If the production of heat occurs when many muscles contract a little bit all at once, then what occurs when many muscles contract a little bit all at once?

Answer choices:
- the production of cells
 - preventing heat transfer
 - To keep their body heat.
 - the production of heat
 - Generating heat
 - recovery time from fatigue
 - the production of cold
 - the production of skin

 

    the production of heat      