Fact 1: Muscle contraction occurs when muscle fibers get shorter.

Fact 2: Muscles can only contract and relax.

Given the two facts above, answer the question "What occurs when muscle fibers get longer?" with the following options: 
- photosynthesis
 - rapid expansion
 - kinetic energy
 - cramps
 - relaxation
 - fertilization
 - movement
 - sweating


 

     relaxation    