite muscle relaxes. I was also told that if all our muscles contracted at the same time, it would break our bones. Is it not true that in rigor mortis all the muscles contract-do bones therefore get broken because of this?

Answer 1

The muscles don't contract during rigor, they become stiff and unable to move for a length of time until the lactic acid that has collected in them begins to break down, when they become flaccid again.  

Answer 2

What an interesting Question!

Calcium is necessary for muscles to contract.  Too much calcium = muscle cramps.

Oxygen is necessary to help pump calcium out of muscle cells to prevent cramps.

In a dead person, no oxygen is available, so calcium builds up in the muscle cells, keeping them slightly contracted (stiff).

This is called rigor mortis.  It continues until muscles begin to decompose, releasing the calcium.  This takes about 72 hours.

Since the muscles only contract slightly, not fully, no bones are broken.  The joints do become very stiff, though.