You are presented with the question "What do muscle fibers need to do to enable movement?" and the following answer choices: 
- Bend
 - strength
 - exercise
 - ligt
 - It expands
 - shorten
 - Vibrates
 - stay warm

Now knowing that muscle contraction occurs when muscle fibers get shorter and movement is based on the contraction of muscles, choose the best answer.


 

      shorten   