All muscle tissues are specialized for contraction, possessing the ability to shorten and therefore create a contractile force. Substantial metabolism is necessary to produce energy for these contractions and a useful by-product of chemical reactions is heat. Therefore, muscles contribute to thermoregulation, the maintenance of body temperature. All muscles are excitable, able to respond to stimuli, an important capability also common to nervous tissues.
Muscles are extensible in that they can be stretched and still maintain contractile ability.
As we will see, some muscles are better at this than others. Finally, muscle cells are associated with elastic connective tissues. These connective tissue elements enable muscles to contract or stretch and then return to their original length, an attribute called elasticity. Muscle types vary in their appearance histologically but one common attribute applies to all varieties, the cells of muscles are long and narrow. For this reason, the term fiber is common descriptive term for muscle cells.